Preventing Acute Mountain Sickness: Feeling Good While High
Source: Dumont L, Madirosoff C, Tramer MR. BMJ 2000;321: 267-272.
Dumont and colleagues performed a systematic literature review in order to evaluate the evidence for and against pharmacologic prevention of acute mountain sickness (AMS). Thirty-three trials were analyzed1 (extracted data is posted at www.hcuge.cch/anesthesie/anglais/research/ammtrials.htm). Approximately 523 subjects received one of 13 interventions while 519 received a placebo. The mean trial size was only 15 subjects per group, and only 17 trials had adequate blinding.
In eight trials with ascent to higher than 4000 m (>13,123 ft), total daily doses of dexamethasone of 8 mg, 12 mg, and 16 mg were each associated with greater efficacy in prevention of AMS than placebo; daily doses of dexamethasone of 0.5 mg and 2 mg were ineffective in a single trial. Similarly, in nine trials with ascent to higher than 4000 m, a total daily dose of 750 mg of acetazolamide was superior to placebo, while 500 mg was not. While there was a direct relationship between the incidence of AMS and the rate of ascent, both dexamethasone and acetazolamide were effective regardless of ascent rate above 500 m (1640 ft)/d. Although not directly compared in any study, each intervention appeared to have similar efficacy.
Adverse effects were not consistently examined in these trials. However, weaning from dexamethasone was associated with an increased risk of depression, and acetazolamide administration was associated with an increased incidence of polyuria and paresthesia.
Nifedipine administration prevented pulmonary edema in one small study, while in another it was not superior to placebo in prevention of AMS. Spironolactaone prevented nausea in one study, but was ineffective in preventing symptoms of AMS in two others.
Comment by Stan Deresinski, MD, FACP
Altitude related illness forms a continuum: from AMS, through pulmonary edema, and to cerebral edema. Although still poorly understood, each of these is believed to be the result of the body’s response to the hypoxemia caused by breathing oxygen at reduced partial pressure.
AMS may be defined as the presence, after a recent ascent, of headache together with one or more of the following: nausea or vomiting, gastrointestinal upset, fatigue, dizziness, or insomnia. AMS is reported to occur in approximately one-fourth of adults ascending to 2500 m (8200 ft), and approximately three-fourths ascending to 4500 m (14,800 ft).1 Of particular importance is the sleep altitude, presumably because of the associated reduced ventilatory drive. AMS generally resolves within a week at the destination altitude.
A number of nonpharmacologic measures may help prevent AMS. These include limiting ascent to approximately 300 m (984 ft) per day, staying for a day or two at intermediate altitudes and spending an extra night for every 600-900 m ascent, and avoidance of alcohol, sedatives, and hypnotics.
Most of these warnings are of little value for travelers arriving by airplane. Thus, the person who flies from the ocean port of Lima to Cuzco, Peru, on the way to visiting Machu Picchu, will have ascended approximately 5435 m (17,830 ft) in only one hour! Closer to home, individuals who take the drive and tram from Colorado Springs, Colo., to the top of Pike’s Peak will have rapidly ascended from approximately 1823 m to 4301 m (see Table).
| Table: Some High-Altitude Destinations | ||
| Destination | Altitude (m) | Altitude (ft) |
| Colorado Springs, Colo. | 1823 | 5980 |
| Mexico City | 2300 | 7456 |
| Thimphu, Bhutan | 2347 | 7700 |
| Sucre, Bolivia | 2600 | 8530 |
| Bogota, Colombia | 2610 | 8653 |
| Quito, Ecuador | 2835 | 9300 |
| Lhasa, Tibet | 3606 | 11,830 |
| La Paz, Bolivia | 3658 | 12,001 |
| Lake Titicaca | 3810 | 12,500 |
| Pike’s Peak, Colo. | 4301 | 14,110 |
| Cuzco, Peru | 5435 | 17,830 |
|
Mt. Kilamanjaro, Tanzania (Uhuru Peak) |
5894 | 19,337 |
This analysis by Dumont et al indicates that both acetazolamide and dexamethasone are effective in the prevention of AMS with ascent to higher than 4000 m at a rate of more than 500 m/d. Both drugs are also reasonably well tolerated, although there is a danger of depression after withdrawal of dexamethasone. The recommended dose of the former is 250 mg t.i.d., while that of the synthetic corticosteroid is 2 mg q.i.d. or 4 mg b.i.d. Nifedipine may prevent high-altitude pulmonary edema, but has not been demonstrated to prevent AMS. Thus, acetazolamide is the choice of most emporiatric specialists and dexamethasone is recommended only for individuals for whom acetazolamide is contraindicated (i.e., those with sulfa allergy).
Reference
1. Kozarsky P. Infect Dis Clin North Am 1998;12:305-324.
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