The correct measurement of oxygen saturation at high altitude

Background Compared to measurements at sea level, measurement of oxygen saturation by pulse oximetry (SpO 2 ) at altitude differs fundamentally because of the cyclical course of SpO 2 , caused by periodic breathing. Therefore, the determination of a representative SpO 2 value is difficult. In the literature, recommendations for a standardized measurement procedure are missing; different studies measure SpO 2 in different ways. Key question Does the visually determined SpO 2 value correlate with the actual average of the measurement interval? Methods Four participants of an expedition (6013 m; Pakistan), familiar with pulse oximetry at altitude, wrote down the representative value of the measurement interval of 3 min (SpO 2visual ) according to their individual observation. The used pulse oximeter saved the value for SpO 2 every 4 s. Based on this, the calculated mean (SpO 2memory ) was compared to SpO 2visual after finishing the expedition (128 measurements > 2500 m). Results The spread of the single values within the measurement interval is high (in single cases up to 17%-points) in case of insufficient acclimatization. With increasing acclimatization, the measured values stabilize. SpO 2visual differs only marginally (− 0.4%-points; ± 0.8) compared to SpO 2memory . Conclusions The correct pulse oximetric determination of SpO 2 at high altitude requires a standardized measurement procedure; the investigator is familiar and trained. Anyway, the measurements have to be done in the continuous mode of the pulse oximeter over a sufficient timeframe (3 SpO 2 -fluctuation cycles; 2–3 min). We recommend to record the maximum and the minimum value of the measurement interval and to use a pulse oximeter device with memory function.