coNCEPTS, COMPONENTS, AND CONFIGURATIONS

Some Considerations Before Using the Aerial Ambulance

Benjamin Welch, MD Louisville, Kentucky

The use o f aerial ambulances for mov ing patients to hospitals requires some special clinical considerations. Various altitudes produce clinical problems. The Federal Aviat ion Agency has requirements for equip- ment. Factors to be cons idered in selecting the m o d e of transporting an emergency patient include patient's condition, weather, and landing lo- cation at destination. There are l imitations as wel l as the advantages in using aerial ambulances .

Welch B: Some considerations before using the aerial ambulance. JACEP 6:155-157, Apr=l, 1977, a~rborne medical care umts, patient transfer.

INTRODUCTION

After 106 years of manned flight, there are ae r i a l ambulance sys tems (AAS) evolving t ha t will de l iver pa- tients to hea l t h care faci l i t ies quickly and direct ly wi thout i n t e r rup t ing life support. 1 These AAS can also t rans- port med ica l suppl ies , blood, blood components, and o rgans for t r a n s - plantation; t r anspor t consul tan ts to hospitals; t r anspor t medical person- nel to accident and d i sas te r scenes; provide mass evacuat ion of the sick and i n j u r e d , and e x t e n d the geo- g raph ic a r e a s of e f f e c t i v e n e s s of major medical centers. 2-5

Fur the r developments are needed

From the Department of Emergency Med- Icine, Louisville General Hospital, Louis- ville, Kentucky.

Presented at the Kentucky Chapter of the American College of Emergency Physi- cians program at the Kentucky Medical Association Annual Conference in Sep- tember, 1975.

Address for reprints. Benjamin Welch, MD, PO Box 99517, Jeffersontown, Ken- tucky 40299.

in a i r c r a f t i n t e r c o m m u n i c a t i o n s , a i r - t o - g r o u n d r e l a ys , e f f i c i en t en- g ines to r e d u c e fuel e x p e n d i t u r e , s i m p l i f i e d m a c h i n e s to r e d u c e m a i n t e n a n c e costs, and h e l i c o p t e r v i b r a t i o n r e d u c t i o n . D e m a n d s for s t anda rds in f l ight equipment , medi-

, cal f l ight personnel competence, and p a t i e n t s e l e c t i o n c r i t e r i a wi l l , no doubt, continue.

FAA MINIMUMS

The Fede ra l Avia t ion Admin i s t r a - t ion (FAA) has set some m i n i m u m equ ipment r equ i rements for a i r am- b u l a n c e s (Table 1). 6 Added equip- men t requ i res considerat ion of these f ac to r s : w e i g h t , d u r a b i l i t y , s ize , s h a p e , p o r t a b i l i t y , s a f e ty , a d a p t - ab i l i ty to a i rcraf t , ab i l i ty to use air- craft power outlets , and expense.

RESPONSIBILITIES

As in g r o u n d ~ m b u l a n c e ope ra - tions, those who choose to use AAS fo~ i n t e r h o s p i t a l t r a n s f e r r a l s m u s t r e c o g n i z e t h e i r o b l i g a t i o n s . The t r ans f e r r i ng pa r ty is probably lega l ly responsible for the pa t i en t un t i l he

e n t e r s t h e doors of the r e c e ~ v m g facil i ty. This responsibi l i ty includes a r r a n g i n g the t ransfer wi th the re- ce iving hosp i ta l before sending the pa t i en t and providing adequate pa- t i en t care dur ing t ranspor t . 7

The pilot is in complete command of the a i r ambulance though he con- s iders the medica l a t t e n d a n t ' s rec- o m m e n d a t i o n s c o n c e r n i n g p a t i e n t welfare and s tatus . Safety of the ve- hicle crew and passengers is foremost in al l ambu lance miss ions whe the r t h e y a r e r o a d s i d e p i c k u p s or in- t e rhosp i t a l t ransfers .

GENERAL CONSIDERATIONS

Severa l factors may de te rmine the selection of pa t i en t t r ans fe r method. For example , a mobile ground coro- na ry care uni t is probably be t te r for t r a n s p o r t i n g pa t i en t s w i th myocar- d ia l infarct ions than an aer ia l ambu- lance in t u rbu len t weather , par t icu- l a r ly when the distance is short. Ex- t e rna l s t ress produces increased car- diac i r r i t a b i l i t y and a r rhy thmias , s

If the a i rc ra f t wil l not ]and direct ly at t he r e c e i v i n g hosp i t a l , the t r ip from a n e a r b y a i rpor t m a y fu r the r e n d a n g e r t h e p a t i e n t w i t h e x t r a j o s t l i n g ( d a n g e r o u s in s p i n a l in- juries) . Also, the t ime gained by fly- ing could be lost by the t ime t aken for the ground ambulance t ransfer .

The a t t e n d a n t access to the pa t i en t should be easy and unobstructed. I t is difficult, if not impossible, to rear- range a pa t i en t in most a i rc ra f t in

~ ] ~ P 6:4 (Apr) 1977 155/41

Table 1 FAA REQUIREMENTS*

fl ight. The to ta l work ing space in one of t he common, l a r g e r he l i cop te r s used today is 8' x 4.4' x 3.3', less than s t andards set for ground ambulanc- es. 9 F ixed wing a i rcraf t accommoda- t ions vary considerably.

Next, one mus t ask if the a i r vehi- cle can be approached and en t e r ed safely. People have been ki l led or se- r i o u s l y i n j u r e d w h e n s t r u c k w i t h b lades and propel lers . The ma in ro- t a ry wing of hel icopters can dip. The added s lan t to the machine when it is r es t ing on a slope wil l br ing the blade closer to t he ground. W h i r l i n g ta i l rotors are nea r ly impossible to see in s u b d u e d l i g h t , F l y i n g d e b r i s can cause corneal abras ions . Noise is lit- e ra l ly deafen ing wi th chronic expo- sure. Hea r ing protect ion for al l per- sons on board l i gh t a i r c ra f t is ad- vised, lo

ALTITUDE AND OXYGENATION

S i m u l a t e d a l t i t u d e s ins ide pres- surized cabins of commercia l Ameri - can car r ie rs vary. For instance, a t an ambien t 40,000 ft a l t i tude the inside cab in p r e s s u r e of a Boeing 707 is 7,500 feet, while a t 22,500 feet the inside cabin a l t i tude is a t sea level. 11 S m a l l e r , u n p r e s s u r i z e d craf t com- m o n l y f ly a t 10 ,000 feet . L a r g e hel icopters can eas i ly fly at 10,000 ft. Mounta ins or bad wea the r can a l te r a f l ight pa th and create the potent ia l for hypoxia in a normal person.

Shi l l i to 12 exposed pu lmona ry pa- t i en t s to s i m u l a t e d a l t i t udes up to 8,000 feet. Those wi th sea level arte- r i a l o x y g e n s a t u r a t i o n s less t h a n 90% t o l e r a t e d the a l t i t u d e poorly. F u r t h e r m o r e , in those cases where the m a x i m u m vo lun ta ry vent i la t ion was 40 l i t e r /min or less, there was poor to lerance to a l t i tude . He noted tha t the ab i l i ty to hype rven t i l a t e is essen t ia l if a person is to to lera te ex- posure to a l t i tude ,

Henry et al ~3 s tudied the effects of hypoxia on t r auma t i zed pa t ien ts and produced a n o m o g r a m from which p r e f l i g h t a r t e r i a l o x y g e n t e n s i o n s can be used to p r e d i c t i n f l i g h t hypoxemia.

M a r g i n a l o x y g e n a t i o n of t i s sues from w h a t e v e r cause (eg, anemia , blood loss, impa i red pu lmonary func- tion, or the inab i l i ty of the body tis- sues to use oxygen) may be a cr i t ical factor a t a l t i tude .

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1. Must have space for attendant to be seated at patient's head. 2. Must have sufficient space for attendant to have access to patient. 3. Approved litter tie-down and patient restraints. 4. Method of securing intravenous solutions during flight. 5. Resuscitator compatible with aircraft system. 6. Suction apparatus (foot-pump operated is not adequate). 7. Sufficient therapeutic 02 to meet patient's needs for the duration of

the flight. 8. Humidification equipment. 9. Sheets, blankets, pillows.

10. Disposable urinals, bed pans, emesis basins. 11. Provisions for ace and oral liquids. 12. Medical attendant's kit

a) sphygmomanometer b) stethoscope c) otoscope d) thermometers (oral, rectal) e) nasal spray (vasoconstric-

to r)

f) airway g) antimotion sickness drug h) aspirin i) tongue depressors j) prepackaged moistened

towelettes

*From Department of Transportation 6

Table 2 ALTITUDE LIMITS FOR PATIENTS WITH CARDIORESPIRATORY

DISEASES (WITHOUT SUPPLEMENTAL 02)*

Limit (feet)

10,000

8,000

6,000

Problem

Any suspected or symptomatic cardlores- piratory disease

More than mildly symptomatic Marked ventilatory restrichon

Recent MI (8 - 24 weeks) Angina pectoris S,ckle cell d,sease Alveolar block with cyanosls

/ C l i n i c a l cyanos i s

any one ~ C o r ;rulmonale

~Respir rato ry acidosis

4,000 Severe card,ac disease with cyanosls or recent decompensation

Patients with any two: chnical cyanosis or cur pulmonale or respiratory acidosis

2,000 Card,ac patients an failure MI 8 weeks Patients with all three:

clinical cyanosis cur pulmonale respl ratory acidosis

*From American College of Chest Physictans 13

Persons af fec ted w i th s ickle cel l d isease are suscept ib le to m a r g i n a l oxygenat ion of t issues. Painful crises have affl icted b lacks wi th sickle cell

disease and t r a i t dur ing low alt i tude f l ights and in chambers at s imulated heights of 4,000 to 6,000 feet. 1~ For these reasons, if a pa t ien t ' s hemoglo-

6:4 (Apr)1977 ~ P

bin is less t han 8.5 gm/100 ml, or r e d blood cell counts are equal to, or less than, 3 ,000,000/cu mm, o x y g e n should be administered during flight, n The re t ina has the highest oxygen demand of any organ m the body} 6 Above 10,000 ft, hypoxia produces di- latwn of the r e t i na l and choroidal vessels. It is very possible tha t an in- dividual who has had an in t raocular hemorrhage will have a recurrence2 s oxygen should be adminis tered in- fhght to pat ients with eye injuries or postoperative eye p a t i e n t s . Cer- tainly, where there is any suspicion of a marg ina l t issue oxygen state, oxygen a d m i n i s t r a t i o n shou ld be considered dur ing flight at any al-

titude.

The A m e r i c a n College of Ches t Physicians has r e c o m m e n d e d al- titude l imi ts above which pa t i en t s with c a r d i o r e s p i r a t o r y d i s e a s e s should not be t ransported (Table 2). 14

ALTITUDE AND PRESSURE

Another area of medical concern is that of a i r v o l u m e e x p a n s i o n as- sociated with gains in alti tude. One hter of dry gas at constant tempera- ture at sea level will approximately double its volume at 18,000 feet} 5 Even moderate gas expansion could cause p e r f o r a t i o n , or p r e c i p i t a t e bleeding, of a d iseased or i n j u r e d wscus} ~ Expansion of gas located in the p l eu ra l space wil l be s l i gh t l y greater t h a n t h a t p red ic t ed by Boyle's law for dry gases because of the gas's moisture content2 s This gas expansion e m p h a s i z e s the impor- tance of placing thoracostomy tubes in pa t i en t s wi th i n t r a p l e u r a l air . Heimlich f lut ter valves 17 are simple, inexpensive, safe devices to incorpo- rate in chest tubes to allow the re- lease of expanded gas wi thou t the need for bulky, heavy water bottles.

Intra t racheal cuffs may lose their seal or become excessively snug, de- pending on al t i tude changes. Stoner and Cooke'slS data indicate tha t the McGinnis cuff with attached balloon does not exceed the tolerable l imits of t ightness agains t the t rachea at altitudes of 8,000 to 35,000 feet.

I n t r a v e n o u s s e tups shou ld be

watched closely. Excessive flow rates can become a problem when aircraft is d e s c e n d i n g . C o n s t a n t i n f u s i o n pumps are ideal to use if available. Plastic conta iners are preferable to glass because they do not shatter. If glass i n t r avenous bottles are used, they should be taped c i rcumferen- t ial ly to prevent spreading of glass p a r t i c l e s in the e v e n t the bo t t l e breaks.

VESTIBULAR RESPONSE

At h igh a l t i t u d e s where f l i gh t paths are re la t ively smooth, motion sickness is usual ly not a problem. At lower a l t i tudes in tu rbu len t air, mo- t ion sickness is more likely to occur. The v o m i t i n g p roduced can be dangerous for pa t i en t s who are in coma or who have sustained signifi- cant t rauma. That sick and injured people are more susceptible to mo- t ion sickness t han normal individu- als is not proven; this subject needs future laboratory and clinical clarifi- cation. As a general rule, pa t ien ts should not fly for ten days following major surgery. 19 Pat ients with high risk of aspirat ion should have empty stomachs before flying if at all possi- ble. Dur ing emergency flights, it is Imperative tha t suction apparatus be p rope r ly f u n c t i o n i n g . The use of ant iemetics may be considered when prepar ing pa t ients for interhospi ta t transfers. The most effective motion s i cknes s p r e v e n t a t i v e is 1.2 mg scopolamine with 20 mg d-amphet- amine. 2° Mandibu la r fractures wired so that the mouth cannot be rapidly opened are e spec i a l l y d a n g e r o u s should mot ion s ickness wi th vom- i t i n g occur. A qu ick re lease ora l brace has been designed for infl ight u s e . 19

The author acknowledges the assistance and encouragement of Donald M. Thom- as, MD, Chief, Department of Emergency Medicine, Lomsville General Hospital.

REFERENCES

1. Gibbons HL, Fromhagen C: Aeromedi- cal transportation and general aviation. Aerospace Med 42:773-779, 1971.

2. Cowley RA, Hudson F, Scanlau E, et al: An economical and proved hehcopter program for transporting the emergency

critically ill and injured patmnt in Mary- land. J Trauma13"1029-1038, 1973.

3. Jessen K, Hagelsten JO: S-61 helicop- ter as a mobile intenswe care unit. Aero- space ivied 45:1071-1074, 1974.

4. Shepard FM: Emergency transporta- tion of the neonate. Nebr Med J (pt 2):200-203, 1974.

5. Neel S: Army aeromedlcal evacuation procedures in Vietnam JAMA 204:309- 313, 1975.

6. Medical informatmn for a~r ambulance operators, Advisory Circular Department of Transportation, Federal Aviation Ad- ministration, AC No: 67-1: 6-7, 1974.

7. Abbuhl RW: Query and comment J Legal Med 5:8E, 8H, 1977.

8. Moylan JA: Civilian aeromedlcal transportation, medical indmations and contraindications. J Kan Med Soc 75:345- 352,1974.

9. Federal Specification, Ambulance Emergency medical care vehicle, ap- proved by the Commissioner, Federal Supply Service, General Services Admm- istration. KKK-A-1822: 1-39, Jan 2, 1974.

10. Moffitt OP, Lett JE, Tonndorf J: Aw- ation Otolaryngology SAM textbook No 4, Randolf Air Force Base, Texas, 1956, pp 78-84.

11. Committee on Medmal Criteria of the Aerospace Medmal Assocmtlon: Medical cmteria for passenger flying. Arch Envz- ron Health 2:124-138, 1961.

12. Shlllito FH, Tomashefski JF, Ashe WF: The exposure of ambulatory patients to moderate altitudes. Aerospace Med 34:850-857, 1963

13 Henry JN, Krems LJ, Cutting RT. Hypoxemia during aeromedical evacua- tion Surg Gynecol Obstet 136:49-53, 1973.

14. Section on Aviation Medicine, Com- mittee on Physmlog~c Therapy of the American College of Chest Physicians Air travel in cardloresplratory disease. D~s Chest 37: 579-588, 1960

15. Guyton AC Textbook o f Medical Physiology, ed 3, Philadelphia, W B Saun- ders Company, 1966, p 621.

16. Army Flight Surgeons Manual, Spe- ctal Text. ST1-105-8, Vol 2 30-55, 1970

17. Heimhch HJ: Heimhch flutter valve effective replacement for drainage bottle Hospital Topics 43: 122-123, 1965.

18. Stoner DL, Cooke JP: Intratracheal cuffs and aeromedical evacuation Anes- thesmlogy 41:302-306, 1974.

19. Harrison's Principles of Internal Med- wine, ed 6. The Blaklston Co, 1970, p 713

20. Wood CD, Graybiel A Evaluatmn of sixteen antimotion sickness drugs under controlled laboratory conditions. Aero- space Med 39:1341-44, 1968

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