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Aviation Medicine
1. AVIATION PHYSIOLOGY
The Scientific Foundation of
Air Medical Transport
Blair Munford, FANZCA
NRMA CareFlight/New South
Wales Medical Retrieval Service
2. Aviation Physiology and
Critical Care Transport
RELEVANT TO:
q Mode of Transport
– Road vs rotorwing vs fixed wing
q Patient Selection
q Patient Treatment
q Aircrew Issues
– Risks, precautions, fitness to fly.
NRMA CareFlight 2
3. Aviation Medicine vs Aeromedicine
vs Air Medicine
A V IA T IO N P H Y S IO L O G Y
A V IA T IO N A IR
M E D IC IN E M E D IC IN E
O c c u p a t io n a l C r itic a l C a r e &
H e a lt h E m e r g e n c y M e d ic in e
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14. EFFECTS OF HYPOXIA
q CENTRAL NERVOUS SYSTEM
– Progressive dysfunction starting with
retina & higher centres.
q RESPIRATORY SYSTEM
– Increased MV with decreased PaCO2.
q CARDIOVASCULAR SYSTEM
– HR increases followed by peripheral
vasoconstriction & cerebral vasodilatation
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15. STAGES OF HYPOXIA
q INDIFFERENT q DISTURBANCE
<10,000’, SaO2>90% 15-20,000’ SaO2 70-80%
HR & RR increase Compensatory failure
Effect on night vision Significant CNS changes
q COMPENSATED q CRITICAL
10-15,000’ SaO2 80-90% 20,000’+ SaO2 <70%
CO & sBP rise Rapid onset of coma &
CNS symptoms seizures; death likely.
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16. OXYGEN THERAPY
q ALVEOLAR GAS EQUATION
PAO2 = PiO2 - PACO2 / R + F
q FiO2 CALCULATION
FiO2(2) = FiO2(1) x P1 / P2
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17. DYSBARISM
q TRAPPED GAS DISORDERS
(Boyles Law)
q EVOLVED GAS DISORDERS
(Henry’s Law)
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18. TRAPPED GAS DISORDERS
q Physiological Air Spaces
q Pathological Air Spaces
q Technological Air Spaces
(Equipment)
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19. Trapped Gas Disorders I:
“Physiological”
q Barotitis Media q Barodentalgia
– Ascending squeeze – Ascending squeeze
– Descending squeeze only
q Barosinusitis q Baroenteralgia
– Ascending squeeze – Ascending squeeze
– Descending squeeze only
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20. Trapped Gas Disorders II:
“Pathological”
q Intracranial air
q Open eye injury
q Pneumothorax
q Emphysema/bullae/
asthma
q Bowel obstruction or
rupture
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24. DECOMPRESSION SICKNESS
Effects include:
q Joints
– “The Bends”
q Skin - Bariobariatrauma
q Central Nervous System
q Arterial Gas Embolism !!!
– “The chokes” - abrupt
decompression
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25. CABIN PRESSURISATION I:
PRINCIPLES
q Applicable to fixed wing only
q Partial defense against:
– Hypoxia
– Dysbarism
q Creates artificial “Cabin Altitude”
q Cabin altitude dependant on:
– Actual altitude
– Maximal pressure differential
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26. CABIN PRESSURISATION I:
CALCULATIONS
q Example I - Lear 35
Maximum cabin pressure differential 430mm Hg
So @ 40,000’ (=141 mm Hg) can maintain cabin
altitude of 570 mmHg = 8000’
q Example II - King Air 200.
Sea level cabin altitude requested. Max cabin
pressure differential = 350 mm Hg. So can fly
at 410 mm Hg = 16,000’
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27. THERMAL STRESS I: PRINCIPLES
q Remember mechanisms of heat loss:
CONVECTION
CONDUCTION
EVAPORATION
RADIATION
q Outside air temperature
– drops 2 degrees C per 1000’ rise
q Helo patients also at risk of temp rise
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28. THERMAL STRESS I:
Special Risk Patients
q Paralysed/Sedated
q Intoxicated
q Polyinfused/transfused
q Immersion or other wet
q Pre existing hypothermia
q Burns patients
q Prolonged transports
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29. HUMIDITY & DEHYDRATION
q Water vapour content falls with
increasing altitude & decreasing temp.
q Pressurised aircraft has WVP of outside
pressure not cabin pressure
EFFECTS ON
q RESPIRATORY SYSTEM
q Other mucus membranes
q Endocrine/renal/CVS axis
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30. NOISE
q Major hinderance to patient care
q Level: Helo > Fixed wing > Road
q Noise interferes with
– Communication
– Patient assessment - e.g auscultation
q Hearing protection & communications
technology mandatory in helicopter.
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31. VIBRATION
q Interferes with:
– Patient comfort
– Metabolic Rate (increases)
– Equipment: NIBP, SaO2, etc.
q Vibration levels:
Road(bad) > Helo > FW take off > Road (good)
> FW cruise
q Vibration minimisation
– Passive vs active
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32. GRAVITATIONAL FORCES
q Levels of G force experienced:
1. Road vehicle (brake/swerve)
2. Fixed wing takeoff & landing
3. Road vehicle (normal driving)
4. Fixed wing climb/cruise/descent
5. Helicopter (all normal ops)
q Positioning may minimise effects
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33. SPACIAL DISORIENTATION
“INCORRECT PERCEPTION OF
POSITION, MOTION OR ATTITUDE”
Due to absent or incorrect input from one
or more of:
q Visual system
q Vestibular apparatus
q Proprioceptive apparatus
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35. “THIRD SPACING”
q Fluid leakage into interstitium
q Increased during transport
q Multifactorial
– VIBRATION
– G forces
– Temperature
q Effects include:
– Oedema/swelling under casts
– Effective dehydration/hypovolaemia
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36. DYSTEMPORISM
q Common name: “jet lag”
q Occurs with transmeridian travel
q Disturbance of circadian rhythm
q Sun following (westward) versus sun
shortening (eastward) travel.
q Influenced by: activity/food/alcohol
q Hypnotics for sleep restoration:
– Temazepam vs oxazepam
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37. FATIGUE I: THE PROBLEM
q Fatigue itself is a stressor
q Fatigue is also the common point of
other stressors.
q Fatigue affects judgement & perception
– INCLUDING OF FATIGUE ITSELF
q Air medical crew fatigue is a potential
killer:
– OF PATIENTS
– OF AIRCREW
NRMA CareFlight 37
39. SUMMARY
q All medical transport including by air
creates a sub optimal environment.
q Many patients may be at risk from this
exposure.
q The challenge is to provide optimal care
in spite of the environment
q Knowledge of the environment is the
key to achieving this.
NRMA CareFlight 39
