Aeromedical Transportation

1. Aeromedical Transportation Sarah McPherson & Dr. A Abbi November 1, 2001

2. Outline • History • Aviation Physiology • Structure • Equipment • Patient transport • Cases

3. History - a pop quiz • When was the first documented use of areomedical transport? • 1870: During the Franco-Prussian war 160 wounded soldiers and civilians were evacuated by hot air balloon. • When were airplanes first used for transport? • 1910 was the first privately funded fixed wing to transport patients. WW I&II saw large numbers of casulties transported to definitive medical care • When was the helicopter invented? • First flight in 1939. First rescue mission in 1945. • What war marked the advent of helicopters for medevac? • The Korean war • When was the first hospital-based helicopter program started? • 1972, Denver, Colarado

4. Aeromedical Facts • There are ~ 275 HEMS operating in the USA • ~ 4-5 in Canada • since 1950 estimated 1,000,000 lives have been saved as a result of all areomedical transport • STARS is 100% devoted to HEMS

5. Aviation Physiology • 4 laws that you need to know about: • Dalton’s Law: PT= P1 + P2+P3 … • the total atmospheric pressure is equal to the sum total of the constituents • Why does this matter? • As the atmospheric pressure decreases with altitude the partial pressure of oxygen also decreases. • As the partial pressure of oxygen decreases, oxygen saturation also decreases

6. Aviation Physiology • Boyle’s Law P1 V1 = P2 V 2 • as pressure decreases, volume increases • What is the significance? • With ascent trapped gases will expand • with descent gases will retract • Henry’s Law • the mass of gas absorbed by a mass of liquid is directly proportional to the partial pressure of gas above the liquid • Significance? • When diving the increased pressure forces gas into the bloodstream • rapid ascent causes gas to come out of solution into the bloodstream • How would this relate to air transport?

7. Aviation Physiology • Charles’ Law V1 T2 = V2 T1 • therefore temperature falls with altitude

8. Structure Sponsorship of services: • HEMS operations are costly • annual budgets of $700,000 - $ I.6 million (1986) • hospital-based • private services • public service agencies

9. Structure - Types of Missions • Primary: • sole means of transport of patient to receiving facility • Secondary: • transfer from a facility where some degree of stabilization has been done • Tertiary: • inpatient transfer

10. Structure - types of Aircraft • Single engine vs. twin engine • must be capable of lifting crew, equipment, fuel, reserves of fuel and oxygen • center of gravity must be large enough such that variations of persons and equipment inside the cabin will not interfere with the flight • capability in poor weather and at night (VFR vs IFR) • aircraft space - patient’s head and chest must be accessible to 2 crew members • patient loading • minimal maneuvering • ability to perform load with blades turning

11. Structure - Aeromedical Personnel • Variable crew composition • usually 2 members; N/N, N/P, P/M, M/M • routine physician on flight is uncommon • ~ 20% of flight have flight doc • difficult to predict which flights would benefit by having a doc on board • Evidence for the flight physician …..

12. Aeromedical Personnel - Evidence for the flight physician • Lit review found 7 papers (4 trials, 1 positions paper and 2 from really obscure journals) • All 2 articles dealt with trauma patients, 2 with all air transports • all relatively small studies (n = 300-1,169) • 1 study found a positive result based on TRISS scores and predicted vs actual mortality • 3 studies found no difference (groups similar for patient demographics, severity of injury) in mortality, ICU length of stay or hospital length of stay • largest study only powered to detect a 10% difference in mortality JAMA. 1987. Vol 257, no. 23, pp3246-3250 J of Trauma. 1991. Vol. 31, no. 4, pp 490-494 Ann Emerg Med. 1992. Vol. 21, no. 4, pp 375-378 Ann Emerg Med. 1995. Vol. 25, no. 2, pp. 187-192

13. Structure - Communications • Must have a full-time dispatch/link center • Who do you need link together? • Referring agent • referral physician • aircraft • flight coordination center (air traffic control) • ground services • communication center needs to follow the flight position and give directions, distances, and scene coordinates • aircraft must be able to communicate with communication center, ground EMS, air traffic control, public service units

14. Logistical Issues • Safety • 1980-1985: 47 deaths of flight crew members • an emphasis on safety and increased regulations has decreased “accidents” • Safety standards: • crew training • daily craft inspections • impartiality of the pilot • properly stowed equipment and secured patient • limits on work hours

15. Logistical Issues • Notification: • Level of response: status, stand-by, confirmed request • Preflight : accurate geographic location and possible hazards • Public safety agencies to provide crowd and traffic control • Landing Zones: • 60x60 foot area - day • 100x100 foot area - night • clear of loose debris • marked by lights/flares • Approaching the helicopter • only when rotor blades at complete stop • approach from the front NEVER the tail • follow directions of the pilot

16. Logistics • In general aeromedical transport is not indicated unless it decreases transport time or delivers medical expertise or equipment • how do you know transport times? • Hopefully a chart of call exists • helicopter flying time: • ~ 120 mph • double flying time • add 10-30 minutes at the scene • add 5-10 minutes for dispatch time

17. Equipment • Physical Exam limitations • heart sounds, breath sounds, palpation of carotid pulse very difficult • Communication limitations • difficult for the crew to hear if patient has concerns • Electronic monitoring • cardiac monitoring • blood pressure • endtidal CO2 • temperature • oxygen saturation • Therapeutic devices • defibrillator, intraaortic balloon pump, respirator • ETT, air splints, iv infusions, pacemakers

18. Patient Transport TRAUMA PATIENTS : 1. Scene Calls • appears to be the most justifies use of helicopter transport • early studies showed improved actual mortality vs predicted. • 2 major studies (N= 300, N = 1273) of helicopter vs ground • predicted mortality based on TRISS (TS, ISS & mechanism) • 52% reduction in predicted mortality and 21% redcution in expected mortality reported (JAMA . 1983;249(22): 3047-3051 Ann Emerg Med.1985; 14(9): 859-864) • hospital/ICU length of stay (use log regression to account for differences in study groups)

19. Transport - Scene calls • more recent studies have looked at more objective markers • larger studies (N= 20-22,000), retrospective • both found air transported patients had higher ISS, lower TS, lower mean BP & lower GCS • 1 study showed no difference in mortality but did not comment on hospital/ICU length of stay (used log regression to account for differences in study populations) J of Trauma. 1998;45(1): 140-146 • another study found a trend toward decreased mortality rate in the helicopter group • stat sig improvement in mortality for patients with TS 5-12 & ISS 21-30 in the helicopter population J of trauma. 1997; 43(6): 940-946

20. Trauma - Scene calls Guidelines • Should be dispatched for seriously injured patients who are salvageable • not justified if flight does not reduce transport time unless providing equipment or skills • patient should be transported to nearest appropriate hospital • should be integrated into hospital EMS • dispatched within medical guidelines established by regional EMS

21. Transport Trauma - interfacility Transport • 3 major studies: 1. prospective cohort , N= 200, measured actual vs predicted mortality air transport had 25% decrease in predicted mortality j of Trauma. 1989; 29(6): 789-793 2. Retrospective case series, N = 916 cases were reviewed and categorized into essential, helpful or “not a factor” with respect to air transport. ~ 27% were determined to be essential/helpful Arch Surg 1987; 122: 992-996 3. Prospective cohort, N = 1,387 ( 153 by ground), end point 30 day mortality no difference in 30 day mortality J of Trauma. 1998; 45(4): 785-790

22. Transport Trauma - Urban • 2 major studies: 1. Retrospective, N = 606 lower TS and GCS in helicopter group longer transport times within the city limits mortality increased 18% vs 13% (stat sig) J of Trauma. 1988;28(8): 1127-1134 2. J of Trauma. 1984; 24: 946

23. Patient Transfer Cardiac • Reasons for concerns: • hypoxia at high altitude creates increased HR and RR and ? MVO2 • flight increases plasma catecholamines (Circulation. 1998;78(Suppl 2): 188) • Numerous studies have looked at this patient group • most are case series with historical controls • in general show no increased mortality en route or to hospital discharge • ~ 12-20% have complication en route (hypotension, arrhythmia, third degree heart block) • no increase in bleeding complications when transported post lytic (very small series) • no improved rates of outcome reported

24. Transport STROKE • with the advent of tPA for the treatment of stroke rapid transport is becoming an isue • 2 studies 1. Transport of stroke patient within 24 hr of symptoms n= 73 no significant deterioration of symptoms, no patient received tPA on arrival to hospital, 93% of patient felt they benefited from HEMS 2. Transport of patient after tPA n = 24 no neurologic or systemic complications Stroke. 1999;30:2366-2368 Stroke. 1999;30:2580-2584

25. Transport Preterm Labor • Air Transport not recommended if: • previous precipitous delivery • cervix dilated 7cm or more • rapidly progressing labor (major change in Cx between time of dispatch and arrival of AMC) • other medical reason not to fly • Indications for transport: • Gestational age 24-32 wk • evidence of PTL with regular uterine contractions • +/- PROM • NOT fully dilated/ presenting part at perineum • caution if Cervix > 7 cm • patient accepted at tertiary care center

26. Transport Preterm labor • Prior to arrival of AMC (phone orders) • vag exam, ? Dilation , effacement, and fetal heart tones • Iv access and rehydrate up to 500ml • indomethacin 100mg pr • Steroids - 24 mg IM Betamethasone • iv magnesium 4 grm over 30 minutes then 2 gr/hr • On arrival of AMC • repeat vag exam • reconsider transport if rapidly progressing or Cx > 7 cm • Cardiac and O2 monitoring

27. Transport Preterm labor • Inflight • transfer with mom’s head in rear • semi-sitting ofr left lat decub • O2 sat > 95% • monitor BP : stop Mg if BP < 100 or HR < 100 • if patient destas: stop Mg, sit up, lower flight altitude, give O2 • monitor contractions • Imminent delivery • suspect if stacking contractions, ROM en route, increased bleeding • expect a breech presentation (~ 40% of prems)

28. Transport Burns • increase in fluid loss with decrease atmospheric humidity • prone to hypothermia with decreased ambient temperature Decompression sickness • maintain on 100% O2 • must fly at < 1000 feet to prevent further dysbarism

29. Transport • General Indications • when ground transport time is excessive • access to needed care is not accessible locally and delay in receiving care will have adverse outcome • local resources inappropriate for transport (ie most rural communities have limitted resources and BLS crews only) • Contraindications • patient is terminally ill with no medically treatable problem • DNR • code in progress

30. Transport • Relative Contraindications • active labor • diving within 12-24 hr • violent/dangerous patient • gas trapping in enclosed body compartment • condition overwhelms equipment or resources of the aeromedical program

31. Transport • Optimal mode of transport • urban: ground ambulance • rural: air or ground ambulance • long range: fixed wing

32. Transport Comparison of ground vs rotor vs fixed wing

33. Transport Ground Ambulance vs rotor vs fixed wing

34. “ I always believed that the helicopter would be an outstanding vehicle for the greatest variety of life-saving missions, and now, near the close of my life, I have the satisfaction of knowing that this proved to be true” - Igor Sikorsky , 1972