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.

Tarp Pitch: The Cave

I’ve mentioned this pitch in a couple of other posts, but it deserves its own. This is the tarp pitch I use most often. The video below doesn’t name it and it isn’t listed in David Macpherson’s encyclopedic collection of tarp pitches, so I call it “The Cave”.

I learned the pitch from this YouTube video about pitching an 8×10 Etowah tarp. The video is short and clear, less than two minutes, and it is much better than reading a description. Watch carefully, you do not stake the rear corners. You stake midway between the center and the corners.

I don’t pitch it self-standing like the video, instead I use a front guy line and throw a clove hitch around the top of my trekking pole. Still, it is easy for a single person to set up. My tarp is an Integral Designs Siltarp 2, an 8×10 tarp. In bad weather, a 10×10 tarp would provide a deeper cave and more coverage. Or you could pitch a poncho over the open end.

Here it is, set up at Jay Trail Camp in Big Basin State Park, when my son and I were hiking Skyline to the Sea. As you can see, there is a decent amount of room inside, though I wouldn’t call it spacious for two.


Here, my son is using a trekking pole to raise the ridge line. That would work if you had a Tundra Tarp with their quad-loop pole grabber, but it didn’t work for us. The pole just wouldn’t stay put. Besides, it was in the way. I recommend an external guy line from the center pull-out with a trekking pole to get some height—there is photo of that later.


And here I am the next morning. I’m 6’3″, so you can get a feel for the coverage. Not enough to keep rain from blowing in the front, but it sure keeps the breezes under control.


At Bonnie Lake in the Hoover Wilderness, we camped in a windy, exposed site. This was pitched cross-wise to the wind (I liked the view). It got down to 34º and there was a stiff breeze all night. If you look carefully in the photo or click through to the big version, you can see that I’ve set up my other trekking pole beind the pitch to pull the center tie-out up and make more room. Extra credit for spotting the bear bag.


At Lower Paiute Meadows later in the same trip, I found a sheltered spot with a nice tall branch on the downed tree for the back pull-up line.


Give this a try, it is easy to pitch single-handed once you get the hang of it. You can even pitch it in the wind, because the tarp is staked securely to the ground before you raise the pole.

Tarp Pitch: A-Frame

OK, everyone knows about this pitch, but there are some variations.

When you pitch it high and wide, it is the most room you can get for one pound of shelter.


You can pitch it almost down to the ground for more protection. If you do that, side tie-outs make a lot of extra room. My tarp doesn’t have sewn-in tie-outs, so I use Sierra Designs Grip Clips.


Finally, when the wind picks up, you can pitch it low and crawl inside your bunker for the night.