6-37
NOTES: DCS is a danger in any flying operation that requires ascent to 18,000 feet MSL or above. Rapid
return to lower altitudes in HALO missions mitigates the threat to some degree, but compression in a
hyperbaric chamber is required in any DCS case. Neurologic DCS is life threatening and should be treated as
a true medical emergency. Consider any episode of DCS as grounds for temporary restriction of special duty
status until cleared by competent medical authority.
Chapter 22: High Altitude Illnesses
High Altitude Illnesses: Acute Mountain Sickness
COL Paul Rock, MC, USA & LTC Brian Campbell, MC, USAIntroduction: Acute mountain sickness (AMS) is a short-lived (days to a week) illness that occurs in people
from low altitude (less than 5000 ft) who travel rapidly to higher areas (usually more than 8000 - 9000 ft) and
remain there for more than several hours. It is caused by the decreased amount of oxygen available at high
altitude (see Aerospace Medicine: Hypoxia). Symptoms of AMS usually go away as a person’s body adapts
to lower oxygen levels over a week to 10 days (altitude acclimatization). It is impossible to predict who will be
more susceptible to AMS. Although not life-threatening, AMS can degrade physical and mental performance.
Additionally, AMS can progress to more serious altitude illness such as high altitude cerebral edema (HACE)
and high altitude pulmonary edema (HAPE).
Subjective: Symptoms
Similar to a alcoholic “hangover”- headache (often severe), nausea (with or without vomiting), fatigue,
decreased appetite, disturbed sleep. Symptoms begin within 3 to 24 hours after ascending to a higher
elevation and are most severe in the first 24 to 48 hours.
Focused History: When did symptoms begin? (typically start within 24 hours after traveling to higher
altitude) Did you have these symptoms or an illness before going to higher altitude? (affirmative answer
suggests viral illness or other preexisting condition) Have you taken any medications, drugs or alcohol?
(Intoxication with these substances can cause symptoms similar to AMS.) Have you been in a tent, cave or
vehicle with a stove or motor running? (Carbon monoxide poisoning can cause similar symptoms.) Do you
have a cough or difficulty breathing? (suggests HAPE) How is your coordination? Have you been stumbling
or falling? (suggests HACE)
Objective: Signs
Using Basic Tools: Patient appears 'sick'; decreased urination; poor balance (truncal ataxia) when carrying
backpack; mild swelling (edema) in the hands, feet and/or face (‘puffy’ around the eyes.)
Using Advanced Tools: Pulse oxygen levels will be lower with AMS or other altitude illnesses.
Assessment: Diagnosis is made on basis of history.
Differential Diagnosis
Early HACE - significant ataxia (cannot do ‘heel-to-toe walk’); swelling of optic nerve (papilledema).
Coexistent HAPE - cough; rales; frothy, pink, or blood-tinged sputum.
Other causes of headache (migraine, cluster, or tension headache; viral syndrome; meningitis; head trauma;
etc.) Symptoms before ascending to altitude - stiff neck, fever or increased white cell count; history of head
trauma.
Intoxication - history of ingesting medications, recreational drugs, alcohol. (see Toxicology chapter)
Carbon monoxide poisoning - history of exposure to combustion fumes, occasional cherry-red skin color.
(see Toxicology chapter)
Hypothermia - lack of headache and nausea, decreased body temperature. (see Cold Illneses: Hyporthermia)
Hyperthermia and/or dehydration - history of decreased fluid intake, elevated body temperature or tenting of
skin. (see Heat Related Illnesses chapter)