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Make the Diagnosis: Does This Patient Have Acute Mountain Sickness?

Prior Probability of Acute Mountain Sickness Among Travelers at High Altitude

Traveling to high altitude for recreational purposes has become increasingly popular but risks the development of acute mountain sickness (AMS). Findings from a meta-analysis indicate that AMS may affect approximately 33% of individuals ascending to 3500 m (11 500 ft) and 66% of those reaching elevations above 6000 m (19 700 ft). Acute mountain sickness affects more than 25% of individuals ascending to 3500 m (11 500 ft) and more than 50% of those reaching elevations above 6000 m (19 700 ft).

Population Among Whom Acute Mountain Sickness Should Be Considered

Any traveler at high altitude, including healthy travelers, can get AMS, which can start within hours after arriving at high altitude. The most common symptoms will create functional impairment that affects the activities of the traveler. Symptoms include headache, loss of appetite, nausea, vomiting, dizziness, fatigue, and sleep disturbances. Typically, symptoms resolve spontaneously after 18 to 36 hours without requiring descent to lower altitude. A very small percentage (< 1%) of individuals have progression to life-threatening high-altitude cerebral edema that causes altered level of consciousness and ataxia.

The most important risk factors for AMS are a prior episode of AMS with reascent under similar conditions (for example, similar rapidity of ascent, absolute altitude, no medical prophylaxis). Travelers who are older than 50 years of age have a lower risk of AMS than those younger than 50 years (risk = 0.49; 95% CI, 0.27 to 0.87).

The most important modifiable behaviors are the altitude attained and speed of ascent. Ascents that are faster than 400 m per day (1300 ft/d) have a higher risk for development of AMS (OR, 4.69; 95% CI, 2.79-7.90), whereas slower ascents have a lower risk (OR, 0.30; 95% CI, 0.20-0.44). Acute mountain sickness is less likely to develop when there has been preacclimatization (ie, previous exposure to altitude within 1-2 months) or medical prophylaxis with acetazolamide or dexamethasone.

Assessing the Likelihood That a Traveler Has Acute Mountain Sickness

The simplest way to assess for the likelihood of AMS is the clinical function score (Table 104-1), in which a traveler assesses his or her ability to perform daily activities, from no reduction of daily activities (score = 0) to mild reduction (score = 1), moderate reduction (score = 2), or severe reduction (eg, bed rest; score = 3). While symptoms may develop within 6 hours of arriving at high altitudes, early symptoms might be confounded by travel fatigue or responses to acute hypoxia. For travelers who self-assess themselves as having a moderate reduction in daily activities, assessment with the Lake Louise Questionnaire Score (LLQS); (Table 104-2) after 6 hours at altitude might quantify the severity of AMS. The LLQS may be self-administered or a travel companion can review the questions with the affected traveler. Suggested LLQS thresholds are ...

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