The correct measurement of oxygen saturation at high altitude

Abstract

Background: Compared to measurements at sea level, measurement of oxygen saturation by pulse oximetry (SpO₂) at altitude differs fundamentally because of the cyclical course of SpO₂, caused by periodic breathing. Therefore, the determination of a representative SpO₂ value is difficult. In the literature, recommendations for a standardized measurement procedure are missing; different studies measure SpO₂ in different ways.

Key question: Does the visually determined SpO₂ 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 SpO₂ 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 SpO₂ 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 SpO₂-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.

Keywords: AMS; Acclimatization; High altitude; High altitude illness; Oxygen saturation; Pulse oximetry.