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CAQ Review

Altitude Illness

Alex, James MD

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Current Sports Medicine Reports: March/April 2015 - Volume 14 - Issue 2 - p 82-83
doi: 10.1249/JSR.0000000000000127
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Altitude Illness

Definitions: All in the setting of recent altitude gain to >2500 m (5).

Acute Mountain Sickness (AMS): headache and at least one of the following:

  • 1. Gastrointestinal dysfunction (nausea, vomiting, anorexia)
  • 2. Fatigue or weakness
  • 3. Dizziness or lightheadedness
  • 4. Insomnia

High-Altitude Cerebral Edema (HACE):

  • In a patient with AMS or high altitude pulmonary edema: either ataxia or altered mental status (or both)
  • In a patient without AMS: both ataxia and altered mental status

High-Altitude Pulmonary Edema (HAPE):

  • At least two symptoms
    • 1. Dyspnea at rest
    • 2. Cough
    • 3. Weakness or decreased exercise performance
    • 4. Chest tightness or congestion


  • At least two signs
    • 1. Crackles or wheezing in at least one lung field
    • 2. Central cyanosis
    • 3. Tachypnea
    • 4. Tachycardia

Key Point: AMS and HACE are considered ends of the same pathophysiologic spectrum (5).


  • Estimates of overall incidence of altitude illness range from 25% to 85% with HAPE and HACE accounting for a fraction of cases at incidence ranging from 0.1% to 4% (1).
  • Risk factors: faster ascent, age <50 years, lower altitude home, prior history of high-altitude illness, male gender (HAPE only) (1,2).
  • Noncontributory factors: physical fitness, pregnancy, mild chronic obstructive pulmonary disease (COPD), hypertension, coronary artery disease (CAD) (2).

Important Differential Diagnoses:

  • HAPE: pneumonia, asthma, pulmonary embolism, myocardial infarction, heart failure (2).
  • AMS/HACE: viral/bacterial infection, dehydration, hypothermia, carbon monoxide poisoning (from enclosed camp stoves/fires), alcohol intoxication, hyponatremia (2).

*Note: Infection susceptibility increases at altitude with immunosuppression from UV radiation (increases 11% to 19% per 1000 m), repetitive exertion, malnutrition, and insomnia (3).


The most important modifiable risk factor for all altitude illness is the rate of ascent. Ascent ≤500 m·d−1 when above 2500 m, with a rest day every 3 to 4 d, is recommended (4). Also avoid direct transport to >2750 m (2).

Medication Prophylaxis: Only advised in patients with a history of altitude illness and/or cannot follow either of the aforementioned preventive measures (4).

*AMS/HACE Prophylaxis (1,2,4):

First line: acetazolamide 125 mg BID starting 24 h before ascent, until descent. Note: Avoid in patients with sulfonamide anaphylaxis. World Anti-Doping Agency (WADA) banned (3).

Second line: dexamethasone 4 mg every 12 h starting on the day of ascent until descent or 2 to 3 d at target. WADA banned (3).

*HAPE Prophylaxis (1,2,4):

First line: nifedipine extended release 20 to 30 mg every 12 h. WADA approved but increases HR and decreases peak performance at altitude (3).

Second line: salmeterol 125 μg BID. WADA status changes frequently (3).

*Used to supplement nifedipine, not recommended as monotherapy.

Third line: tadalafil 10 mg BID or dexamethasone 8 mg BID. WADA monitoring PDE5 inhibitors for potential ban (3).


Key Principles:

  1. AMS is self-limiting and will resolve with stable elevation, though more quickly with descent and/or medication treatment (4).
  2. HAPE and HACE are emergencies requiring immediate descent, ideally with minimal patient exertion. Other treatment options remain effective if descent is impossible (1–4).

AMS Treatment:

First line: stop ascent or descent until symptoms resolve (1,2,4).

Second line: NSAIDs for headache or prochlorperazine 10 mg every 6 h versus promethazine 25 to 50 mg every 6 h for nausea (2).

Third line: Dexamethasone 4 mg every 6 h for moderate-severe AMS or acetazolamide 250 mg BID for mild-moderate AMS (1,2,4).

HAPE Treatment (2,4):

First line: descent, 1000 m or until symptoms resolve.

Second line: supplemental oxygen and/or portable hyperbaric chamber.

Third line: nifedipine extended release 30 mg every 12 h.

HACE Treatment (1,2,4):

First line: descent, 1000 m or until symptoms resolve.

Second line: supplemental oxygen and/or portable hyperbaric chamber.

Third line: dexamethasone 8 mg then 4 mg every 6 h until symptoms resolve.

Other Considerations:

  • Contraindications to high altitude travel: sickle cell anemia, severe COPD, uncompensated coronary heart failure, and pulmonary artery hypertension (1).

The author declares no conflicts of interest and does not have any financial disclosures.


1. Fiore DC, Hall S, Shoja P. Altitude illness: risk factors, prevention, presentation, and treatment. Am. Fam. Physician 2010; 82: 1103–10.
2. Hacket PH, Roach RC. High altitude illness. N. Engl. J. Med. 2001; 345: 107–14.
3. Koehle MS, Cheng I, Sporer B. Canadian Academy of Sport and Exercise Medicine Position Statement: athletes at high altitude. Clin. J. Sports Med. 2014; 24: 120–7.
4. Luks AM, McIntosh SE, Grissom CK, et al. Wilderness Medical Society consensus guidelines for the prevention and treatment of acute altitude illness. Wilderness Environ. Med. 2010; 21: 146–55.
5. Sutton JR, Coates G, Houston CS. Hypoxia and Mountain Medicine. 1st ed. Burlington: Queen City Printers, 1992.
Copyright © 2015 by the American College of Sports Medicine.