Blair Munford

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
NRMA CareFlight 3

4. Stresses of Flight
q Hypoxia q Immobility
q Dysbarism q Motion sickness
q Thermal stress q Spacial Disorientation
q Dehydration q Third Spacing
q Noise q Anxiety
q Vibration q Dystemporism
q G forces q Fatigue
NRMA CareFlight 4

5. FOUR GAS LAWS
q Boyles Law q Henry’s Law
P1V1 = P2V2 Cdissolved = k.Pgaseous
Trapped Gas Evolved Gas Disorders
Disorders
q Charles’ Law
qDalton’s Law V1/V2 = T1/T2
Ptot = P1 + P2 . . . + Pn (or Blair’s
Hypoxia! modification)
P.V = k.T
NRMA CareFlight 5

6. THE ATMOSPHERE: Physical
q TROPOSPHERE: 0 (SL) -15,000m
– Contains clouds. Temperature falls with
altitude.
q STRATOSPHERE: 15,000 - 50,000m
– Includes ozone layer
q MESOSPHERE: 50,000 - 80,000m
(50-80km)
q IONOSPHERE: 80 - 650 km
– UV & gamma irradiation produces ions
q EXOSPHERE: 650 - 9,500 km.
NRMA CareFlight 6

7. The Earth’s Atmosphere
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8. AVIATION PHYSIOLOGY EXAM?
Q1. Identify the four components of the atmosphere.
Air, Clouds,
Birds, &
Helicopters?
NRMA CareFlight 8

9. THE ATMOSPHERE:
Chemical
GAS % OF ATM P (SL)
N2 78% 593mm Hg
O2 20.95% 160mm Hg
Ar 0.9% 7mm Hg
Other 0.05% 0.35mm Hg
NRMA CareFlight 9

10. ALTITUDE TABLE
Altitude Pressure pO2 Temp Volume
(feet) (mm Hg) (mm Hg) (Celcius) Change
SL 760 159 15.0 ---
1000 733 153 13.0 3.1%
2000 706 148 11.0 7.6%
4000 656 137 7.1 15.8%
7000 586 122 1.2 29.7%
10,000 523 110 -4.8 45%
20,000 349 73 -24.6 117%
NRMA CareFlight 10

11. THE ATMOSPHERE:
Physiological
q Efficient (Physiological) zone
– 0-12,000’ (0-4000m) Pb 760 - 480 mmHg
q (Physiological) Deficiency zone
– 12-45,000’ Pb 480 - 110 mmHg
q Partial Space Equivalent Zone
– 45-600,000’. Pressurisation mandatory
q Total Space Equivalent Zone
– >600,000’ (200km). Weightlessness
NRMA CareFlight 11

12. HYPOXIA
“The Hidden Enemy of Air Medical Transport”
q PATIENTS q AIRCREW
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13. CLASSIFICATION OF HYPOXIA
q Hypoxic Hypoxia
q Anaemic Hypoxia
q Stagnant Hypoxia
q Histotoxic Hypoxia
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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.
NRMA CareFlight 15

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
NRMA CareFlight 20

21. Trapped Gas Problems with
Equipment
q Endotracheal/tracheostomy tube cuffs
q Sengstarken-Blakemore tubes
q Swann-Ganz balloons
q Pneumatic antishock garments (MAST)
q Air splints
q Drainage bags
– Nasogastric/intercostal/colostomy
NRMA CareFlight 21

22. EVOLVED GAS DISORDERS
q Remember Henry’s Law
q Problem is dissolved N2
(1.0 -1.5 L)
q Requires decompression
– Abrupt : Universal risk
– Planned : At risk individuals only
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23. RISK FACTORS FOR
EVOLVED GAS DISORDERS
q DIVING (& Hyperbaric
training)
q Prolonged altitude exposure
q Obesity
q Alcohol
q Dehydration
q Cold
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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
NRMA CareFlight 24

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’
NRMA CareFlight 26

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
NRMA CareFlight 27

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
NRMA CareFlight 29

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.
NRMA CareFlight 30

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
NRMA CareFlight 31

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
NRMA CareFlight 32

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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34. MOTION SICKNESS
q Variable susceptibility
Precipitating factors include:
q Turbulence
q Spatial disorientation
q Hot/stuffy environment
q Hunger or oversatiation
q Fear or unpleasant stimuli
q Medications
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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
NRMA CareFlight 35

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
NRMA CareFlight 36

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

38. FATIGUE I:
THE RISK FACTORS
q Remember the avoidable:
D*E*A*T*H
q Drugs
q Exhaustion
q Alcohol
q Tobacco
q Hypoglycaemia
NRMA CareFlight 38

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

40. THE END
Any Questions?