Clinician's corner: What do we know about safe ascent rates at high altitude?

Although pharmacologic strategies are available for decreasing the risk of acute altitude illness, the best means of preventing these problems remains undertaking an adequately slow ascent. Guidelines regarding appropriate ascent rates have been published in various forums, and while these guidelines are generally similar to each other in regards to the recommended ascent rates and use of rest days, there is actually little evidence in the literature supporting the particular recommendations. The purpose of this review is to consider these guidelines and the issue of ascent rates in greater detail. Following a discussion of the evidence regarding ascent rates and acclimatization, the review considers several unanswered questions regarding the current guidelines, including the applicability of the guidelines for all altitude travelers, how best to determine the ascent rate, how to implement rest days, and whether pre-acclimatization strategies can be used to facilitate faster than recommended ascents. Given the current state of evidence, there is no reason to alter the current guidelines, as they likely work for the substantial majority of high altitude travelers. It is individuals traveling to high altitude for the first time for whom they remain most important, while those individuals with substantial prior experience at high altitude may opt for faster or slower ascent rates based on their prior experience. Rest days should remain a part of any ascent profile and should be used following any large gains in elevation rather than simply at specified time intervals. Pre-acclimatization strategies may decrease the risk of acute altitude illness but there is insufficient evidence to suggest they can be used to facilitate faster than recommended ascents. Further research may allow changes in practice in the future but for the time being, adherence to the current recommendations is the prudent approach for the majority of high altitude travelers.