[Arterial oxygen saturation during ascent of a mountain higher than 8,000 meters]

Arterial oxygen saturation (SaO2) diminishes with altitude.

To know the values of SaO2 in healthy mountaineers during the ascent of a mountain higher than 8,000 metres.

On occasion of an expedition to Gasher brum II (8,035 m), SaO2 at rest was measured by pulse oxymetry during the approach march, in the base camp (on day one and one month later), in camps II and III, during the assault at 7,500 m and on the summit.

During the approach march, the SaO2 in Paiju (3,365 m) was 92.9 +/- 1.4% and in Gore II (4,250 m) 85.0 +/- 4.3%. In the base camp (5,200 m) it was 78.4 +/- 9.5% on the first day and 87.4 +/- 3.0% one month later (p < 0.007). In camp II (6,500 m) it was 72.7 +/- 6.7%. In camp III (7,000 m) it was 68.0 +/- 9.3% (recorded on 21 asymptomatic climbers). At this altitude a SaO2 of 40% was recorded during sleep in an asymptomatic subject, apparently without apnoeic crises. During the assault at 7,500 m, SaO2 was 60.5 +/- 13.5% (measured on 4 climbers). On the summit (8,035 m) the SaO2 of two subjects was 84% and 88%, respectively.

During expeditions to mountains higher than 8,000 metres, mountaineers have extremely low values of SaO2, similar to those of patients with severe respiratory failure. SaO2 increases progressively with acclimatization. SaO2 on the summit could have been relatively high, probably because of hyperventilation.