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Arterial oxygen saturation for prediction of acute mountain sickness.

BACKGROUND
Acute mountain sickness (AMS) is a usually self-limiting syndrome encompassing headache, nausea and dizziness. AMS is seen in those that go from low to high altitudes too quickly, without allowing sufficient time to acclimatize. At present, susceptibility to AMS cannot be predicted. One feature of AMS noted in some studies is impaired gas exchange. If impaired gas exchange presages AMS then those individuals with exaggerated hypoxemia at high altitude may be more likely to develop AMS. If true, then monitoring of arterial oxygen saturation (SaO2%) may differentiate AMS-resistant individuals from those with impending AMS.


METHODS
To test this hypothesis, we measured SaO2% and AMS symptom scores in 102 healthy asymptomatic climbers at 4200 m on Denali (Mt. McKinley) prior to their further ascent toward the summit at 6194 m, and on their return from higher altitudes to 4200 m.


RESULTS
The results show that exaggerated hypoxemia in asymptomatic climbers prior to further ascent correlates with subsequent AMS (r = -0.48, p < 0.001). Criteria are presented for identification of 80-100% of those climbers who later become ill with AMS.


CONCLUSION
We conclude that resting arterial hypoxemia is related to later development of clinical AMS, and can exclude the occurrence and caution those at risk for development of subsequent AMS. Likely mechanisms are hypoventilation relative to normally acclimatizing individuals and/or abnormalities of gas exchange. Thus, non-invasive oximetry provides a simple, specific indicator of inadequate acclimatization to high altitudes and impending AMS.