Acute mountain sickness and acetazolamide. Clinical efficacy and effect on ventilation

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Abstract
Climbers (64) participated in a randomized clinical trial of acetazolamide [a carbonic anhydrase inhibitor] prophylaxis for acute mountain sickness (AMS) during rapid, active ascent of Mt. Rainier [Washington, USA]. Twenty-nine (93.6%) of 31 climbers receiving acetazolamide and 25 (75.8%) of 33 receiving placebo attained the summit. Time spent ascending from sea level to the summit (4394 m) averaged 33.5 (23-48 h). On the summit AMS was less common in climbers receiving acetazolamide, and they experienced less headache, nausea, drowsiness, shortness of breath, and dizziness and a greater sense of satisfaction and psychological well-being. Minute ventilation on the summit was significantly greater in subjects taking acetazolamide (24.9 .+-. 2.0 l/min vs. 16.9 .+-. 3.8 l/min). Expired vital capacity was greater on the summit in the acetazolamide group (6.9 .+-. 0.4 l vs. 5.8 .+-. 0.4 l). Evidently, acetazolamide is effective in the prophylaxis of AMS for climbers attempting rapid, active ascent. Increased ventilation at altitude, producing an increased alveolar O2 tension, may be related to the observed amelioration of symptoms.