Pulse oximetry at high altitude.

Pulse oximetry is a valuable, noninvasive, diagnostic tool for the evaluation of ill individuals at high altitude and is also being increasingly used to monitor the well-being of individuals traveling on high altitude expeditions. Although the devices are simple to use, data output may be inaccurate or hard to interpret in certain situations, which could lead to inappropriate clinical decisions. The purpose of this review is to consider such issues in greater detail. After examining the operating principles of pulse oximetry, we describe the available devices and the potential uses of oximetry at high altitude. We then consider the pitfalls of pulse oximetry in this environment and provide recommendations about how to deal with these issues. Device users should recognize that oxygen saturation changes rapidly in response to small changes in oxygen tensions at high altitude and that device accuracy declines with arterial oxygen saturations of less than 80%. The normal oxygen saturation at a given elevation may not be known with certainty and should be viewed as a range of values, rather than a specific number. For these reasons, clinical decisions should not be based on small differences in saturation over time or among individuals. Effort should also be made to minimize factors that cause measurement errors, including cold extremities, excess ambient light, and ill-fitting oximeter probes. Attention to these and other issues will help the users of these devices to apply them in appropriate situations and to minimize erroneous clinical decisions.