[Estimation of arterial oxygen saturation in relation to altitude]

Abstract

Background and objectives: Arterial Oxygen Saturation (AOS) predicts altitude sickness.

Objectives: To estimate the AOS values with relation to altitude. Furthermore, make a graph to use during activity which assesses the AOS for each altitude and the normal range.

Patients and method: Values of AOS were assessed during eight high mountain activities in the Alps, Himalaya, Caucasus and Andes; 53 mountaineers participated, 17 of them in more than one activity; 761 measurements of AOS were registered.

Results: A Logistic Regression Model was made to estimate the AOS values dependent on altitude, adjusted to possible related factors. A strong lineal relationship exists between altitude and AOS (R²=.83, P<.001); .7 points more in women. The AOS in a particular altitude is not related to age, weight, height, smoking, heart rate, or even with previous experiences in mountains. The calculation of the AOS responds to the follow equation: Blood Oxygen Saturation=103.3-(altitude × .0047)+(Z), being Z=.7 in men and 1.4 in women. A scatter plot was made to relate the estimated altitude with the AOS, with their normal limits values: percentiles 2.5 and 97.5.

Conclusions: The simple calculation of the AOS estimated for a particular altitude with the proposed graphic can help in the early decision-making onsite.

Keywords: Altitude sickness; Arterial oxygen saturation; Mal de altura; Montañismo; Mountaineering; Pulse oximetry; Pulsioximetría; Saturación arterial de oxígeno.