Lowering the Risk of Acute Mountain Sickness (AMS)

The journal Wilderness & Environmental Medicine published an article in June with new evidence-based guidelines on acute mountain sickness (AMS), also known as altitude sickness, as well as HAPE and HACE. The article, Wilderness Medical Society Consensus Guidelines for the Prevention and Treatment of Acute Altitude Illness (also: the erratum, with a corrected risk table), is worth reading in full, but I’m going to pull out two highlights.

First, how to keep our risk low. The paper lists three risk categories: low, medium, and high. The description of the “low” category is a good rule for planning mountain trips. Note that the altitudes listed are sleeping altitudes. You can hike higher, but you need to sleep low.

  • Individuals with no prior history of altitude illness and ascending to ≤ 2800 m (9200 ft);
  • Individuals taking ≥ 2 days to arrive at 2500-3000 m with subsequent increases in sleeping elevation < 500 m/day and an extra day for acclimatization every 1000 m (arrive at ~8000-9000 feet, increases in elevation less than 1600 feet/day)

Some people are affected by AMS at 7000 feet, so don’t think you are risk-free by following these guidelines. There are other benefits to staying well under these limits. Slower climbing at the beginning of a trip can improve your performance later. At Philmont I was climbing Mt. Phillips (11,700 ft) stronger than I had climbed Emigrant Pass (9800 ft) the previous year. The difference? At Philmont, we took six days to get to Mt. Phillips instead of the three days we took to get to Emigrant Pass. The trailheads were at nearly the same altitude and we spent a night at the trailhead both times.

Monitor hydration carefully, because the symptoms of dehydration and AMS are very similar.

Second, how do we treat AMS? There is only one treatment that does not require extra equipment or medications, and that is “descend”. Luckily, it is also the only treatment given a grade of “1A” (strong recommendation, high-quality evidence).

The article also has a clear summary for diagnosing AMS, something you should print out and keep with that copy of the Lake Louise AMS Criteria that you already carry.

If you do have someone on your crew with a history of AMS, print out this article, with the erratum, and take it to your physician. There are established medications for AMS prevention.

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