Aeromedical Transportation
Sarah McPherson & Dr. A Abbi
November 1, 2001
Outline






History
Aviation Physiology
Structure
Equipment
Patient transport
Cases
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
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
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
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?
Aviation Physiology

Charles’ Law
V1 T2 = V2 T1
• therefore temperature falls with altitude
Structure
Sponsorship of services:
•
•
•
•
•
HEMS operations are costly
annual budgets of $700,000 - $ I.6 million (1986)
hospital-based
private services
public service agencies
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
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
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 …..
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
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
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
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
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
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
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)
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
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
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
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
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
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
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
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
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)
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
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
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
Transport

Optimal mode of transport
• urban: ground ambulance
• rural: air or ground ambulance
• long range: fixed wing
Transport
Comparison of ground
vs rotor vs fixed wing
Transport
Ground Ambulance
vs rotor vs fixed wing
“ 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