08-MILITARY MEDICAL EVACUATION

Chapter 27MILITARY MEDICAL EVACUATIONCOLIN A.B.McLAREN,QHP,MB,CHB,FC ANAES*;LOUIS M.GUZZI,M.D.t;AND RONALD F.BELLAMY,M.D.INTRODUCTIONHISTORYLOGISTICAL AND OPERATIONAL ASPECTSUnit and Division LevelsCorps and Communications Zones:Zone of the InteriorDomestic Aeromedical Evacuation SystemMEDICAL IMPLICATIONS OF BIOPHYSICAL EFFECTS OF AEROMEDICAL EVACUATIONBarometric PressureOxygenationGravitational and Accelerative ForcesThermal StressNoise and VibrationFatigue and Sleep LagMEDICAL DETERMINANTS OF SAFE EVACUATIONIn-Flight Medical Problems of Long-Range Aeromedical Evacuation Patient Conditions Leading to Medical InstabilityPreparation for EvacuationSUMMARY*Formerly,Air Commodore,ConswltantAdoiser Anaesthetics,The Royal AirForce(ret);Central Medical Establishment,Keloin House CleoelandStret,London,WIP 5FB,England;Currently,Consultant Änaesthetist,12 Broadacres,Broad Toon,Woton Bassett,Wiltshire, SN47RP,England+Major,Medical Corps,U.S.Army;Chief,Combat TraumaResearch,Walter Reed ArmyInstitute ofResearch,Washington,D.C.20307-5100#Colonel,Medical Corps,U.s.Army;Managing Editor and Offcerin Charge,Textbook of Military Medicine,Borden Institute,Walter ReedArmy Medical Center,Washington,D.C.20307-5001Anesthesia and Perioperative Care of the Combat CasualtyINTRODUCTIONUnless an army is prepared to deploy its major medical assets,including its hospitals,into the middle of a battlefield,it must be capable of carry- ing out that&quot;undeniable but unavoidable evil of evacuation of the sickand wounded,&quot;l in the words of Nikolai I.Pirogov,one of the founders of 19th century military surgery.Pirogov's useof the word “evil”may seem extreme,but harmful effects can arise duringevacuation,especially when itis viewed simply as transportation.That military medical evacuation is more than transportation is clear from its official definition. According to U.S.Army Field Manual(FM)8-10-6,Medical Evacuationina TheaterofOperations,militarymedical evacuation includes₂(P4-D:·collecting the wounded,·performing triage,·providing an evacuation mode ortranspor- tation,·providing medical care en route,and·anticipating complications andbeingready to performemergencymedicalinterventions.Evacuation is not an end in itself but,at a mini- mum,is a tool that makes possible more effective treatment.At the same time,by allowing the de- ployment of the most logistically demanding,im- mobile,and vulnerable medical assets far to the rear,evacuation simplifies the commander's com- bat service support mission.Ideally,treatment is ongoing during evacuation.Implicitin the officialdefinition of medicalevacu-ationis the fact that the act ofevacuating casualties covers a wide spectrum ofcontingencies that range from·manual evacuation(by two-man carry)ofthe casualty to a sheltered site 100 m dis-tant,to·ground ambulance evacuation to a battal- ion aid station several kilometers distant,to·helicopterevacuation to amobile army sur- gical hospital(MASH)30 km distant,to·intratheater(ie,tactical)aeromedicalevacu-ation by fixed-wing aircraft to a communi- cation zone hospital 300km distant,to·intertheater(ie,strategic)aeromedicalevacuation by long-range transport to a hospital in the zone of the interior 10,000 km distant.Not surprisingly,the indications for evacuation, the medical diagnoses of the evacuees,and the differing technical characteristics of the means of evacuationinteract to produce a variety of potential medicaltreatment problems.However,certain ba- sic medical truths predicated on human anatomy and physiology remain constant and cannot be ig- nored without dire consequences for the casualty. The potential medical“evil”of evacuation,espe- cially that which may arise from the physiological threat of aeromedical evacuation,is the primary subject of this chapter.HISTORYMost ancient armies had medical staffs to look after their sick and wounded,but it would seem that their chief responsibility was to attend to the well-being of officers and princes.3 The problems of removing the sick and wounded from the battle- field were probably not viewed as oneof the func- tions of the medical staff but rather as a logistical problem that needed to be solved:the dead and dying on the battlefield interfered with thefighting. Such considerations no doubt motivated the first well-documented instance of evacuation,namely, when Scipio temporarily broke off his ultimately successfulattackon Hannibal in the climacticbattle of the Second Punic War at Zama in 202 Bc:The space between the two corps which still re- mained on the field was by now covered with blood,corpses,and wounded men,and the physi- cal obstacle created by the enemy's rout presented a difficult problem to the Roman general.Every- thing combined to make it hard for himtoadvance withoutlosingformation:the groundslippery with gore,the corpses lying in blood-drenched heaps, and the spaces between encumbered with arms that hadbeen thrown away at random.However, Scipio first arranged for his wounded to be carried to the rear...4(p479It is unclear when the rationale for evacuationwas first looked on as medical rather than as thelogistical process of“clearing thebattlefield.”Cer- tainly by the Napoleonic era,some military sur- geons recognized that early evacuation from the battlefield even before the fighting had ended was a necessary prerequisite for effective treatment. Foremostamong them wasDominique-Jean Larrey, who was surgeon to Napoleon's Imperial Guard.Larrey'srecognition of the need toimprove evacu- ation preceded any of Napoleon's battles,and he presented his conclusions regarding evacuationata conference held on 17November 1789.This confer- ence was convened in Paris by the National Con- vention of the Revolution to study Larrey's report describing the medical treatment of French troops fighting in the battles of Limbourg and Speyer.5 At this time,the treatment,or lack of it,depended on the result of the battle:success meant that the casu- alty would receive some sort of treatment,albeit48 hours after wounding,whereas defeat meant no care and almost certain death.Larrey pursued his ideas despite his initial lack of success.He developed the use of horse-drawn vehiclesto evacuate the sick and wounded from the battlefield via the ambulance volante (ie,flying am- bulance),which was first used in 1797 on thebattle- field of Konigstein,in the Taunus mountains of the Rhineland Palatinate.Although Larrey's flying ambulances were available in only a tiny part of Napoleon's army,their ability to providerapid and humane evacuation was widely recognized.James McGrigor,Wellington's outstanding chief medical officer in the Peninsular campaign,in attempting to justify the acquisitionof similar vehicles,wrote the following classic description of evacuation gone wrongThe suffering of the sick and wounded was very great...They sufferedso much by the transport [ie, slow,cumsy ox-carts—RFB],the weather,and the privation...that...many of the wounded and those ill of dysentery arrived in so bad a state as only to survive a few days....6(p121)Other modes of transportation were adopted for the evacuation of casualties during the 19th cen- tury.Florence Nightingale was instrumental in organizing hospital ships to evacuate the sick and wounded during the Crimean War.(The first re- ports of the use of ships for the transfer of the wounded had occurred during the Eighth Crusade, whengalleys were used tomove them to Damietta.3) At the same time,the rapid growth of railways as the principal mode of transportation offered anMilitary Medical Evacuationalternative.Given the appallingstate of theroadsin any battle area and the congestion of vehicles trav- eling to the battle area (causing delays with the ambulances traveling in the opposite direction), and the ever-increasing size and complexity of the rail networks,itis not surprisingthat several coun- tries investigated the possibility of using the rail- way systems to permit rapid evacuation of large numbers of sick and wounded inwarmth,light,and relative comfort,where theycould continue receiv- ing medical and nursing care.The first examples of medical evacuation by rail occurred in 1859,during the Italian War,when large numbers of French casualties were moved via railway.The seriously wounded were transported in baggage cars,the less seriously wounded in pas- senger cars.3 During the American Civil War,many attempts were madeto organize asatisfactory evacu- ation service using railway trains.After many ex- periments,the UnionArmy developed a well-orga- nized ambulance train service,which,as well as carrying the sick and wounded,had facilities to maintain treatment andprovide catering during the ourney.In some of the campaigns,the distance from the front line to the base hospitals was several hundred miles.In 1864,the Army of the Cumber- land River made use of three trains per day to transfer the sick and wounded back to Louisville, Kentucky.The Confederate forces were not so lucky:only irregular service was available,with none of the amenities available to the Union forces.3Owing to the leadership of Jonathan Letterman thechiefmedical officerof the Army of thePotomac, by the end of the American Civil War military medical evacuation was seen as a systematic pro- cess to be carried out by a dedicated corps of spe- cialists under the command and controlof themedi- cal department.Letterman's influence was such that he was able to get theU.S.Congress to enact a law codifying the organization and function of ambulance corps and ambulance trains.?Many of the subsequent developments in military medical evacuation revolved around the technical charac- teristics of the evacuation vehicles,but the correct- ness of Letterman's doctrinal and organizational innovations is still considered beyond dispute.By the second half of the 20th century,aircraft had become the preferred evacuation vehicle in western armies,but use and acceptance came slowly.The first aircraft did not fly until1903;however,the future use of rapid air transport of the sick and wounded had already been conceived by imaginative minds:Anesthesia and Perioperative Care ofthe Combat Casualty·Jules Verne,inhisbookRobertle Conquerant, published in 1854,described the use of an airship to rescue injured and shipwrecked seamen.8·War historians have described the use of hot-air balloons to evacuate the sick and wounded during the siege of Paris during the Franco-Prussian War(1870-1871);un- fortunately,however,this romanticdescrip- tion cannot be supported by fact.9·In the last decade of the 19th century,the Dutch Surgeon General de Mooy described and illustrated his concepts of air evacua- tion (Figure 27-1).Only 7years after the Wrightbrothers'firstflight, two U.S.Army officers had developed an airplane for the transport of casualties but the venture did not receive War Department backing.A second attempt to obtain U.S.Army funding for the con- struction of an airplane to transport the severely wounded was made during a conference in Balti- more,Maryland,only to be followed byan editorial in the following day's Baltimore Sun(23 October 1912)that stated:“Surely the hazard of being se- verely wounded was sufficient without the addi- tional hazard of transportation by airplane.&quot;10 A similar fate followed the first demonstration flight in the United Kingdom,which took place in 1913 and lasted exactly 45 seconds.The surrogate patient's shouts of fear as he slid gently across the wing toward the pusher propeller caused a rapid landing and a complete lack ofinterest by the army general staffwho were present.¹<img src="/media/202408//1724832309.265186.jpeg" />Fig.27-1.Aeromedicalevacuation as envisioned by Dutch Surgeon General deMooy during the late 19th century. Photograph:Reprinted from Vincent A.Le transportdes blesses par avion.Rev Int Croix Rouge.1924;6:720-723.<img src="/media/202408//1724832309.267921.jpeg" />Fig.27-2.Rarely,aircraft were used to evacuate casual- ties during WorldWar I.Reprinted with permission frome<img src="/media/202408//1724832309.2699509.png" />c9o4<img src="/media/202408//1724832309.271723.png" />bulancesin critical care.JRAircraft were used to evacuate casualties during World War I(Figure 27-2),but the first use of an airplane specifically modified for casualty evacua- tion appears to have occurred in 1920 during a British expedition to what is now Somalia.12 The mass transportation of sick and wounded by air first occurred during the Spanish Civil War(1936) and was carried out by the newly formed German Luftwaffe.The Condor Squadrons,flying unheated and unpressurized JunkersJU52s,transported sick and wounded back to Germany in a few hours rather than the days that would have been required for road,rail,and sea transport.13 The resulting improvement in the morale of the sickand wounded were exactly the same as Larrey had described 140 years earlier.14 The full development of German aeromedical evacuation occurred during the early yearsof WorldWarIIand especially during the Russo- German campaign,where the great distances made evacuation by air especially desirable (Figure 27-3).During the fall of 1942,far-sighted U.S.military medical authorities,in recognition of the value of aeromedical evacuation,established three patient categories that wouldjustify trans-Atlantic evacua- tion to the continental United States(CONUS):(1) emergency cases for whom essential treatment was not locally available,(2)casualties whose air evacu- ation the chiefsurgeon deemed a military necessity, and(3)casualties who required prolonged hospital and convalescent care.Nevertheless,by the end of 1943,only 116 patients had been evacuated by air from the European Theater of Operations.By the last year of the European war,from 2,000 to 4,000 casualties per month were being evacuated to CO- NUSby air.This number,although large,needstoMilitary Medical Evacuation<img src="/media/202408//1724832309.277944.jpeg" />Fig.27-3.A German aeromedical staging base in the southern portion ofthe eastern front during 1943.The JU 52s shown here could carry up to 12 litter casualties;their short takeoff and landing capability were impressive (the minimum runway length was about 400 m).The relatively idyllic circumstance shown here was exceptional.More representative of German aeromedicalevacuation was the situation at Stalingrad during the great battlein1942-1943, in which25,000 German casualties were evacuated under appalling weather conditions and in the face of overwhelm- ing Sovietmilitary strength.Reprinted with permission from Carell P.Der Russlandkrieg:Fotografiert von Soldaten [in German].Frankfurt,Germany:Verlag Ullstein GmbH;1967:320-321.be put in perspective;casualties returned by air constituted only about 10%of the total number of evacuees from Europe.The great majority were sent home by ship.15Because of its success in World War II and rapid developments in aviation technology,aeromedical evacuation from the hospital level soon came to dominate all other forms of military medical evacu- ation.The Secretary of Defense directed in Septem- ber 1949 that all evacuation of sick and wounded, bothin peace and in war,shallbe accomplished by air whenever aircraftare available and propermedi- cal treatment can be provided to the patient en route.16 The rationale for this policy,whichremains in effect,is stated in Table 27-1.The various modes of transportation that are used in military medical evacuation should not be thought of as mutually exclusive.In fact,more than one type of evacuation vehicle is commonly needed.The complexity and interrelationofevacu- ation assets was nowhere more obvious than in the European Theater of Operations at the end of World War II,in which evacuation was carried out every using almost every type of land,sea,and air vehicle (Figure 27-4).Although the U.S.Army's experience since World War II has emphasized evacuation by air at all echelons,the number of casualties generated ina high-intensity war and theconditions present in such a war may allow only for ground evacuation.For example,medical plan- ning for a war between North Atlantic Treaty Organization (NATO)and Warsaw Pact countries envisioned the extensive use of hospital trains in addition to tactical medical evacuation flights from the corps communication zone.Military anes- thesia providers need to maintain a broad perspec- tive when thinking about medical evacuation if for no other reason than to ensure that the system is resilient.Althoughairtransportationhasbecome the domi- nant mode of evacuation,its utility is based on a frequently unrecognized assumption;namely,that a forward air base would always be available for use as an evacuation and holding center.The Brit- ishexperiencein the Falklands Warin 1982 showed that this is notalways true.No forward airbase was available initially,which made it impossible to fly treated casualties out of the combat zone.This would have been difficult even if an airfield had been available because the distance between the Falkland Islands and the nearest British airbase,on Ascension Island,is 4,000 miles (6,400 km).The solution to the problem was to evacuate casualties by helicopter to ahospitalship,which then sailed to neutral territory(Uruguay),from where the casual- ties were evacuated by air.17Anesthesia and Perioperative Care ofthe Combat CasualtyTABLE 27-1ADVANTAGES OF AEROMEDICAL MEDICAL EVACUATION<table><tr><td>Advantage</td><td>Rationale</td></tr><tr><td>Speed</td><td>The“Golden Hour”of resuscitation can be better utilized by rapid and safe air transport of the casualty.The value of rapid evacuation to a Level-1 trauma center has been well-</td></tr><tr><td>Range</td><td>demonstrated in civilian medicine.Transport of casualties over long distances in a relatively short period of time allows fewer tertiary centers to support several units.</td></tr><tr><td>Trafficability</td><td>Rotor-wing aircraft can pick up patients in relativelyinaccessible areas and transport them quickly and safely.The minimal landing requirements provide this feature.</td></tr><tr><td>Flexibility</td><td>A casualty can be airlifted quickly to that medical installation where appropriate special- ized care may be available,thereby bypassing unnecessary delays</td></tr><tr><td>Comfort and Morale</td><td>Because of the speed and comfort of flight,the soldier knows that if injured,he can betransported to the appropriate medical treatment facility quickly and in stable condition.</td></tr><tr><td>Economy of Resources</td><td>Because one large hospital is able to accommodate several battle areas,fewer facilities need to be set up.</td></tr></table>Thehospitalship was obtained by converting the cruise linerSS Uganda,the conversion beingcarried outin only 4 days.The vessel,which was equipped with a helicopter landing pad,full hospital facili- ties,and an intensive care unit,was only 15 min- utes'flying time from the land battles.Interna- tional Red Cross regulations required that once on board the hospital ship,all casualties had to be evacuated from the war zone.Their repatriation required the good offices of the Uruguayan authori- ties,who permitted their transfer by sea (in small survey vessels),over 1,500 km from the Falkland Islands to Montevideo,for onward air transporta- tion to the United Kingdom.Five hundred eighty casualties were evacuated by this route.17The expe- rience of the SS Uganda constitutes one of the few recent instances in which a hospital ship has been used asaevacuation vehiclein addition to function- ing as a hospital.Much more common is the use of hospital ships as deployable hospitals.The British experience in the Falkland Islands hasled to a reevaluation of the role ofhospital ships in any future conflict,resulting in the U.S.Navy's converting twosupertankersinto thehospital ships Comfort and Mercy,two 1,000-bed hospitals with full facilities.However,few countries can afford theluxury ofmaintainingpermanent,fully equipped hospital ships.A less expensive system has been developed,whereby hospital facilities suchaswards,operating theaters,radiographic units,laborato- ries,and intensive care facilities have been modu- larized,based on the International Standards Organization's (ISO's)standard container.The number of units can be varied as required and rapidly installed in any suitable ship.The ships must have unobstructed deck space, such as is usually found on fleet auxiliaries,tank- landing ships,or roll on-roll off merchant ferries. The great advantage of the modular system is that the vessel can carry out its ordinary task until it is required formedical duties.Thebenefits offered by the Rapid Deployment Hospital Ship program are low cost,a dual role for the ship,extremely rapid conversion into the war role,a controlled hospital environment,and the possibility that any of the modules can be transferred to land,if required. This excellent,low-cost facility was used when a British Naval Auxiliary vessel was converted into a 100-bed facility in a short time and sailed to the Persian Gulfduring thehostilities there(1990-1991). 	In describing the evolution of military medical evacuation in the 20th century,evacuation from forward hospitals to hospitals in the communica- tion zone or CONUS has been emphasized almost exclusively.However,regardless of how success- fully this link in the evacuation chain functions,it remains totally dependent on the casualty's first having been evacuated from the battlefield.EvenMilitary Medical Evacuation<img src="/media/202408//1724832309.305386.jpeg" />aBy ambulance or hospital trainb By ambulance,hospital train,orairplaneFig.27-4.This cartoonshows howevacuation was carried outin and from theEuropeanTheater ofOperationsinWorld War II.The built-in redundancy allowed for maintenance of the casualty flow even if the activity of one form of evacuation wasimpaired(eg,when aeromedical evacuation washindered by bad weather).Itis important to recognize that evacuation in and from the theater of operations depends totally on the casualty's arriving at this echelon after successful evacuation from the unit,division,and corps levels.The symbols indicate army-level,general,and evacuation hospitals.HU:holding units.Reprinted from Cosmas GA,Cowdrey AE.Medical Seroice in the European Theater ofOperations.Washington DC:Center of Military History,US Army;1992:335.<img src="/media/202408//1724832309.334225.jpeg" />Anesthesia and Perioperative Care of the Combat Casualtywith the fieldambulances of Larrey and Letterman, thecasualty would firsthave to be taken to a collec- tion point from where he could be removed from the battlefield.Extracting casualties from the battle- field,frequently while under enemy fire—the most difficult,arduous,and dangerous segment of the evacuation chain—remained the province of med- ics,litter bearers,and nonmedical soldiers,who all depended on human muscle power to move the casualty.The advent of mechanized warfare in World WarIImade possible analternative approach, namely,the use ofequipment:first,armored fight- ing vehicles;and second,small,fixed-wing aircraft and helicopters.The latter had a revolutionary effect on evacuation because it made possible the speedy transportation of casualties directly from the scene of wounding on the battlefield to a surgi- cal hospital.Helicopter evacuation from the battlefield first occurred in1944in Burma,butfirst assumed promi- nence in the Korean War,during which approxi- mately 17,700 casualties were evacuated from the battlefield to hospitals.18 Although more than 300,000 casualties were evacuated from Korea to Japan during the Korean War,the true value of air evacuationwas in the timely pick-up and transport of the soldier from the point of wounding to the point where he was seenby a medicalofficer.It was widely recognized by medical authorities,both military and civilian,that timely evacuation,to- gether with the use of whole blood and antibiotics, were the three factors responsible for the low mor- talityduring the Korean War.During the Vietnam War,between 850,000 and 900,000 allied military personnel and Vietnamese civilians underwent aeromedical evacuation.At least 90%of all hospitalized U.S.Army battle casu-alties were evacuated by helicopter at one time or other during their treatment.18 There can be no doubt that the helicopter,by making unnecessary many long and difficult litter carries as well as uncomfortable trips in ground ambulances,made life much more tolerable for both casualties and medics (Figure 27-5).Nevertheless,helicopterevacuation of casualties directly from the battlefield was not without draw- backs.For example,when compared with fixed- wing aircraft,helicopters have limited operational ranges.On an extensive battlefield suchas charac- terized thePersianGulfWar,directhelicopterevacu- ation from the site of injury to the hospital level is usually impractical.In addition,darkness and weather conditions at times interfere with aeromedical evacuation.More importantly,heli- copter evacuation from the battlefield can be very dangerous.It hasbeen estimated that one third of all air ambulance pilots in the Vietnam War sus- tained either battle or nonbattle injuries,and medi- calevacuationhelicopterssustained more than three times more battle damage than helicopters used in combat and combat support missions.18 Although regulationsinitially precluded making casualty pick- ups from landing zones that were subject to enemy fire,thisbecame commonplaceinboth the Korean and Vietnam wars.The heroism ofhelicopter crews made possible the evacuation of casualties that in many instances,in retrospect,seems impossible.Even so,helicopter evacuation from the high- intensity battlefield is probably suicidal.In fact, U.S.Army regulations do not foresee casualty ex- traction byhelicopter occurring forward of the bat- talion aid station when enemy air-defense artillery capabilitiesare substantial;thus,theneed forevacu- ation vehicles capable of functioning far forwardFig.27-5.A scene from the Somalia peacekeeping operation.A casualty is beingremoved from a UH-1 medi- cal evacuationhelicopter whilea UH- 60 hovers in the background.The latter is now the US Army's primary air ambulance,replacing the former, which has served with distinction since its introduction in 1959.The UH-60 has greater range and speed, and superior aivonicscompared with the UH-1 but,suprisingly,can carry no more casualties.Photograph:Pub- lic Affairs,Officeof The SurgeonGen- eral,US Army.Military Medical Evacuation<img src="/media/202408//1724832309.4082088.jpeg" />Fig.27-6.Evacuation during an armored battle fought in central Russia during summer,1943.The armored unit's medical officer rode into battle in the tank shown on the left and was accompanied by an armored personnel carrier, which was used to evacuate the casualty.Firstaid and preparation of the casualty for evacuation tookplacein the open Although the casualty was protected from small-arms fire and fragments from shells during evacuation,the small internal volume of the armoredpersonnel carrier precluded effective ongoing care.Futhermore,the separation of the physician and the casualty during evacuation no doubt resulted inincreased mortality and morbidity.Reprinted with permission from PielkalkiewiczJ.Unternehmen Zitadelle [in German].Bergisch Gladbach,Germany:Gustaf Lübbe Verlag GmbH;1983.under enemy fire.2(p⁴-12)The precedentfor the use of armored fighting vehicles for this purpose dates from early in World War II,when German armored formations used half-track vehicles for casualty evacuation(Figure27-6).More recently,many other armies have used armored personnel carriers forevacuating casualties under enemy fire.The Israe- lis have even used their main battle tank—the Merkava—for this purpose.The Merkava's engine is in the front,which leaves a space in the rear— accessed by an armored door—that can be used for carrying several casualties.LOGISTICAL AND OPERATIONAL ASPECTSThe schematic diagram that is part of the front matter ofthis bookshowsthe organizationforevacu- ation as it existed in the U.S.Army at the time of publication.For purposes of this chapter,the sys- tem used to evacuate sick and wounded soldiers will be studied in three segments:(1)the unit (ie,the medical platoon)and the division level,(ie,the medical company or medical battalion,which usu- ally have no surgical capabilities);(2)the corps level and the communication zone,which contain the deployable hospitals;and (3)the domestic sys- tem,which is operated by the U.S.Air Force.Unit and Division LevelsEvacuation at the unit level can be by ground or by air.The type of vehicle used depends on the warfighting scenario.In a high-intensity war,it is likely that 90%of casualty evacuation will be byground,with the remaining 10%by air(—RFB, personalobservation,1994).In alow-intensity war, mostevacuation canbe expected to be by air.Evacu- ation at the unit level is regulated by the battalion surgeonor the medical company commander;atthe division level,by the division medical operations center.2(p4-2)Ground EvacuationAs previously indicated,aerial transport may not be feasible because of enemy action.Fur- thermore,bad weather,darkness,and distance may preclude aeromedical evacuation.Ground ambu- lances may be used at these times.These ambu- lances,which are organic (ie,intrinsic;included in the Table of Organization and Equipment)to the U.S.Army Medical Department units that are re- sponsible for transporting the sick and wounded,Anesthesia and Perioperative Care ofthe Combat Casualtyhave the basic supplies and are staffed with ambu- lance personnel qualified in basic emergency medi- cal care and treatment procedures.An ambulance crew consists of a driver and an additional soldier, both of whom are medical aidmen.Current ground ambulances include the following vehicles²KpP⁰-1-10-16.·M1010 truck ambulance,1/4 ton 4x4.This truck is designed to transport the sick and wounded and is the standard field ambu- lance of medical units at the division and higher-level units where suitable roads ex- ist.The patient compartment is separated from the remainder of the vehicle and has a heater and a surgical light.The capacity is 4 litter patients,or 8 to 10 ambulatory pa- tients,or a combination of litter and ambu- latory patients (eg,2 litter and 5 ambula- tory patients).·High-mobility,multipurpose,wheeled ve- hicle(HMMWV,M996 and M997)truck ambulance,4x4,armored tactical vehicles The HMMWVis designed tobeused cross- country and over alltypes of terrain.De- pending on the configuration,thevehicle can carry 2 to 4 litter patients,or 6 to 8 ambula- tory casualties,or a mixture of litter and ambulatory casualties.These vehicles can be modified for operation ina nuclear,bio- logical,or chemical warfare environment.·M113 carrier,personnel,full-tracked,ar- mored.The M113 can carry up to 10 ambu- latory or 4 litter patients.The M792(Gamma Goat),M170,and M718 evacua- tion vehiclesare being phased out of the U.S.Army's inventory.Any military vehicle may be adaptedfor carrying patients as the situation allows,but safety and stability during transport are important priori- ties that need to be satisfied by any putative ambu- lance.Air EvacuationAn assigned mission of the U.S.Army is to pro- vide air transportation for the sick and wounded within the combat zone.The major objective of air transportation is the expedient delivery of the casu- alty to the care level necessary for survival.The flexibility andrapiddeployment ofairservices make this an optimal method of delivery.Air transport involves the use of either fixed-or rotor-wing air- craft.Organization ofU.S.Army Air EvacuationA soldier injured in a forward area may initially receive first aid from an aidman.Then the soldier may be transported by ground to the battalion aid station,where theinjury is reassessed;ifevacuation is necessary,it is the U.S.Army's responsibility to provide appropriateground or airevacuation.The atter is usually provided by the medical air ambu- lance company.The medical company's air ambu- lance is normally assigned to the corps medical brigade and is attached to the medical evacuation battalion for command and control.2(p3-7)The capabilities of the medical air ambulance company includeaeromedicalevacuationofcritically wound- ed or other patients;·extrication and then air evacuation of per- sonnel from crashed aircraft;·emergency aid at air-crash sites,in-flight medical treatment,and surveillance of pa- tients en route to treatment facilities;<img src="/media/202408//1724832309.424505.jpeg" /> expeditious delivery of medical personnel and material tomeet emergency treatment requirements within a combat zone;and·in-flightemergency medical careThe core of the air ambulance company is its air ambulance platoon.Military physicians need to be aware of the composition and skill level of this platoon.Each consists of a platoon leader,two section leaders,nine evacuation pilots,one platoon sergeant,sixair ambulance aidmen,six crew chiefs, and one voice-radio operator.Each platoon is au- thorized six UH-60A helicopters.Each helicopter has an assigned crew consisting ofa crew chief,two pilots,and an air ambulance aidman.All are profi- cient in emergency medical treatment.Although each air ambulance has a capacity for six litter patients or nine ambulatory patients(the UH-1),or four litter and seven ambulatory patients(the UH- 60A),the combat load for each is three litter and four ambulatory patients.2(p10-27)The situation may occur when nonmedical air- craft such as the U.S.Army's CH-47 Chinook will be used for evacuation at the division level.This helicopter can carry up to 24 litter patients.Only approved and tested equipment may be taken aboard aircraft,and each type of aircraft has its own list of approved equipment.Medical per- sonnel should consult with the crew chief or senior medic of the particular aeromedical evacuationMilitary Medical Evacuationambulance to ascertain what equipment is pres- ently available and approved.Air Ambulance OperationsAir ambulances are used as far forward as pos- sible andas the numbersofcombatcasualties allow. Ambulances should be used only if the landing zone is both free of hostile fire and secure.If it is not,the pilot must be notified.The base of opera- tions must be located and operated so that it can respond as quickly as possible when there are casu- alties on the battlefield.In the absence of clear guidelines as tothe casualty's destination,the pilot is the final authority.All medical officers of deployable units should know how to arrange aeromedical evacuation.FM 8-10-6 should be consulted for a detailed descrip- tion of the official procedure;a brief overview fol- lows.Requests for air ambulance evacuation must contain concise,accurate,and reliable information so that appropriate equipment can be provided and flights planned.The commander of the air ambu- lance team supportingthe division decides whether to accept the mission,based on meteorological con- ditions or the availability of aircraft.All U.S.Army aeromedical evacuation requests should provide information in thesequence provided in FM 8-10-6 (Exhibit 27-1).Assignment of Medical Evacuation PriorityFM 8-10-6 specifies the following categories of precedence and the criteria used for their assign- ment:PriorityI—URGENTisassigned to emergency cases that should be evacuated as soon as possible and within a maximum of 2 hours to save life,limb,or eyesight;to prevent complications of serious ill- ness;or to avoid permanent disability.Priority IA—URGENT-SURG is assigned to pa- tients who must receive surgical intervention far for- ward to save life and stabilize for further evacuation Priority Ⅱ—PRIORITY is assigned to sick and wounded personnelrequiring promptmedical care. This precedence is used when(a)the individual should be evacuated within 4 hours or his medical condition could deteriorateto sucha degree that he will become an URGENT precedence,or(b)require- ments for special treatment are not available locally, or(c)will sufferunnecessary pain or disability.Priority Ⅲ—ROUTINE is assigned to sick and wounded personnelrequiringevacuation but whose condition is not expected to deteriorate signifi-<table><tr><td>EXHIBIT 27-1SEQUENCE OF INFORMATIONREQUIRED IN U.S.ARMY AERO-MEDICAL EVACUATION REQUESTSLINE 1:Location of pick-up siteLINE2:Radio frequency,call sign and suffixLINE 3:Number of patients by precedence,as described in FM 8-10-6(p7-1)LINE4:Special equipment required (eg, ventilator)LINE 5:Number of patients and type of injury LINE 6:Security of pick-up siteLINE 7:Method of marking pick-up site LINE 8:Patient nationality and status LINE 9:Nuclear,biological,and chemicalcontaminationAdapted from Department of the Army.Field Manual 8- 10-6.Medical EoacuationinaTheaterofOperations.Washing- ton DC:Headquarters,DA;31 October 1991:pp 7-3-7-5.</td></tr></table>cantly.The sick and wounded in this category should be evacuated within 24 hours.Priority IV—CONVENIENCE is assigned to pa- tients for whom aeromedical evacuationisa matter of medical convenience rather than necessity.2(p⁷-1)Civilian Approaches to the Assignment of Evacuation PriorityThe assignment of evacuation priorities accord- ing to FM 8-10-6 is,by its very nature,subjective. In an effort to bring objectivity to the determination of the need for helicopter evacuation to a trau- ma center,civilian emergency medical systems have adopted the use of triage scoring systems. The civilian approach needs to be understood by military anesthesiologists because a modifica- tion may be applicable to military medical evac- uation:·The Trauma Score(Exhibit 27-2)is a com- posite that includes measures of the statusof the cardiovascular,respiratory,and cen- tral nervous systems.(It incorporates the<table><tr><td><table><tr><td>EXHIBITTRAUMA</td><td>27-2SCORE</td><td>USEDIN</td><td>CIVILIAN</td><td>EVACUATION</td></tr></table>Trauma Score ComponentValueA.Respiratory RateNumber of respirations in 15s,multiplied by 410-24 25-35 	&gt;35 &lt;100B.Respiratory EffortNormalNormalShallowRetractiveShallow—markedly decreased chest movement or airexchangeRetractive—use of accessory muscles or intercostalretractionC.Systolic Blood PressureSystolic cuff pressure,either arm,auscultate or palpate&gt;90 70-90 50-69 &lt;50No carotid pulse0D.Capillary RefillNormal—forehead,lip mucosa,or nail-bed colorNormalDelayed Nonerefills in 2 sDelayed—more than 2 s of capillary refillNone—no capillary refillE.Glasgow Coma Scale(GCS)Total Glascow Coma Scale PointsValue1.Eye OpeningSpontaneous14-1511-138-105-74321To yoiceTo painNone2.Verbal Response54321OrientedConfusedInappropriate wordsIncomprehensible wordsNone3.Motor ResponseObeys commands654321Purposeful movement (pain)Withdraw(pain)Flexion(pain)Extension(pain)NoneTotal GCS points (1+2+3)(Total</td><td>Points Score43210A 100B. 43210C. 210D. Score5432 E. Trauma Score points A+B+C+D+E)</td></tr><tr><td colspan="2">Reprinted with permission from Champion HR,Sacco WJ,Carnazzo AJ,et al.Trauma score.Crit Care Med.1981;9:672.</td></tr></table>Glasgow coma scale as its central nervous system component.)The bestfeature of the Trauma Score is that it measures the physi- ological state at the scene of the injury. Patients who require prompt diagnosisand definitive care at a Level 1 trauma center are those with a score of 12 or less.19·The CRAMS scale was developed by S.P. Gormican in 1982 and modified by T.P. Clemmerin1985(Exhibit 27-3).20 Itisasimple and easy scale to remember,with the letters of the acronym representing circulation,res- piration,abdomen,motor,and speech.<table><tr><td colspan="2">EXHIBIT 27-3MODIFIED CRAMS SCALE USED IN CIVILIAN MEDICAL EVACUATION</td></tr><tr><td colspan="2">Circulation2:Normal capillary refill and blood pressure &gt;100 mm Hg systolic1:Delayed capillary refill or blood pressure 85-99 mm Hg systolic0:No capillary refill or blood pressure&lt;85 mm Hg systolicRespiration</td></tr><tr><td>2:Normal1:Abnormal(labored,shallow,or 0:Absent</td><td>rate&gt;35)</td></tr><tr><td colspan="2">Abdomen2:Abdomen and thorax not tender1:Abdomen and thorax tender0:Abdomen rigid,thorax flail,or deep penetrating injury to either chest orabdomenMotor2:Normal(obeys commands)1:Responds only to pain,no posturing 0:Postures or no responseSpeech2:Normal(oriented)1:Confused or inappropriate0:Unintelligible or no sounds	 Total CRAMS Score</td></tr><tr><td colspan="2">Reprinted with permission from ClemmerTP,Orme JF Jr,ThomasF,etal.Prospectiveevaluation of theCRAMS scale for triaging major trauma.JTrauma.1985;25:189</td></tr></table>Military Medical EvacuationRecommended equipment for civilian helicopter evacuation is shown in Exhibit 27-4.A simplified triage flow sheet (Figure 27-7)and a recommenda- tion for helicopter transportatall times(Exhibit27- 5)²¹are alsoincluded to allow some familiarity with civiliandecision making.Additional recommenda- tions have been set forth for the transport of the critically ill patient and have been reviewed and ap- proved by The Association of Air Medical Service.2Corps and Communications Zones:Zone of theInteriorMuchof the medical evacuation thatoccurs atthe corps level and above will involve the U.S.Air Force.However,the corps level medical evacua- tion battalion has as one of its missions the task of evacuating casualties from the division to the corps level,and does this by using the army's ground or air assets.Evacuation from the division is regulated by the division Medical Operations Center and the medical group Medical Regulations Officer.2(p⁴-2) Evacuation from the corpslevel to the communica- tion zone and higher is the mission of the Military Airlift Command of the U.S.Air Force.Medical regulating at this level proceeds from the patient administrator of a given hospital to the medical group and medical brigade Medical Regulating Office to the theater-levelJoint Medical Regulating Office.Medical regulating for evacuation from the communications zone to the zone of the interior is carriedoutby the Armed Services Medical Regulat- ingItOifsfi<img src="/media/202408//1724832309.452994.png" /><img src="/media/202408//1724832309.455366.png" />.portant that military anesthesiologists recognize that when the casualty initially enters the U.S.Air Force's medical evacuation system,he will be ata Mobile Aeromedical StagingFacility(MASF). The function of this unit is to collect casualties, not to provide treatment.Physicians are not as- signed to a MASF and casualties should not be sent there unless they are in stable condition.Further- more,the MASF doesnot have aholding capability; patients are not to remain there longer than 6 hours.2(p6-9)Tactical Evacuation SystemThe tactical evacuation system provides for the airliftof patients within thecorps leveland from the corps level to the communication zone.Most of these casualties will have had initial surgery and should be in stable condition.U.S.Air Force guid- ance indicates that mission duration will notexceedAnesthesia and Perioperative Care of the Combat Casualty<table><tr><td colspan="2">EXHIBIT 27-4RECOMMENDED CIVILIAN HELICOPTER CHECK LIST</td></tr><tr><td>In Side Wall Blue Pouches:1 pairwrist restraints1 roll 2-in.cloth tape2 oralairways(small,medium)130-mL syringe110-mL syringe2 pairs eyeglassesMasks and glovesIn FrontWall Pockets:2 survival kits2 life vestsDoppler flow probe and acoustic coupler2 lithium-powered batteriesObesity blood-pressure cuffLarge adult blood-pressure cuffPassenger guideOn Side Wall:Suction cannister with suction tubing and yankeur2 oxygen regulatorsPersonal mask resuscitation bag,with maskIn Clam Shell:2 head rollsCervical collars(small,medium,large) 1 spider strapPediatric immobilizer with pumpIn Airway Seat:Large survival kit1life vestIn Side Seat Drawer:4 D-cell batteries2 reflective vests1 syringe pump1 syringe pump charger2 spare stretcher brackets1 flashlight1 L normal saline500 mL TridilCharcoal and ipecac syruptFoam ear plugsCharger for PROPAC+monitor and pulse oximeter</td><td>Between Bench and Side Seat:Military antishock trousers bagIn Side Rear Pouch:1 trauma dressing1 sterile drape2 reflective vests1 camp lightUnder Bench Seat:LinenPneumatic shock garments,adult and pediatric, with pumpClipboard with flight chartsUnder Side Seat:Elastic bracket for lithium-powered batteryOn Wall Next to Side Seat:Backup stretcherKED extraction splintSScoop stretcherBlue interhospital patient-attendant bag Red scene bagBehind Side Seat:3 oxygen tanksWith Stretcher:Oxygen tank and regulatorPROPAQmonitor with cables and cuffAlso Aboard Helicopter:1 spare headset2 fire extinguishersPortable,free-standing suction unitISuction kits and 1 yankeurCharger for lithium-powered battery</td></tr><tr><td colspan="2">Nitroglycerin in1,2,3-propanetrioltrinitrate,manufactured by Du Pont Multi-Source Products,Garden City,NY tSyrup of Ipecac,manufactured by Roxane Laboratories,Inc,Columbus,Oh+Manufactured by Protocol Systems,Inc,Beaverton,OreSKendrick Extraction Device,manufactured by Medix Choice,Santee,CalifIPortable:Continuous and Programmable Intermitent SuctionSystem,Model326/326M,manufactured byImpact Instru mentation,Inc,West Caldwell,NJ</td></tr></table><img src="/media/202408//1724832309.4650922.png" /><img src="/media/202408//1724832309.467415.png" />Rearward displacement of front axleMilitary Medical Evacuation<img src="/media/202408//1724832309.469077.jpeg" />Stage 1Measure vital signs andlevel of consciousnessGlasgow coma scoreSystolic blood pressure Respiratory rate&lt;13 or&lt;90 or&lt;10 or&gt;29Yes NoTransporttotrauma centerStage 2 Assess anatomy of injuryand mechanism of injuryPenetrating injury to chest,abdomen,head,neck,and groinTwoor more proximal long-bone fractures<img src="/media/202408//1724832309.472095.png" />i<img src="/media/202408//1724832309.4736462.png" />wmabyination with burns of&gt;15%of the body surface or of the face orFlail chestEvidence of high-speed impact:Falls of 20 ft or moreCrash speed 20 mph or more;20 in.deformity of automobilePassengercompartment intrusion 15 in.on patient side of automobile;20 in.on opposite side of automobileEjection of patientRollover of automobileDeath of occupant in same automobilePedestrian hit at 20 mph or moreYes NoTransporttotraumacenterStage 3Age&lt;5 or&gt;56Known cardiac or respiratory disease (which lower the threshhold of severity requiring care in a trauma center)YesNoConsidertaking to trauma centerfor injury of moderate severityReevaluatefollowing consultaion withappropriate specialistsWhen in doubt,transport to a trauma centerFig.27-7.Civilian triage decision scheme.In stage 1,if easily determined clinicalindicessuch as the Glasgow coma score, systolic blood pressure,and respiratoryrate are abnormal,the patient should be flown directly to a trauma center.Stage 2isimplemented in patientsin whom these indices are not grossly abnormal.The anatomical location of the injury andits mechanism are used as discriminators.Instage3,extremes ofageand theknownpresenceofcardiopulmonary diseaseare used as further triage discriminators.Adapted with permissionfrom Champion HR.Helicopter triage.Emerg Care Q.1986;2:13-21.Anesthesia and Perioperative Care ofthe Combat Casualty<table><tr><td><img src="/media/202408//1724832309.47793.png" />EXHIBIT 27-5SIMPLIFIED CIVILIAN EVACUATION POLICYA helicopter should be used for patient trans- port under any of the following conditions:Urban and suburban environmentsTransport time to the trauma center&gt;15 min by ambulanceAmbulance transport impeded by access to oregress from the accident scenePresence ofmultiple casualtiesRural environmentTime to local hospital via ambulance&gt;time totrauma center via helicopterWilderness rescue	Reprinted with permission from Champion HR.Heli- coptertriage.EmergCare Quart.1986;2:20.</td></tr></table>4 hours.The mostcommonly used aircraftis the C- 130 Hercules (Figure 27-8).2p¹0-45)The C-130 is a long-range,high-wing,four turboprop-engine air- craft.The fuselage is divided into the cargo com- partment and the flight deck.It can be fully pres- surized,heated,and air conditioned.The C-130 can maintain a sea-level cabin pressure at an alti- tude up to 19,000ft and an 8,000-ft cabin pressure at<img src="/media/202408//1724832309.481246.jpeg" />Fig.27-8.A C-130 Hercules taking off somewhere in the Kuwaiti Theater of Operations during the Persian Gulf War.The original design of the C-130 dates from 1951. The rugged construction of these aircraft allows them to use unprepared runways,as are found forward on the battlefield.Photograph:Defense Audio-Visual Agency, Still Media Depository,Washington,DC.an altitude of 35,000 ft.It can land and take off on runways as short as 600 m,a capability that allows for rapid transportation of personnel and equipment to and from the battlefield.The C-130 can readily be configured for aeromedical evacua- tion by using seat and litter provisions stowed in the cargo compartment,but military anesthesia providers should not expect to find extensive re- sources available for treatment.Depending on in- herent equipment and the model of the aircraft, it can hold a maximum of 74 litter patients,92 ambulatory patients,or various combinations(Fig- ure 27-9).Strategic Evacuation SystemThe missionof the strategicevacuationsystemis toprovide controlled evacuation of stable patients to medical treatment facilities that are located out- side the theater of operations—frequently in CO- NUS.U.S.Air Force guidance on mission duration<img src="/media/202408//1724832309.4862132.jpeg" />Fig.27-9.This photograph,taken during an exercise in 1980,shows theextremely tight space available for indi- vidualcasualties.Thespace and thesparse medicalequip- ment provided markedly limit the provision of in-flight medical care.Photograph:Defense Audio-Visual Agency Still Media Depository,Washington,DC.<img src="/media/202408//1724832309.488254.jpeg" />Military Medical Evacuation<img src="/media/202408//1724832309.490123.jpeg" />Fig.27-10.The C-141Starlifter(a)andits loadingramp(b).This aircraft was the mainstay of the US AirForce's strategic aeromedical evacuation system during both the Vietnam and the Persian Gulf wars.Photographs:Courtesy of Lieutenant Colonel Charles Beading,MD,Medical Corps,US Air Force,Flight Surgeon,Uniformed ServicesUniver- sity of the Health Sciences,Bethesda,Md.is 7 to 14 hours.The aircraftcurrently used is the C- 141 Starlifter (Figure 27-10).2(p10-46)The C-141 is a long-range,high-speed,high-altitude aircraft de- signed for the airlift of combat support equipment, troops,or aeromedical evacuation patients.It is powered by four jet engines,cruises at 550 mph atan altitude of 30,000 ft,and has a range of 5,250 miles.When used for aeromedical airlift,a self- contained comfort pallet canbe placed in the forward section of the cargo compartment.Conditionsaboard a typical strategic aeromedical evacuation flight dur- ing the Persian Gulf War era are shown in Figure<img src="/media/202408//1724832309.493769.jpeg" />Fig.27-11.In-flight conditions for casualties aboard a C-141 during a strategic aeromedical evacuation.Access to patients and the availability of medical equipment are superior to that on the C-130.Photograph:Courtesy of Lieutenant Colonel Charles Beading,MD,Medical Corps,US Air Force,Flight Surgeon,Uniformed ServicesUniver- sity ofthe Health Sciences,Bethesda,Md.Anesthesia and Perioperative Care of the Combat Casualtya<img src="/media/202408//1724832309.497123.jpeg" /><img src="/media/202408//1724832309.4988558.jpeg" />bFig.27-12.The C-9 Nightingale (a),a modified version of the commercial DC-9 and the only US Air Force aircraft especially designed for aeromedical evacuation.(b)Theloadingramp.Photographs:Courtesy of Lieutenant Colone Charles Beading,MD,Medical Corps,US Air Force,Flight Surgeon,Uniformed Services University of the Health Sciences,Bethesda,Md.27-11.Maximum capacity of the aircraft is 103 litters or 147ambulatory patients,or various combi- nations of litter and ambulatory patients.The con- ditions are much better than in the C-130.Patients are not overcrowded,hot meals are provided,and the cabin temperature is better controlled than in tactical aircraft.Oxygen and electrical outlets per- mitthe use ofcomplexmedicalequipmentenroute. However,dehydration may occur becausethe flights are long and the ambienthumidityis low (5%-30%). There has been recurrent interest in configuring and outfitting a small number of C-141s as flying intensive care wards.Domestic Aeromedical Evacuation SystemThe U.S.Air Force's daily system of flights within CONUS has flight crews and aircraft dedicated to aeromedical evacuation of military casualties.The aircraft currently usedis the C-9Nightingale,which is amodified version of the commercialDC-920p10-45) TheT-tailed aircraftis poweredby twin,aft-mounted jet engines and cruises at 500 mph.Its range ex- ceeds2,300 miles.TheC-9 is the only U.S.Air Force aircraft specifically designed for aeromedicalevacu- ation.An integral folding ramp enables efficient enplaning and deplaning of litter patients (Figure 27-12).The C-9 can hold a maximum of 40 litter patients,40 ambulatory patients,or a variety of combinations of litter andambulatory patients(Fig- ure 27-13).The environment on board is compa- rable to first-class accommodations on a commer- cial airline.Most specialized equipment available ona hospital ward can be provided on aC-9,includ- ing isolation and humidity control.Althoughthe domesticsystemisinoperationdaily, it is during emergencies,when military casualties of accidents and disastersrequire evacuation to special- izedhospitals withinCONUS,that its functionis most cearly illustrated,as in the following incident.The airforce's domestic aeromedical evacuation system was activated inMarch 1994 after two army training planes(a four-engine turboprop C-130 Hercules transport plane and a single-engine F- 16D)crashed and burned while attemptingto land at Pope Air Force Base,North Carolina.Twenty- three paratroopers died and 83 others sustained burns or other injuries in the accident.The severely burned survivors were aeromedically evacuated to the burn center at Brooke Army Medical Center, Fort Sam Houston,San Antonio,Texas.3While the injured werebeing triaged and treated at Womack Army Medical Center,Fort Bragg,North Carolina;[civilian hospitals in Fayetteville and Chapel Hill];and Portsmouth [Virginia]Naval Hospital;the Aeromedical Evacuation Coordina- tion Center(57th Aeromedical Evacuation Squad- ron)at Scott Air Force Base(AFB),Illinois...was dispatchingtwo C-9Asand medical crewmembers to Fayetteville.In the meantime,the Air Education and Training Command (Randolph AFB,San Antonio [Texas]) provided a twin-jetT-43 A...tofly a burn team from Brooke Army Medical Center to Pope AFB.[T]he first C9-A departed Pope AFB the following morning for Kelly AFB,San Antonio,with 11 pa- tients on litters,nine of whom were on ventilators. All had second-and third-degree burns covering from 30%to 80%of their bodies....The second C- 9A made the flight about 5 hours later with nine<img src="/media/202408//1724832309.5092502.jpeg" />Military Medical Evacuation<img src="/media/202408//1724832309.5130482.jpeg" />Fig.27-13.(a,b,andc)Patient condi-tions aboard the C-9 Nightingale.Photographs:Courtesyof LieutenantColonel Charles Beading,MD,Medi-cal Corps,US Air Force,Flight Sur-geon,Uniformed Services Universityof the Health Sciences,Bethesda,Md.<img src="/media/202408//1724832309.515685.jpeg" />Anesthesia and Perioperative Care of the Combat Casualty<table><tr><td>EXHIBIT 27-6U.S.AIR FORCE CLASSIFICATION OF PATIENTS SCHEDULED FOR AEROMEDICAL EVACUATION<img src="/media/202408//1724832309.517967.png" />Class 1.Neuropsychiatric PatientsIA.Severe psychiatric litter patients requiring the use of restraining apparatus,sedation,and close supervision at all times.IB.Psychiatric litter patients of intermediate severity requiring tranquilizing medication or sedation, not normally requiring the use of restraining apparatus,but who react badly to air travel or who may commit acts likely to endanger themselves,others,and/or the safety of the aircraft.Restrain- ing apparatus should be available for use.IC.Psychiatric walking patients of moderate severity who are cooperative and who have proved reliable under observationClass 2.Litter Patients(Other Than Psychiatric)2A.Immobile litter patients unable to move about of their own volition under any circumstances. 2B.Mobile litter patients able to move about of their own volition in an emergency.Class 3.Walking Patients (Other than Psychiatric)3A.Nonpsychiatric and nonsubstance abuse patients who require medical treatment,assistance,or observation en route.3B.Recovered patients who are returning to their units and require no medical attention en route. 3C.Ambulatory drug or alcohol substance-abuse patients.Class 4.Infant Category4A.Infants under 3 years of age,occupying a seat or in a bassinet orcar seat secured in an ambulatoryseat.4B.Recovered infants under 3 years of age,occupying a seat or in a bassinet or car seat secured in anambulatory seat.4C.Infants in an incubator.4D.Infants younger than 3 years ofage on a litter.4E.Outpatientsunder 3 years of age on a litter for comfort.Class 5.Outpatient Category5A.Ambulatory outpatients,non psychiatric and nonsubstance abuse,who are traveling for anoutpatient visit and do not require a litter or medical assistance in flight.5B.Ambulatory drug-or substance-abuse outpatients going for treatment.5C.Psychiatric outpatients going for treatment.5D.Outpatients on a litter for comfort or safety.5E.Returning outpatients ona litter for comfort or safety.5F.Other returning outpatientsClass6.Attendant Category.6A.Medical attendants,either physician,nurse,or technician,who are assigned to give specialized medical treatment or nursing care to a particular patient.6B.Nonmedical attendants,either relatives or friends,who may assist with the patient's care and whomay also require support.Sources:(1)Department of the Army.Field Manual 8-10-6.Medical Evacuation in a Theater of Operations.Washington DC: Headquarters,DA;31October 1991:pF-1.(2)Department of the Air Force.Physicians'Rolesand Responsibilities in Aeromedical Evacuation.Washington,DC:Secretary of the USAF;1995:in press.Air Force Joint Manual 41-306.</td></tr></table><img src="/media/202408//1724832309.5232651.png" />)metric Pressure (mmpatients on litters,five of whom were on ventila- tors.Two patients already had undergone leg am- putations.[T]he flights were cleared to fly directly to San Antonio and thus were able to do so in less than 2 hours 23(p1225)Military anesthesiologists need to be aware that to overcome shortfalls ofstrategic evacuation capa- bility during a major war,the air force,in conjunc- tion with a number of airlines and the U.S.Depart- ment of Transportation,has expanded the existing Civilian ReserveAir Force program to provide air- craft dedicated to aeromedical evacuation.The primary aircraft to be provided to support aero- medical airlift is the B-767.Once activated,each B- 767would be reconfigured from its civilian passen-Military Medical Evacuationger configuration to an aeromedical configuration in about 18 hours.Because casualties who enter the U.S.Air Force medical evacuation system during wartime should be medically stable,the prioritizing of precedence for picking up and moving casualties is more com- monly applicable to emergency situations such as peacetime disasters²4.·URGENT:pick up immediately·PRIORITY:pick up within 24 hours ·ROUTINE:pick up within 72 hoursThe air force places considerable importance on the classification of patients to be evacuated(Exhibit 27-6).2pF-1)The great majority of combat casualties will be placed into Classes 2A and 2B.MEDICAL IMPLICATIONS OF BIOPHYSICALEFFECTS OF AEROMEDICAL EVACUATIONMany potential problems are associated withmaintains ambient cabin altitude at a barometric pressure equivalent to that found between 1,500 and 2,600 m.Despite all the problems of living in a strange environment,“aeromedical transport of pa- tients presents no problems so long as oneremembers that man is adapted for life at sea level.&quot;25(p237)Barometric PressureBarometric pressure falls as a function of height above the surface of Earth (Figure27-14).This fact explains not only theetiology of hypoxiaat altitude空aeromedical evacuation,but most of the uniquethreats are specific to long-range flight at high alti-tude and are a consequence of human adaptationsto life at sea level.The modernjet must fly at thehighest possible levels(9,000-12,000m)for reasonsof speed,fuel economy,and comfort.At12,000 mthe barometric pressure is only 140mm Hg.At thislevel,the partial pressure of oxygen is approxi-mately30mm Hg,which cannotsustain human life.Jet aircraft can operate at such altitudes only be-cause the pressurized cabin was developed,whichFig.27-14.Barometric pressure as a function of altitude.Altitude(meters)Anesthesia and Perioperative Care ofthe Combat Casualtybut also why gastrapped withinbody cavities,as well as gas used to fill medical devices,can constitute a significant hazard to casualties undergoing aero- medical evacuation.The effect of falling barometric pressureis understandable in terms of the gaslaws of Boyle and Dalton.Boyle's law states that at a con- stant temperature,the volume of a gas is inversely proportional to the pressure towhichit is subjected. As altitude increases in an unpressurized aircraft andas barometricpressure decreases,gas ina closed or semiclosed space expands.All common drug vials,albumin infusions,and medical containers act like closed spaces when taken to altitudePatients with pneumothorax,bowel obstruction,and other conditions in which gas is trapped inaclosed spaceare at risk.The most serious problem occurs in casualties who have an untreated pneumothorax. In properly treated casualties,a chest tube attached to a one-way valve will have been inserted and left in place until the air leak has sealed.However,if undetected prior to evacuation,the volume of trapped gas will increase as the ambient pressure falls,producing a degree of cardiorespiratory em- barrassment that may require urgent decompres- sion.Therefore,incases ofsuspected pneumothorax, it is essential to obtain a chest radiograph prior to evacuation.It is much easier for the physician and safer for the patient to delay the evacuation,or,if evacuation must take place,toinsert the chest tube, before departure.The alternative is being pre- sented with the need to perform an arduous and dangerous act during the flight.Expansion of gasin the intestinal tract can also give rise to problems.Although only small vol- umes are involved,there is a theoretical risk that the expansion of the gas could produce damage to anastomotic suture lines following intestinal surgery or dehiscence of the abdominal incision. One of the earlier tenets of air evacuation was to defer moving recently operated patients for at least 14 days although,based onIsraeliexperience with aeromedicalevacuation starting with the Yom Kippur War and continuing through the Lebanon Warof 1982,recentabdominal surgery is no longer considered a contraindication if the gastroin- testinal tractis kept decompressed withanasogastric tube.26In a group of patients with paralytic ileus who were treated with hyperbaric oxygen,studies have shown that high concentrations of oxygen can re- duce abdominal distension.It is possible to move casualties who have had recent operations if the patients receive 100%oxygen(via mask or endotra- cheal tube)during the flight.27Of paramountimportanceis the status of the endo- tracheal tubeortracheostomy cuff balloon,which will expand at increasing altitude.This expansion can preclude patient ventilation and cause pressure ne- crosis of the tracheal wall.Although the volume of air used to inflate the cuff of an endotracheal tube used for ventilatory support is small,the changes in vol- ume can produce complications evenwhenusing the modern,low-pressure,high-volume cuffed endotra- cheal tube.It isessential that the cuffbe inflated with eithersalineor water to overcome this further compli- cation of a change in ambient pressure.During long-range medical evacuation,many casualties will be receiving intravenous fluids,the daily requirements of which have been carefully calculated.The fall in ambient pressure in the air- craft cabin can cause an appreciable acceleration of the rate ofinfusion because the volume of air in the intravenous infusion set will increase with increas- ing altitude.Adrip chamberwith a total volume of 9mL that contains 2 mL of fluid at sea level will be completely empty at2,000m.It is therefore essen- tial to monitor the drip rate,if infusion pumps are not in use.Care must be taken to ensure that ade- quate replacement fluid volumes are available (itis very difficult to obtainextra supplies while flying at 10,000 m).A final precaution to be observed is that all infusion fluid should be carried in flexible plas- tic containers,not in glass bottles,which could explode during the flight.The problems associated with expansion of gas in closed spaces is found in air-pressure splints including pneumatic antishock garments(PASGs) and even certain types of stretchers.As ambient pressure decreases,the transmural pressure across the wall of the PASG will increase,causing it to inflate and thereby compress the casualty's incar- cerated extremities and lowertrunk.This effect is especially noticeable above1,000m.If the trousers are inflated while in flight,the opposite effect oc- curs during descent of the aircraft:the PASG be- comes flaccid and therefore less effective than ex- pected.Careful attention must be paid to changes in altitude to avoid mishaps en route.Experiments in a decompression chamber confirmed the theo- retical consideration that there will be considerable increase in the volume ofairin the splintasambient pressure falls:measurements indicate a change in volume of almost 50%for every 1,000 ft,or about 16%per 100 m in altitude(—CABMcL,personal observation).In other words,the contained volume doubles for every 610 m increase in altitude.This finding is of importance in helicopter transfers, where air splints are used frequently.The vacuum stretcher consists of a mattress con- taining a vast number of polystyrene beads.In its softened state,it is molded around the casualty, giving support and a degree of comfort.As the air is extracted from the mattress,the beads expand so that the mattress makes a total-body splint.How- ever,as the ambient pressure falls,support de- creases,requiring the further evacuation of air to maintain the support.During the descent,the sup- port pressure increases and it is essential to main- tain close control of the mattress's rigidity.OxygenationWhile changes in air pressure are critical,given their potential for causing complications,of even greater importance is the need to deliver an ad- equate amountofoxygen not only to the patient but to the flight crew as well.The degree of hypoxia depends on the partial pressure of oxygen (Po₂)in the atmosphere.The Po₂decreases in direct pro- portion to the decrease in pressure because the concentration of atmosphericoxygen remains about 21%.Therefore,at sea level,with barometric pres- sure approximately 760mm Hg,the Po₂indry airis 169mm Hg(21%of 760mm Hg).At3,000m,where the barometric pressure is about 500 mm Hg,the partial pressure is 105 mm Hg(21%of500 mm Hg). At the summit of Mount Everest (8,848m or 29,028 ft,which is slightly below the normal cruising alti- tude of modern jet transports),the measured baro- metric pressure is 253 mm Hg and the estimated Po₂ is53 mm Hg.Owingto the presence ofwater vaporin the lungand depending on the respiratory rate,the partial pressure of alveolar oxygen (PAO₂)will be lower to avariable extent.The measured PAO₂on the summit of Mount Everestis 35 mm Hg,from which an arterial Po₂(Pao₂)of only 28 mm Hg can be calcAul<img src="/media/202408//1724832309.549043.png" /><img src="/media/202408//1724832309.5517929.png" /><img src="/media/202408//1724832309.553455.png" />dp.<img src="/media/202408//1724832309.5552871.png" /><img src="/media/202408//1724832309.5572999.png" /> consideration of the effect of baromet- ric pressure on Po₂explains why signs of hypoxia become increasingly obvious in even healthy per- sons as they fly higher than 3,000mwithoutsupple- mental oxygen.As Po₂falls,the amount ofoxygen transported byhemoglobin also falls,but thereduc- tion is not a linear function of Pao,because the shape of the oxyhemoglobin dissociation curve is sigmoidal(see Figure 25-2 in Chapter 25,Acute Respiratory Failure and Ventilatory Management). Atsea level,the PAO₂is 100mm Hg,which results in an arterial oxygen saturation of 95%.As a person goes to higher altitude,the Po₂in the surrounding air decreases,resulting in a decrease inthe amount of transported oxygen.The Po₂in blood in theMilitary Medical Evacuationlungs and arteries decreases to the point that at 3,000m,the Pao₂is about 60 mm Hg and the hemo- globin in the arteries is only about 87%saturated (Figure 27-15).Because of the sigmoid shape of the oxyhemoglobin dissociation curve,a further in- crease in altitude results in a precipitous fall in oxygen saturation,such that at an altitude corre- sponding to the summit of Mount Everest,the esti- mated arterialoxygen saturationisonly about50%— substantially below the normal oxygen saturation of <img src="/media/202408//1724832309.561724.png" /><img src="/media/202408//1724832309.563106.png" />neo<img src="/media/202408//1724832309.564537.png" />ms<img src="/media/202408//1724832309.565898.png" /><img src="/media/202408//1724832309.5674691.png" />or<img src="/media/202408//1724832309.568801.png" /><img src="/media/202408//1724832309.5702841.png" />nactes<img src="/media/202408//1724832309.571691.png" />afl<img src="/media/202408//1724832309.573189.png" /><img src="/media/202408//1724832309.5745559.png" /><img src="/media/202408//1724832309.57593.png" />le.rstanding the physics and physiology of hypoxia and oxygen delivery stems from the fact that battlefield casualties may have impaired pulmonary compliance,hypovo- lemia,anemia secondary to acute blood loss,acido- sis,and also be hypothermic—factors that impair oxygen pickup in the lungs and oxygen delivery at the cellular level.Studies carried out early in the Vietnam War heightened concern about arterial desaturation occurring during high-altitude aeromedical evacuation.It was not unusual to find casualties being prepared for aeromedical evacua- tion with an arterial Po₂of 50 mm Hg or less, breathing room air with a Po₂of 150 mm Hg.Be- cause the Po₂is about 118 mm Hg in the cabin of a C-141 pressurized to about2,400 m,a real potential existed for fatally lowarterialoxygen saturations to dev<img src="/media/202408//1724832309.578739.png" />lcocpo.<img src="/media/202408//1724832309.580148.png" />d9ingly,supplemental oxygen is needed by many casualties during aeromedical evacuation. The amount necessaryto maintain a Pao₂at 100mm Hg is shown in the upper curve in Figure 27-15.In some cases,the fraction of inspired oxygen (FIO₂) needed is so high that elective intubation with posi- tive pressure ventilation may be necessary to pre-<img src="/media/202408//1724832309.581932.png" />heannt 2s,i0g0n<img src="/media/202408//1724832309.583387.png" />a3n0t <img src="/media/202408//1724832309.584836.png" /><img src="/media/202408//1724832309.5862458.png" />aea<img src="/media/202408//1724832309.587772.png" />t<img src="/media/202408//1724832309.5890749.png" />tuhelghi<img src="/media/202408//1724832309.590486.png" />ihcea<img src="/media/202408//1724832309.591914.png" />and manpower constraints associated with the aeromedical evacuation of casualties who need mechanical ventilation,such casualties should be evacuated only in very unusual circumstances.Almost all the oxygen transported by blood is carried by the hemoglobin in red blood cells;at sea level,only 0.2mLof oxygen per 100 mL of blood is being carried in direct solution in the plasma. Therefore,the casualty's hemoglobin concentration and blood volume become important determinants of oxygen transport.Severely anemic or hypovolemic casualties are at risk during aeromedical evacuation even if their arterial oxygen saturation exceeds 90%. Hemoglobin levels should be measured prior to transfer in casualties who had sustained acute blood loss;the lowest acceptable level is approximatelyAnesthesia and Perioperative Care of the Combat Casualty<img src="/media/202408//1724832309.594888.jpeg" />Fig.27-15.Maintenance of arterial Po₂with supplemental oxygen.7.5g of hemoglobin per deciliter of blood.A level of 10 g/dL will have already set into motion the several physiological compensatory mechanisms and so the casualty will be able totolerate air trans- port.31Blood volume cannot be so easily checked but is an equally important determinant of oxygen trans- port.Astudycarriedout on casualties waiting tobe evacuated from Vietnam found that 13 of 43 were hypovolemic,and an additional 8 were hyper- volemic.Hematocrit values were notuseful indica- tors of volume status,although anemic casualties were usually hypovolemic.Hypovolemia was es- pecially common incasualties who were evacuated within 2 to 3 days of being wounded.29Gravitational and Accelerative ForcesWhilenot commonly thought of as causing pa- tient problems,the effects of gravitational forces(g) can be quite detrimental duringaeromedical evacu- ation.An individual sitting in a seat has a force equal to his weight,which is pressing against the seat.The intensity of this force,equal to the pull of gravity at the surface of Earth,is said to be 1g.The factors influencing gravitational forces are weight and its distribution;gravitational pull;and accel- eration,which is caused by the movement of the vehicle.The mostimportant effectofacceleration is on the circulatory system because blood,being mobile,can be translocated from one part of the body to another.Othertissues can also be displaced and distorted by accelerative forces,but they usu- ally remain functional.Both positive and negative gravitational forces affect casualties on medical evacuation flights.At accelerations greater than 4g,the systemicarterial pressure at the level of the heart falls to approxi- mately 40 mm Hg.Therefore,a decrease in cardiac output may occur,which is secondary to venous pooling of blood in the lower extremities.Because of this complication,patients with compromised cardiac function should be positioned with the head toward the rear of the aircraft.32The contrary process is also possible,because negative gravitational forces can cause a tremen- dous increase in arterial pressure that,when trans- mitted to the head,can cause blood pressure to rise as high as 400 mm Hg.This extreme pressure increase may cause a paradoxical effect via the baroreceptor reflex,with slowing and even stop- ping of the heart.The cerebrospinal fluid in the cranial vault may act as a buffer to the expansion of the intravascular blood volume.However,some small vessels on the surface may rupture and sub- arachnoid hemorrhages have developed inanimals exposed to negative gravitational forces.For these reasons,a casualty with a head injuryor increased intracranial pressure should be positioned with his head toward the front of the aircraft.33Thermal StressBattlefield casualties may have been exposed to the elements for extended periods.Extremes of heat and cold can both cause medical problems. The vascular system's compensatory vasoconstric- tion and vasodilation associatedwith thermalregu-lation may cause significantfluidshifts and thereby make more difficult the assessment of the adequacy of volume restoration.The volume-depleted hypo- thermic patient,whose hemodynamicsmaybefairly normal while the vascular bed is contracted,be- comes hypotensive as the vascular bed dilates inThe temperature at Earth's surface is approxi- mately 20℃;the temperature at 10,000 ft is 0℃. While mostrotor-wing flights are ataloweraltitude than10,000ft,the thermal losses toradiation,evapo- ration,conduction,and convection may be signifi- cant and underestimated.Attempts to provide at least a physiologically normal temperature will decrease oxygen consumption and improve the medical officer's ability to assess the patient.response to warmth.Noise and VibrationRotor-wing aircraft and ground ambulances create a significant amount of noise and vibration that are difficult to moderate.These factors may affect electrocardiographic monitoring,noninvas- ive blood pressure monitoring,pulse oximetry,and the auscultatory efforts of the monitoring team. Because of these limitations,the medical officer must be able to perform some form of adaptive monitoring procedure.These include palpating and assessing radial,brachial,and femoral pulses, and correlating them to mean arterial pressure; observing respiratory excursion and patterns of breathingfor any acute changesinstatus;and inter- vening appropriately.The simplicity and reliabil- ity of mechanical monitors will commonly be lost during transport.The noise levels,especially in trackedvehicles and at aircraft takeoff and landing, are a potent source of stress.Taking clinical mea- surements onunconscious patients maycause sharp risesinpulse,blood pressure,and respiration rate if protective earplugs are not used.The noise levels, especially when associated with vibrational fre- quencies above 10 Hz,are more detrimental to patient care than are the physiologicaleffects of the vibration.Military Medical EvacuationThe speed of transit can also affect the low-fre- quency vibrations to which casualties can be sub- jected.In a study of four different types of ground ambulances,marked increases intwolow-frequency areas(at 4-8 Hz and 16-28 Hz)occurred when the ambulances traveled between 30 and 45 mph.The tests were repeated in ambulances fitted with a &quot;floating&quot;stretcher.The results confirmed that the vibrations can be damped down in the specific frequency areas,but the cost of fitting this type of stretcher would be prohibitive.32Fatigue and Sleep LagThe evacuation of patients over many thousands of miles,through several time zones and different ambient temperatures,gives rise to general fatigue, due largely to disturbances of the circadianrhythms (ie,jet lag).4 In addition,even in a fit person,the longflightat reduced barometric pressure,with the resulting lowered oxygen tensions,gives rise to serious fatigue problems.The level of degradation of performance is difficult to quantify,but experi- mental work in adecompressionchamber showed a marked reduction in the appreciation and perfor- mance of tests when initially attempted,although once learned,there were no problems with reten- tion of the newly acquired skills.35 A general level of fatigue isdemonstrated by patients duringlong- distance transfer flights,especially when overnight stops are necessary.The marked improvement as a resultof directflights was firstnoted inthe German sick and wounded who were being evacuated dur- ing the Spanish Civil War:even though the aircraft were unpressurized and unheated,nonstop flights were considered better for the patients.25Workers in New Zealand have a possible treat- ment for jet lag.The pineal gland (ie,the“third” eye)secretes melatonin,which is considered to be one of the principal factors in setting the biological clock.Preliminary findings indicate that when re- search subjects take formulations of melatonin,com- pared with a placebo,the effects ofjet lag are mark- edly reduced.36MEDICAL DETERMINANTS OF SAFE EVACUATIONSpecific medical factors,such as abdominal and eye injuries,may increase the risk of medicalevacu- ation.Clearly,other factors(eg,enemy action and mechanical problems associated with the design and operation of the aircraft)may adversely affect the evacuee,but they will not be discussed here.In-Flight Medical Problems of Long-Range Aeromedical EvacuationOnly limited historical data have been gathered on the medical aspects of aeromedical evacuation. The most useful data are from the Vietnam War;Anesthesia and Perioperative Care ofthe Combat Casualtyalthough long-range casualty evacuation occurred during bothOperation Just Causein Panama(1989) and the Persian Gulf War(1990-1991),the number of American casualtieswas too small to drawmean- ingful conclusions,although much interesting an- ecdotal information was collected.The Vietnam WarThe low frequency of death observed during aeromedical evacuation(&lt;1 per 20,000 casualties evacuated)during the Vietnam War does notneces- sarily mean that nonlethal medical problems were similarly infrequent.In lieu of data from a more recent war,the U.S.Air Force medical evacuation experience in the early years of the Vietnam War, in which casualties were evacuated through an aeromedical staging facility in the Philippine Islands prior to being evacuated to Japan,is of interest.Of some 20,000 casualties already in the evacuation chain,many (68 of 128 in one check) were found to have developed signs and symp- toms indicative of the possible development of potentially serious complications.Complications were especially common in three categories of casualties29(p276)1.Vascular injuries.Of 347 casualties who had vascular reconstruction,187 were found during aeromedical evacuation to have developed signs and symptoms sug- gestive of a complication(ie,a cool, pulseless extremity;excessive pain in the limb;excessive drainage;fever).No fewer than 57 of the 187 (approximately 30%) required an extremity amputation.2.Chest injuries.Of 629 casualties who had 	chest trauma,137 were found to have a 	pneumothoraxora hemothorax.One third 	of this group,46 casualties,presentedwith 	respiratory distress,and 16 of 17 in whom 	arterial blood-gas measurements were 	made had aPao₂less than 80 mm Hg while 	breathing room air.It seems likely that 	these casualties had pathologically low ar- 	terial oxygen saturation during evacuation. 	Thirty-one casualties of the group of 137 	had a nonfunctioning chest tube in place 	Heimlich valves had been used in some 	patients and in several this was defective, 	allowing air to remain in the pleural space. 3.Abdominal injuries.Of626 casualties with 	abdominal trauma,117had signs andsymp- toms during the evacuationthat indicatedthe need for reoperation.Among the more common indications were dehiscence,evi- dence of peritonitis,intestinal obstruction, stress ulcerhemorrhage,hemorrhage from an abdominal wound,and wound sepsis.It should be understood that(a)these complica- tions were apparent after 6-hour evacuation flights, (b)many of the complications had probably existed prior to evacuation but had not been diagnosed, and (c)these casualties probably were evacuated prematurely.The Vietnamaeromedicalevacuation experience strongly suggests thatthe medical prob- lems that do develop are much more likely to be associated with the original injury than with abnor- mal environment in the evacuation.Operation Just Cause and the Persian Gulf WarThe distinguishing military medical characteris- tics of Operation Just Cause in Panama was the paucity of third-echelon medical assets deployed with the combat units.Although a surgical team was present to perform emergency lifesaving sur- gery on the critically wounded,initial surgery was performed onmost casualties inmilitary hospi- tals in San Antonio,Texas.After receiving first aid at the unit level and MASF,these casualties,to- gether with those who had already been operated on,were evacuated in C-141s,which soon became aerial emergency and intensive care wards.Not surprisingly,“In-flight care for these fresh combat casualties was a challenge for the usual crew of two flight nurses and three aeromedical evacuation technicians.&quot;37(p943)In contrast to Operation Just Cause,the Persian Gulf War was characterized by a long buildup pe- riod during which extensive third-echelon medical assets were deployed.Even so,the anticipated casualty rates were so high that the need to evacuate fresh,unstable casualties was thought to be highly likely.As a result of the Panama experience and breaking with the tradition existing since World WarII,medical commanders decided toassign phy- sicians to at least some tactical and strategic air evacuation flights so as to optimize the success of lifesaving,in-flight,medical interventions.37Fortu- nately,actual U.S.andAllied casualties were only a tiny fraction of those anticipated,and the need for lifesaving interventions was correspondinglysmall. 	The experiences in both of these wars suggest that injury-related complications,rather than the adverse physiological conditions ofthe evacuation environment,will be the major source of problems.Furthermore,it seems likely that the proportion of evacuated casualties who develop injury-related complications during evacuation will be inversely related to theintervalbetweenwounding andevacu- ation (ie,the more quickly the casualty is evacuated after wounding,the more likely it is that a compli- cation will develop).Therefore,both during mass casualty situations and when the theater evacua- tion policy is very short (eg,during a short but intense conflict),military anesthesia providers should be especially alert to the possibility of in- flight medical problems.Civilian ExperienceA relevant civilian experience also supports the view that medical problems during evacuation are more likely to be due to the original injury than due to evacuation per se.After resuscitative surgery (usually a laparotomy)was carried out in a rural hospital,patients were transferred to a regional trauma center within 48 hours of injury.No deaths occurred duringevacuation,but 8 of the 19 patients studied developed tachycardia or became hypo- tensive;7 of the 8 unstable patientssubsequently died.Transport time averaged 2.4 hours.All but 3 of the patients had blunt trauma as the mechanism of their injuries.A physician and a nurse accompa- nied all patients,all received intravenous fluids, and all but 2 were mechanically ventilated.38Patient Conditions Leading to Medical InstabilityThe major constraints placedonbattlefieldevacu- ation from and to the first and second echelons of care arise not so much from the conditions of the casualties but from enemy action and the availabil- ity of the means of evacuation.Evacuation from higher echelons may,however,be constrained by the aeromedical evacuation policy of the U.S.Air Force,which is based on the realization that some patients'medical conditions predispose to in-flight complications.The air force doesnotrecognize any absolute contraindication to aeromedical evacua- tion,but a variety of conditions either constitute relative contraindications to evacuation or require that arrangements be made for specialized treat- ment if evacuation is to proceed.2PE-3,31When theyenter theU.S.AirForce medicalevacu- ation system,casualties should be stable enough to tolerate a 1-to 24-hour trip with a high probability that complications will not occur.The necessary degree of stabilization depends on the operational situation:tacticalmissions are typically shorter thanMilitary Medical Evacuationstrategic missions.Therefore,less-stable patients might tolerate tactical evacuation,but strategic evacuation might be highly detrimental.Abdominal InjuriesPatients with abdominal injuries should be care- fully evaluatedby a general surgeon prior to flight. Use of nasogastric or rectal tubes or both should be considered to avoid both the distention frequent- ly encountered with a nonfunctioning bowel and the gas-volume changes associated with varying barometric pressure.Extra colostomy bags should accompany the patient.Drainage is more profuse at altitude because of gas expansion.It is essen- tial that military surgeons close allabdominal inci- sions with retention sutures to minimize in-flight dehiscence due to expansion of intraabdominal gas.Cardiovascular DiseasePatients with severe cardiovascular disease usu- ally have reduced tolerance to hypoxia,but they generally do well during flight ifprovided supple- mentaloxygen.Withappropriate preparation moni- toring,patients with recent myocardial infarctions can usually be moved by airlift.Unstable patients requiring in-flightcardiacmonitoring willbemoved with a medical attendant,and the referring medical treatment facility must provide an air force-ap- proved monitor.Patients who have had a myocar- dial infarction should not be evacuated for at least 10 days,and should have been free of pain for 5 days.If monitored,such patients mustbe accompa- niedby a physician.Thoracic InjuriesChest tubes should be left in place in casualties with thoracic injuries.However,each chest tube will require a Heimlich valve and an underwaters<img src="/media/202408//1724832309.639456.png" />ttrrtubes should not be airlifted until the following conditions are met:at least 24 hours have elapsed since the chest tube was removed;·normalexpiratory andlordotic chest radio- graphs have been taken at least 24 hours afterremoval of the chesttube (just prior to airlift,if possible),withaninterpretation in thepatient's medical record;andAnesthesia and Perioperative Care ofthe Combat Casualty·an occlusive dressing has been placed at the site where the chesttube was removed.Eye InjuriesPenetrating eye wounds or surgery or both can sometimes introduce air into the globe of the eye, making it susceptible to the effects of oxygen deficiency and,especially,decreased barometric pressure.Presence of gas in the posterior chamber comes as close to constituting an absolute contra- indication to high-altitude aeromedical evacuation as there is likely to be.A delay in evacuation,oran altitude restriction,is recommended for such pa- tients.Hematological ConsiderationsIdeally,patients should have a preflight hemo- globin concentration of 10g/dL or a hematocrit of 0.30.Severely traumatized patients may haveread- ings below those levels,and supplemental oxygen may berequired.Hemoglobin concentration canbe as low as 8.5 g/dL if the patient's condition is chronic,stable,and not due tobleeding.Infectious DiseasePatients in the infectious stage of a serious com- municable disease need to be segregated from the other evacuees.Maxillofacial InjuriesDue to the increased potential for nausea and vomiting,patients with wired,immobilized upper and lower jaws must have a quick-release mecha- nism applied or have easy access to wire cutters in their possession.Premedication with an antiemetic should be considered.Neurological InjuriesThe decreased Po₂ataltitude can causeincreased intracranial pressure in casualties with head inju- ries.Low-flow oxygen and an altitude restriction should be considered for flight.Noise,vibration, and thermal stresses can precipitate seizures,and adequate antiseizure medication levels should be established before flight.Valsalva's maneuver should be avoidedby patients at risk from increas- ed intracranial pressure.Therefore,administrating a preflight decongestant and inserting a polyethyl-ene tube into the patient's middle ears should be considered,especially if the patient is comatose. Patients who have had a craniotomy should not be evacuated for at least 48 hours after surgery,and should be awake and alert.The subtle changes in neurologicalstatus that areusually discovered dur- ing routine neurological checks are very difficult to detectduring flight;patients requiring close obser- vation are poor candidates for aeromedical evacua- tion.Stable,comatose patients can be transported. Decreased humidity at altitude dictates that pa- tients withaloss of corneal blink reflex be provided with bilateral eye patches and eye ointment or liq- uid tears.Intraventricular monitoring cannot be accomplished during flight.Orthopedic InjuriesIdeally,casts on recent fractures should be at least 48 hours old.All casts should be bivalved unless that would jeopardize the stability of the fracture.Free-swinging weights for traction are unacceptable for flight.Cervical traction is avail- able via a Collins traction device;however,a medi- cal officer must be present when the device is ap- plied.Patients using crutches should travel by litter because of the safety factors involved in moving abouton unstable aircraft.Crutches should accom- pany the patient and bestowed aboard the aircraft.Thermal InjuriesIngeneral,casualties with thermalinjuries should not be evacuated during the period of fluid seques- tration (ie,the first48 h).Thermal injuries should be covered withocclusive dressings.Escharotomies are required forfull-thickness circumferential burns. Extra burn dressings for in-flight reinforcement should be provided.Limited infusion pumps and poorin-flightrefrigeration capabilities preclude the use of total parenteral nutrition.Infusions of 10% dextroseinwater with necessary electrolytesshould be ordered as ashort-term substitute.Phosphorous injuries shouldbecovered with saline-soaked dress- ings.Largevesicles and bullae should be protected during the evacuation with large,bulkydressings.Vascular InjuriesVascular repairs should be clearly recorded on Patient Evacuation Form DD602 or 1380.Casts that are less than 48 hours old should be bivalved and windowed over the injured area in case excessive swelling occurs during flight.Psychiatric IllnessSeverely ill psychiatric patients(Classification 1A)require a litter,leather wrist and ankle re- straints,and sedation.Patients whose psychiatric illnesses are of intermediate severity (Classifica- tion 1B)require a litter and sedation,and restraints must be available.All psychiatric patients on litters must be searched,and all sharp objects such as razor blades and pocketknives must be removed as part of the antihijacking procedure.A secondary search must be accomplishedjust beforeenplaning.Drug and Alcohol AbuseSoldiers who are being treated for drugand alco- hol abuse should undergo 3 to5 days of detoxifica- tion before they areairlifted.Anaeromedicalevacu- ation mission is not equipped to deal with acute withdrawal symptoms.Preparation for EvacuationInitial AssessmentThe Advanced Trauma Life Support(ATLS) courseof the AmericanCollege ofSurgeons is taught to military physicians as part of the Combat Casu- alty Care Course.39 Prior to evacuation,the initial assessment of the casualty's condition is based on the ATLS ABCs(airway,breathing,and circulation) and the extent and location of injury,especially when the time available for battlefield medical implementation of ATLS is short and injuries may have been missed.The“Golden Hour”concept,which arises from the civilian trauma experience,suggests that if a trauma patient with a survivable injury who is in clinical shock does not receive the definitive care necessary to reverse the process within the first hour after entering the shock state,the long-term survivability drops below 10%.Thisis independent of the quality of care after that 60-minute period.30 In the context of combat casualty care,providing care within the Golden Hour is important,because about 90%of the total combat mortality occurs within the first hour after wounding(see Chapter1, Combat Trauma Overview,for a more complete discussion).In Vietnam,transport took35 minutes after the patient was loaded.40 The Germans⁴¹and Swiss²can transport at least 90%of their popula- tion in 15 minutes or less,but of course conditions for civilian aeromedical evacuation in these coun- tries are more favorablethan they were in Vietnam:Military Medical Evacuationthere is no need to pickup casualties from a dense jungle or from a landing zone exposed to enemy small-arms fire.The chaos of the battlefield or aid station may preclude an organized approach to each casualty. However,the rules of assessment,resuscitation, and stabilization must be followed in an orderly manner.This provides as safe a mechanism as possible for the transport of the trauma patient.Supplies and Equipment Required From the Originating Medical Treatment FacilityThe MASF does not have any equipment that can be given in replacement:all equipment and sup- plies that eachcasualty will need during the entire evacuation process must be supplied by the origi- nating medical treatment facility(MTF)and accom- pany the casualty to the aeromedical staging facil- ity.U.S.Army anesthesiologists should be aware of the following U.S.Air Force requirements for sup- plies and equipment³1:·Patient medications.Patients transported intratheater should be given a 3-day supply of medications and supplies;intertheater patients should be given a 5-day supply. Intravenous fluids.The referring MTF should provide a 3-day supply of intrave- nous fluids and infusion equipment,in- cluding all necessary supplies for antibi- otic administration,if required.● Special medical equipment.Special equip- ment includes cardiac monitors,ventilators, Stryker frames,continuous-suctionunits,pulse oximeters,oxygen analyzers,and restraints.As a rule,dressings will be reinforced but not changed during flight due to the relatively unclean in-flight environment.Serious complications such as bleeding,increased pain,or swelling may re- quire wound inspection.Routine dressings willbe provided by the air evacuation crew;however, unique dressings or dressings for patients with excessively draining wounds should be provided by the originating MTF.Physician's OrdersAlthough the recommendation has been made that flight surgeons augment the basic air evacua- tion crew on selected tactical and strategic evacua- tion missions,37 the absence of physicians on most U.S.Air Force aeromedical evacuation missionsAnesthesia and Perioperative Care ofthe Combat Casualtyemphasizes the absolute criticality that clear and concise orders,covering the entire patient transfer, be written on the Patient Evacuation Tag,DDForm 602.The referring physician is legally responsible for all medical care until the patient reaches the destination facilityStretchers and Securing the Casualty in the AircraftThe first principle of aeromedical evacuation is that the casualty must be securely fastened to the evacuation platform.If a casualty has an extremity fracture,the fracture must be immobilized for both safe and humane transportation.This is especially necessary when bumpy ground evacuation is ex- pected.Atthis time,there are atleast 30 differenttypesof stretchers available for use by NATO forces,con- structed from various materials,but still based on the Swiss designs of 1912 and 1922.This multiplic- ity of stretchers can lead to problems in locating the stretcher in the different types of transport.With the wealth of new materials available at the end of the20th century,itseems remarkable that a suitable stretcher hasnot been developed thatis compatible with the road,rail,sea,and air requirements.In a mass casualty situation,the loading of stretcher patients is important:more seriously ill casualties must be positioned to ensure all-around access for the medical and nursing team.Also,adequate fa- cilities must be availableat the departure airhead to enable rapid loading of the casualties.It is also necessary tohave the ground facilities to maintain full medical care for at least 24hours,should there be a delay in the evacuating flights.The differing aircraft likely to beused have load- ing doors at varying heights above ground.Some, like the C-130 Hercules and the C-141 Starlifter,can of course be loaded directly,but when commercial jets such as the VC-10,Lockheed 1001,and Boeing 737,747,and 767 are used in medical evacuation, special loading ramps are necessary.In all forms of transportation,but especially by air,it is essential to ensure that the patients are securely strapped to their stretchers,.These,in turn,are located on the fixed stretcher supports to minimize the acceleration and deceleration forces that are generated during ground transportation and takeoff and landing of fixed-wing aircraft.Stretchers are traditionally placed longitudinally, with the casualty traveling head first,whatever form of transport is being employed.Many have suggested that the ideal siting of stretchers wouldbe transverse:across the aircraft cabin.This siting would lessen the fore-and-aft movements of body fluids during the acceleration and deceleration phases of travel.Stryker frames are generally indicated for paraplegia,quadriplegia,cervical fractures,severe burns,and those patientsrequiring total assistance. Patients with cervical injuries and wearing halo traction may be transported on a regular litter or,if stabilized,they may be transported as ambulatory patients.All components of the Stryker frame must be sent with the casualty from the originating MTF to allow continuity of patient care and turning of patients throughout transfer.Stretcher frames and the stretcher harness must be stressed to atleast 6g to give a wide margin of safety should it be neces- sary toabandon the takeoff in a fixed-wing aircraft.CathetersIntravenous Infusions.The military anesthesi-ologist must be extremely attentive to the establish- ment,securing,and maintenance of intravenous lines.These lines are important for the continued resuscitation of the casualty as well as for the ad- ministration of needed pain medication and other drugs.The establishmentoflarge,easilyaccessible, secure lines should be uppermost in the anesthes- iologist's mind,as these lines may provide the only means of drug delivery.Patients who require intravenous fluids on the ground will also require them during the flight, owing to the excessively dry cabin environment. Catheter function should be assessed prior to trans- port to ensure that the catheter is securely in place. Patients requiring antibiotics without fluid replace- ments should be switched to a heparin lock with heparin flushes provided.A 3-day supply of intra- venous fluid should accompany each patient who requires intravenous fluids.Urinary Catheters.Indwelling urinary catheters and drainage bags in use beforetransport shouldbe left in place during evacuation,or inserted before the flight if urinary retention is a problem.The internal balloon should be filled with sterile,nor- mal saline or water instead of air to avoid gas expansion during the flight.Nasogastric Tubes.Nasogastric tubeinsertion is recommended for patients withabdominal wounds, abscesses or obstructions,paraplegia or quadriple- gia,or the potential for paralytic ileus.Limited suction capabilities are available aboard the air- craft;however,the distalend of the tube may beleft to drain by gravity into a glove or bag.Respiratory SupportThe utmost concern in the mind of every anes- thesiologist isthe adequacy of the patient's airway and therefore of the patient's ventilation.The need toestablish a definitive airway rapidly is foremost in ATLSinstruction.Several aspects of the mainte- nance of apatentairway during aeromedical evacu- ation deserve special mention.AirwayManagement.Endotrachealtubesshouldbe used if the patient requires assisted ventilation and should beinserted before aeromedical evacua- tion begins.Balloon cuffs should be filled with normal saline instead of air,as gas expansion at altitude may cause tracheal damage.Airway Stability.Several questions must be answered while the casualty is being prepared for evacuation.Is the patientbreathing spontaneously? Will the patient's airway need attention?What is the potential that the patient's airway will be com- promised?The significance of the airway in air ambulance transport revolves around the ability to control ventilation and the need for personnel (nurses,medics,respiratory technicians)and equip- ment to aid that ventilation.Coexisting injuries may compromise the airway,such as cervicalinsta- bility and severe facial trauma including LeFort fractures.The military anesthesiologist must re- member that airway problems are especially com- mon in casualties with burn injuries.Tracheostomies.Tracheotomy tubes should be changed before flight and an extra tube should be sent with the patient.Ventilators.Ventilator-dependent patients willbe accompanied by a respiratory therapist or otherappropriate medical attendant from the referringMTF.The apneic patient requires full ventilatorysupport from a respirator that will provide auto-maticcontrol.There are many suchmachinesavail-able,but in the context of military aeromedicalevacuation,it is likely that compactness and dura-bilitywill be preferred to sophistication (ie,a mul-titude of dials and controls,such as those seen inintensive care units).A further constraint is themode of operation.All but the simplest ventilatorsrequire a compressor to provide the gas that drivesthe ventilator.Transportation ventilators must belightweight,rugged,durable,and simple to oper-ate.Manual ventilation may be all thatis availableon a helicopter flight.Humidifiers.Because the ambient cabin humid- ity during long-distance aeromedical evacuation is usually between 5%and 20%,marked insensible water loss anddrying of therespiratory tractshouldMilitary Medical Evacuationbe expected.This consideration applies to all pa- tients but especially to those in whom the normal humidifying functionof the noseis prevented,such as casualties with a tracheostomy or an endotra- cheal tube.It will therefore benecessary toprovide adequate humidification to avoid the problems of ventilating with dry gases.There are many humidifiers,as there are ventila- tors,but the simplest,and therefore the mostappro- priate,device is the small condenser humidifier, which can be plugged into theventilating circuit.A lightweight item,it works by passing the fresh gases through the condenser foilon which the water vapor in the expired air condenses.The water is then available to humidify the inspired oxygen.A bonus,of course,is the degree of heat conservation achieved during the respiratory cycle.The effi- ciency of the&quot;Swedish nose&quot;(the Humid-VentHeat- MoistureExchanger,manufactured by Gibeck Res- piration Co.,Uplands,Väsby,Sweden)is such that a relative humidity of approximately 50%can be maintained during the transfer.43Oxygen.There are many simple devices avail- able todeliver oxygen,ranging from nasal cannulae and the simple mask,which deliver variable con- centrations and flows of oxygen,to fixed-dilution Venturimasks,whichare capable of delivering24% to 50%oxygen.It is difficult to tap into the main aircraftoxygen supplies,so thesourceofoxygenfor patients mustbe cylinders;however,when required in large numbers,oxygen cylinders produce a se- vere weightpenalty.Afurther problem is the avail- abilityof adequate numbers of theappropriate cyl- inder sizes.It is therefore necessary to consider alternative sources of oxygen for in-flight use.Liquid oxygen,despite being considered insome quarters to be dangerous cargo on aircraft,offers an excellent alternative means,as canbe seen from the volumes of gaseous oxygen available from one 30- Lflask ofliquid oxygen:one suchflaskis equivalent to 18 large cylinders of compressed gas,with the obvious weight savings.The problem of fitting a heat exchanger to avoid freezing of the delivery outlet can be overcome without much difficulty. The pressure-swing absorbersystem(ie,theoxygen concentrator)mustalso be considered as a source of additional oxygen.The concentrator works by forc- ing dried ambient air,at a low pressure,through fractionating columns of zeolite crystals.As air passes through the zeolite,all other constituents of air are removed except oxygen and argon.At the delivery end of the unit,a mixture of up to 95% oxygen and 5%argon is obtained,at a rate of 4L/ min.Of course,thisis notthestandard required forAnesthesia and Perioperative Care ofthe Combat Casualtymedical oxygen,but is a perfectly satisfactory oxy- gen supply.There have been no reports of the effects of ventilatingwith a mixture of oxygen and argon.The oxygen concentrator requires a power source to drive the compressor and produce a con- tinuous supply ofoxygen,but little maintenance.If the flow through the columns is increased,ahigher volume of oxygen is produced,but the percentage of oxygen falls in direct relation to the increased flow through the columns.Fracture StabilizationThe problems that increasing and decreasing gravitational forces exert on fractures during air- craft acceleration and deceleration have already been discussed.It is during the transport of pa- tients with severe fractures that the problems as- sume great importance.Most patients transported by air or ground am- bulance will be immobilized on stretchers or gurneys.The ability to maintain in-line traction for cervical injuries as well as continued support for long-bone fractures is essential.The goal is to preventthe conversion of stableinjuries to unstable injuries.It is necessary in all cases of spinal frac- ture,especially the cervical spine,with or without paralysis,to ensure that the degree of traction on the spine is maintained accurately.Although mod- ern jets will be flying above the weather,there is still the problem of clear-air turbulence.When this happens,the gravitational forces exerted as the air- craft is bounced about can increase 4-to 5-fold,so that a traction weight of 101b will immediately increase to 40 or 501b,with the obvious deleterious effects on the patient,eventhough such forces occur for extremely short periods of time.The Stryker frame or its derivatives used for transferring patients with spinal fractures did not address the problemsof(a)rapid increasesin forces exerted and(b)difficulty in moving the frame and patient.4 The Povey turningframe addressesmany ofthe problems experienced with the Stryker frame.45 It weighs only 701b and can easily be moved.The traction weights are maintainedhorizontally,elimi- nating the high vertical-acceleration forces.The weights can also be maintained during any neces- sary nursing procedure.The Povey frame takes up much less space on the aircraft,and the amount of whip during turbulent conditions is much reduced.The whole frame can be turned through 360° while head and neck traction are maintained.Thisis important for the nursing care of patients with fracture and paralysis.In the quadriplegic patient, it is essential to maintain full nursing care to the skin,which,deprived of sensory input,can rapidly become broken and developserious infection at thedamaged area.Historically,motion sickness does not appear to have been a significant problem in transporting physiologically stable casualties.In all cases of spinalinjuryitisessentialto ensure thatanasogastric tube is passed prior to takeoff,as one of the imme- diate and fatal complications of such injuries is acute dilation of the stomach,leading to massive emesis.The presence of the tube will permit con- tinuous aspiration of the stomach,thus avoiding the complicationCasualty Assessment and MonitoringIdeally,the same monitoring equipment found inanintensive care unitinafourth-echelonhospital (or a Level-1 trauma hospital)would be available throughout the evacuation chain.Obviously,how- ever,logistical realities constrain equipment avail- ability.Inspection of the patientis probably still the best monitoravailable.As with the ventilators,it is necessary thatall items used must be rugged,light- weight,and compatible with the aircraft type.The power supplies in aircraft vary so,as the degree of sophistication of the electronic monitors used in- creases,it is necessary to know the type of airplane to be used.All monitoring equipment generates a degree of electromagnetic interference,which can interfere with navigational or communication equipment of theaircraft.Itis therefore necessary forallmonitors to be tested for such interference.Standards have been formulated,but at this time very few of the items tested havereceived a seal of approvalonfirst testing.46It would seem logical to employ battery-oper- ated monitoring equipment in an attempt to avoid electromagnetic induction.There are,however, problems with the type of battery available during air transport.The sight of an acid-filled battery being carried aboard—even thenonspill type—will raise concerns aboutsafety.The duration of battery life is alsoan important considerationasthe battery chargers available for use give rise to an induction field,which precludes their used in flight.Several monitoring packages are now being produced that will,it is hoped,satisfy the safety requirements.Military Medical EvacuationSUMMARYThe requirement to evacuate the sick and wounded is of much greater importance in military medicine than it is in civilianmedical practice.This fact is a consequence of one of the distinguish- ing characteristics of military medicine:the provi- sion of care by echelons.The nature of evacuation and the conditions under which it is carried out differ according to the echelons.At one extreme is the army's evacuation from the battlefield of gravely wounded,unstable combat casualties by ground ambulance or rotor-wing aircraft.At the other extreme is the air force's intertheater(strate-gic)evacuation of stable combat casualtiesby long- range jet transport.The medical complications of evacuation arise primarily from the basic injury,but aspects of the somewhat unphysiological en- vironment of high-altitude,long-range aeromedi- cal evacuation may contribute to morbidity and even mortality.Foremost among these are(a)de- creased barometric pressure,which can cause ex- pansion of abnormal collections of gas trapped within thebody;and(b)decreased Po₂,which may give rise to arterial desaturation and defectiveoxy- gen transport.It is imperative that military anes- thesiologists understand how to order and to carry out evacuation from the battlefield and from the levels of care in which they ordinarily practice. 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