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 III 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
• Daltons Law
• PT P1 P2P3
• 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

• Boyles 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
• Henrys 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 - patients 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 .
  1983249(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. 199845(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. 198828(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. 199878(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. 1999302366-2368 Stroke.
  1999302580-2584

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 gt 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
  gt 7 cm
• Cardiac and O2 monitoring

27
Transport

• Preterm labor
• Inflight
• transfer with moms head in rear
• semi-sitting ofr left lat decub
• O2 sat gt 95
• monitor BP stop Mg if BP lt 100 or HR lt 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 lt 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