Bloch, Konrad E., Tsogyal D. Latshang, and Silvia Ulrich. Patients with obstructive sleep apnea at altitude. High Alt Med Biol 16:110-116, 2015.--Obstructive sleep apnea (OSA) is highly prevalent in the general population, in particular in men and women of older age. In OSA patients sleeping near sea level, the apneas/hypopneas associated with intermittent hypoxemia are predominantly due to upper airway collapse. When OSA patients stay at altitudes above 1600 m, corresponding to that of many tourist destinations, hypobaric hypoxia promotes frequent central apneas in addition to obstructive events, resulting in combined intermittent and sustained hypoxia. This induces strong sympathetic activation with elevated heart rate, cardiac arrhythmia, and systemic hypertension. There are concerns that these changes expose susceptible OSA patients, in particular those with advanced age and co-morbidities, to an excessive risk of cardiovascular and other adverse events during a stay at altitude. Based on data from randomized trials, it seems advisable for OSA patients to use continuous positive airway pressure treatment with computer controlled mask pressure adjustment (autoCPAP) in combination with acetazolamide during an altitude sojourn. If CPAP therapy is not feasible, acetazolamide alone is better than no treatment at all, as it improves oxygenation and sleep apnea and prevents excessive blood pressure rises of OSA patients at altitude.