Respiratory rate within the first hour of ascent predicts subsequent acute mountain sickness severity.

BACKGROUND Altitude illness results from hypobaric hypoxia at altitudes higher than 2500 meters above sea level. To determine whether vital signs can be used as predictors for severe acute mountain sickness, we carried out a prospective observational study. METHODS A cohort of 90 individuals (male/female ratio: 2; age: 13 - 65 years) in a mountain hotel's clinic at 3450 meters in Iran were studied from September through October 2006. Demographics and vital signs were measured during the first hour of ascent. The individuals were followed for acute mountain sickness symptoms including headache, dizziness, nausea or vomiting, insomnia, and fatigue. Lake Louise criteria were used to diagnose acute mountain sickness. Severe acute mountain sickness was considered if a score of equal or more than 5 was present. Significance was assigned to values of P<0.05. RESULTS Acute mountain sickness was diagnosed in 34 (37.8%) participants after 24 hours of ascent. Severe acute mountain sickness was detected in 14 (15.6%) participants. A respiratory rate of 20 or more during the first hour of ascent was recorded for nine (64.3%) patients with severe acute mountain sickness and 15 (19.7%) individuals in the negative/mild acute mountain sickness group. This suggests an association between early high respiratory rates and risk of subsequent severe acute mountain sickness (P=0.001). CONCLUSION There is an association between a rise in the respiratory rate and susceptibility to acute mountain sickness. This can enable us to predict severe acute mountain sickness and prevent it. Furthermore, Tochal Mountain Hotel guests should be aware of the risk of acute mountain sickness and should be recommended to use prophylactic acetazolamide or dexamethasone before ascent.