Effect of Moderate Elevation above Sea Level on Blood Oxygen Saturation in Healthy Young Adults

BACKGROUND: Arterial hemoglobin oxygen saturation (SaO₂) decreases at an altitude of >1,500 m. There are no reports on normal SaO₂ at altitudes between 0 and 1,500 m. The clinical significance of decreased SaO₂ at such altitudes is unclear. OBJECTIVE: To test the hypothesis that in healthy volunteers normal SaO₂ at moderate altitude (MA; 725 m) is lower than that at almost sea level (SL; 43 m). METHODS: SaO₂ was measured by transcutaneous pulse oximetry in young healthy volunteers at MA and was compared to equivalent measurements at SL. In addition, a 6-min walk test was performed and SaO₂ at the end of the walk was compared between the two locations. RESULTS: 111 males were checked at MA and 101 at SL. At rest, nadir SaO₂ was 95% at MA compared to 97% at SL. Mean SaO₂ at rest was slightly higher at SL (98.53 ± 0.52) compared to MA (98.11 ± 0.8; p < 0.01). In subjects who completed the 6-min walk test, SaO₂ slightly decreased after the test in both locations, by 0.38 ± 0.65% in the SL group and by 0.37 ± 1.12% in the MA group. This difference is not statistically significant by univariate analysis; however, a multiple regression analysis indicated that the drop in SaO₂ was higher at MA than at low altitude. CONCLUSIONS: We found a low but significant difference in SaO₂ between near-SL and at an altitude of 725 m. The clinical significance of this difference, in terms of human health, is probably minimal.