Hypoxia definition
A lack of oxygen to the tissues
sufficient to cause impairment of function
4 types of tissue hypoxia
- Hypoxic hypoxia
- Hypaemic hypoxia
- Stagnant hypoxia
- Histotoxic hypoxia
Hypoxic hypoxia
Reduced diffusion of oxygen from alveoli to blood
Aviation causes:
- altitude (hypobaric hypoxia)
- oxygen system failure
Medical causes:
- hypoventilation
- respiratory pathology (acute or chronic)
Hypaemic hypoxia
Reduced ability of blood to transport oxygen
Aviation causes:
- carbon monoxide
Medical causes:
- anaemia
- haemorrhage
- Hb abnormalities
Stagnant hypoxia
Reduced blood flow to tissues
Aviation causes:
- “pulling G”
- cold
Medical causes:
- shock
- arterial disease
- cardiac failure
- emboli
Histotoxic hypoxia
The inability of cells to utilise oxygen
Aviation causes:
- toxic smoke and fumes
- hydrogen cyanide
- carbon monoxide
Medical causes
- alcohol
- poisoning
Causes of hypoxia in flight
- Ascent to altitude without oxygen
- Failure of oxygen systems
- Decompression of cabin at high altitude
- Toxic fumes
Summary of Physiological Oxygen Requirements
Time of Useful Consciousness
The period of time between onset of exposure to reduced oxygen and the point when performance is impaired such that effective action is impossible
Summary of Aircrew O2 Requirements
Summary of PAX O2 Requirements
TUC depends on 4 things
Altitude
Time of exposure
Breathing gas
Rate of ascent
Factors affecting Tolerance to Hypoxia
Drugs
Alcohol & Hangover
Smoking
Other Illnesses
Physical fitness
Rate of ascent
Exercise at altitude
Stress and workload
Cold
Fatigue
Oxygen Paradox
A temporary worsening of hypoxia symptoms with the re-introduction of oxygen
- usually mild with flushing and poor performance
- occasionally severe with potential for spasms &/or loss of consciousness
Problems with Oxygen
- Oxygen toxicity
- Oxygen paradox
- Oxygen trapping
- oxygen ear
- atelectasis - Mission endurance
- Fire hazard
Effects of hyperventilation
- Increased pH decreases plasma [Ca2+]
* disturbance of nerve & muscle function
* paraesthesia in lips and fingers
* carpo-pedal spasm - Cerebral vasoconstriction
Aviation Related Causes of Hyperventilation
- Hypoxia -“hypoxic ventilatory response”
- Emotion -pain, stress, anxiety
- Vibration
- Motion sickness
- Anti-G straining
- Pressure breathing
Why do Hypoxia Training?
- Awareness – of symptoms
- Demonstration – of impairment
- Indoctrination – recovery actions
- Rehearsal – checklists and drills
- Familiarity – oxygen equipment
- International obligations - interoperability (AFIC)
Types of Hypoxia Training
- Hypobaric chamber
* Traditional
* CADO - Normobaric (gas mix)
* Reduced Oxygen Breathing Environment (ROBE)
* Reduced Oxygen Breathing Device (ROBD)
Risks of Hypoxia Training -Hypobaric
Otic/pulmonary barotrauma
Decompression illness
Hyperventilation
Syncope
Effects on unrecognised intercurrent illnesses
Pre-and post-training restrictions
