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# AHCP: Human Factors in Aeromedical Flight Operations

An introductory talk on flight physiology and human stressors in flight for the canidates undertaking the South African Red Cross Air Mercy Service 'Intermediate Life Support Aviation Health Care Provider' course, May 2012.
by

## Ross Hofmeyr

on 13 December 2017

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#### Transcript of AHCP: Human Factors in Aeromedical Flight Operations

Human Factors in Aeromedical Flight Operations
Dr Ross Hofmeyr - MBChB (Stell) DipPEC (SA) DA (SA) - ross@wildmedix.com
Aviation Health Care Provider Course
Red Cross Air Mercy Service

Pressure
Temperature
Vision
Fatigue
Drugs
Vibration
Noise
Gravity
Motion
Hypoxia
Acceleration
Humidity
Pressure
Decreased partial
pressure of oxygen
Ambient pressure decreases
with altitude

Two major effects:
Expansion & contraction
of gas spaces
Dalton's Law
Partial pressure of a gas is the ambient pressure multiplied by the fraction of that gas in the environment
In air: pO2 = FO2 x Pamb
= 21 kPa
Alveolar gas equation:
pAO2 = FiO2(Patm - SVPH20) - pACO2/R
Sea level: pAO2 = 0.21(100-6.3) - 5.3/0.8
= 13 kPa
Atmospheric fraction of O2 remains fairly constant at ~21% within the troposphere (FO2=0.209)
At sea level: pO2 = 0.21 x 100 kPa
(Barometric pressure at given altitude can be approximated by the formula:
PB = 101325 (1 - 2.25577.10^-5.h)^5.25588)
Ambient oxygen levels decrease with increasing altitude, a situation called high-altitude or hypobaric hypoxia.
10 000ft : pAO2 = 0.21(
65
-6.3) - 5.3/0.8
= 6 kPa
Boyle's Law:

P1V1 = P2V2
All air spaces are affected:

Ears
Sinuses
Teeth (Barodontalgia)
Gastrointestinal tract
Pathological air collections
Non-linear relationship

Greatest pressure changes occur closer to the ground
Don't
fly with a cold

Avoid carbonated drinks

Avoid foods causing increased flatus

Equalize
early and often
Decompression sickness
Formation of nitrogen bubbles due to rapid ascent
Mechanical effects of bubbles cause symptoms
First described in 1670 by Boyle; predicted in aviators in 1917
First manifested clinical problems in WWII

Factors influencing DCS:
Altitude - very rare below 18 000 ft
Duration of exposure
Rate of ascent
Body fat and fitness
Use of denitrogentation
Clinical manifestations of DCS:

Musculoskeletal - Joint & muscle pain

Pulmonary - "Chokes", dry cough, substernal pain
Neurological - scotoma, paresthesia, paralysis
Descend!
Visual disturbances
High contrast environments
Blind spots caused by glare
Inability to discern normal tissue colours
Dark adaptation and light availability in night operations

Flicker vertigo
Gravity
You can't escape... it's the law!
Altered G-forces during aircraft
maneuvering and turbulence
Protect yourself and the patient

Exacerbated by aircraft attitude on ascent

Consider patient positioning based on pathology:

Cardiac
Obstetric
Thermal stressors
Heat exchange
Wind Chill
Humidity
Lower atmosphere: 1C for every 100m height gain

Average temperatures:
Sea level: 15C
10 000 ft: -5C
30 000 ft: -50C
Aircraft aircon inoperable unless engines are running!
Sorry... you can't open the windows!
Beware of solar heating and injury
Rapid decrease in humidity with increasing altitude

Aircraft A/C further dries air

Difficult to humidify gasses due to operational constraints
Problems:

Increased insensible fluid losses

Thickened secretions

Heat loss
(NB: respiratory and dressings, eg burns)

Eye and mucous membrane irritation
Noise
Sound vs. noise vs. signal

Noise directly causes stress and fatigue

Stethoscope = "Guessing tube"

Conversation is difficult above 85dB - the threshold for permanent damage from prolonged exposure.

Ear protection (for patients and crew) should be considered mandatory
Vibration
Direct cause of fatigue and increased stress
Blend of high- and low-frequency vibration on aircraft
Rotor >> Fixed-wing

Effects
Fatigue
Discomfort
Diminished visual acuity
Diminished proprioception
Chest pain
Dysrhythmias
Beware problems with equipment
Eg. drip rates and NIBP
Cushion and secure!
Motion sickness
"Two types of aircrew - those that admit to getting airsickness and those that lie!"

Dysequillibrium between visual, proprioceptive and vestibular inputs
Certain people predisposed
Improves with time and exposure

Avoid contributing factors:
Alcohol and drugs
Fatigue
Hunger
Known trigger foods

Management:
Premedicate if you know you have a high risk
Enhance visual and proprioceptive inputs
Self- imposed stressors
Illness
Injuries
Stress
Fear
Medications
Drugs
Alcohol
Caffeine
Hypoglycaemia
Smoking
Confined space
YOYO-MF
Difficult to reposition patient
Procedures very challenging