Abstract
Purpose: A decision tree based on a clinico-physiological score (SHAI score) has been developed to detect subjects susceptible to Severe High Altitude Illness (SHAI). We aimed to validate this decision tree, to rationalize the prescription of acetazolamide (ACZ) and to specify the rule for a progressive acclimatization.Methods: Data were obtained from 641 subjects in 15 European medical centers before and during a sojourn at high altitude. Depending on the value of SHAI score, advice was given and ACZ was eventually prescribed. The outcome was the occurrence of SHAI at high altitude as a function of SHAI score, ACZ prescription and use and fulfillment of the acclimatization rule.Results: The occurrence of SHAI was 22.6%, similar to what was observed 18 years before (23.7%), while life-threatening forms of SHAI (High Altitude Pulmonary and Cerebral Edema) were less frequent (2.6% to 0.8%, P=0.007). The negative predictive value of the decision tree based was 81%, suggesting that the procedure is efficient to detect subjects who will not suffer from SHAI, therefore limiting the use of ACZ. The maximal daily altitude gain that limits the occurrence of SHAI was established at 400 m. The occurrence of SHAI was reduced from 27% to 12% when the recommendations for ACZ use and 400 m daily altitude gain were respected (P<0.001).Conclusion: This multicenter study confirmed the interest of the SHAI score in predicting the individual risk for SHAI. The conditions for an optimized acclimatization (400 m-rule) were also specified and we proposed a rational decision tree for the prescription of acetazolamide, adapted to each individual tolerance to hypoxia