Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.See all posts »
Pulse Oximetry and Predicting Acute Mountain Sickness
In the most recent issue of Wilderness & Environmental Medicine appear two articles on a similar topic. The first is an article by Dr. Dale Wagner and colleagues, entitled “Oximetry Fails to Predict Acute Mountain Sickness or Summit Success During a Rapid Ascent to 5640 Meters” (WEM 2012;23:114). The second is an article by Dr. Hang-Cheng Chen and colleagues, entitled “Change in Oxygen Saturation Does Not Predict Acute Mountain Sickness on Jade Mountain” (WEM 2012;23:122). Both studies confirmed what has been noted before, namely, that arterial oxygen saturation, or SaO2, (in these cases as measured by a transcutaneous pulse oximeter) does not predict which individuals will develop acute mountain sickness (AMS). On a recent trip to Everest Base Camp, there were more than a few portable battery-powered pulse oximeters in the hands of the doctors, and everyone took delight in measuring his or her SaO2 and reporting back to the group the number and how they were feeling. Everyone also noticed how variable were the measurements, depending on state of hydration, fatigue, fingertip temperature, and breathing rate. It was not uncommon to be able to slightly manipulate the value simply by cooling or warming one’s hands.
It would be nice to have something as simple as a single SaO2 measurement upon which to base a prediction for who will develop AMS. Unfortunately, such a predictor doesn’t yet exist. We are fairly confident of contributing factors – rapid ascent, altered breathing during sleep, dehydration, overexertion, and so forth – to developing AMS, but there isn’t a blood test, urine sample, or other “quick read” determination upon which we can rely with assurance. It makes sense that a person with a low SaO2 might be at increased risk for developing a high-altitude related illness, so it is also logical to keep a close watch on someone who has a deteriorating value.
So, perhaps the trend is somehow predictive. However, while a low reading may be a disqualifier for further ascent or guide administration of oxygen in a person who is symptomatic from lack of that precious gas, an isolated single reading at sea level or at any other predetermined elevation above sea level cannot be considered a predictor of who is going to get into trouble.
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