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Chapter 21: Aerospace Medicine
Aerospace Medicine: Hypoxia
LTC Brian Campbell, MC, USAIntroduction: Oxygen makes up approximately 20% of the air we breathe. As ambient atmospheric
pressure decreases with increased altitude, partial pressures of oxygen also drop. This results in decreased
oxygenation of the blood and tissue hypoxia. Healthy individuals can easily tolerate ambient pressures of
10,000 feet above mean sea level (MSL) for prolonged periods without hypoxic effects. However, everyone
will eventually become impaired above 10,000 feet. Rapid decompression at extreme altitudes may result
in death. See also related injuries such as acute mountain sickness, high altitude pulmonary edema, high
altitude cerebral edema hypoxia associated with diving. Risk Factor: Underlying pulmonary disease (acute
or chronic).
Subjective: Symptoms
Variable from person to person, but consistent in an individual across exposures; impaired judgement, thinking,
and vision (particularly color vision); paresthesias, especially of the face and hands, are common.
Focused History: When did symptoms start? (acute onset with change in altitude is typical) Have you
had a fever or other signs of illness prior to this flight? (pulmonary disease is risk factor, or may suggest
alternate diagnosis) Have you been diving or breathing compressed air in the last 48 hours? (may suggest
decompression sickness [DCS]) Have you been flying? If so, do you know the cabin altitude of the flight?
(>10,000 feet is typical) Are you taking any drugs or medications of any kind? (consider substance abuse,
drug reaction or allergic reaction)
Objective: Signs
Using Basic Tools: Lack of fine motor control; personality changes (e.g., withdrawn, violent, or highly
flamboyant activity; inattentiveness or absence periods; respiratory rate and pulse may increase; seizure
activity is possible.
Assessment: Resolution of signs and symptoms with return to lower altitudes or treatment with oxygen
confirms the diagnosis.
Differential Diagnosis:
DCS - may rule out if not > 18,000 feet MSL and negative history of breathing compressed air within last
48 hours
Substance abuse - may rule out if no history or other evidence/suspicion of taking drugs, medications,
“nutritional supplements”
Allergic or idiopathic reaction to prescription or OTC medications (including “nutritional supplements”) - may
rule out if not taking any of these substances)
Atypical seizure activity - must consider if positive history of seizure disorder or history of head trauma
involving loss of consciousness within the last 10 years
Plan:
Treatment
Primary: Supplemental oxygen under pressure via fitted mask.
Alternative: Increase oxygen concentration of inspired air by any other means (different masks, etc.).
Primitive: Increase ambient pressure by decreasing altitude or adjusting cabin altitude