[Estimation of arterial oxygen saturation in relation to altitude]

Arterial Oxygen Saturation (AOS) predicts altitude sickness.

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.

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.

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.

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