The correct measurement of oxygen saturation at high altitude.

Background: Compared to measurements at sea level, measurement of oxygen saturation by pulse oximetry (SpO) at altitude differs fundamentally because of the cyclical course of SpO, caused by periodic breathing. Therefore, the determination of a representative SpO value is difficult. In the literature, recommendations for a standardized measurement procedure are missing; different studies measure SpO in different ways.

Key Question: Does the visually determined SpO 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) according to their individual observation. The used pulse oximeter saved the value for SpO every 4 s. Based on this, the calculated mean (SpO) was compared to SpO 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 differs only marginally (- 0.4%-points; ± 0.8) compared to SpO.

Conclusions: The correct pulse oximetric determination of SpO 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-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.