Back in 2021, I wrote about the case of Daniel Granberg, a 24-year-old from Colorado who died at the summit of a Bolivian mountain called Illimani of what turned out to be high-altitude pulmonary edema (HAPE). What was notable about the incident was that Illimani is only 21,122 feet above sea level, well below the notorious Death Zone, which starts around 26,000 feet and is where most climbing fatalities in the Himalaya occur. And Granberg hadn’t seemed notably distressed: the HAPE snuck up on him without obvious warning signs.
That’s a little scary for anyone venturing to these sorts of high-but-not-extreme altitudes. Ideally, you’d like to have a better sense of the risk factors and warning signs that signal the difference between run-on-the-hill acute mountain sickness and more severe forms of altitude illness like HAPE.
A new study in Wilderness & Environmental Medicine offers some useful clues. Emergency physicians from the University of Vermont and the medical staff at Aconcagua Provincial Park, led by Vermont’s Andrew Park, crunched the data on all climbers diagnosed with HAPE during the month of January in 2024 and compared their responses to climbers who didn’t get HAPE. Sure enough, there were some notable differences in how fast they climbed, how long they acclimatized to various stages of elevation, and what symptoms they displayed.
Aconcagua, in Argentina, is the highest mountain in Americas at 22,838 feet. It’s also the highest mountain outside Asia, and more significantly is perhaps the highest non-technical summit in the world, meaning that it’s possible to ascend without specialized climbing skills and equipment. That makes it accessible, but it also means that climbers can hurry up the mountain at a dangerous pace. A study back in 2013 found that roughly three climbers die each year out of more than 3,000 who attempt it. HAPE was the second-leading cause after trauma, accounting for a fifth of the deaths.
Park medical staff screen climbers at camps at roughly 11,000 feet and 14,000 feet. Crucially, there are no standard sleeping camps between those two elevations, which means you have to make that 3,000-foot jump in one night. Standard guidelines on altitude illness from the Wilderness Medical Society (which I wrote about in detail here) suggest increasing your sleeping elevation by no more than 1,500 feet per night once you’re above 10,000 feet. If logistics force you to make a bigger jump, you need to add rest days to keep the average rate of climbing below that threshold.
A total of 17 climbers were diagnosed with HAPE in January 2024. The key feature of HAPE is a potentially dangerous build-up of fluid in the lungs that interferes with the delivery of oxygen into the bloodstream. It’s mainly diagnosed on the basis of shortness of breath, lower than expected blood oxygen levels for a given altitude, and a crackling sound in the lungs. None of the HAPE victims died; all were quickly evacuated by helicopter to lower elevations, which is the main recommendation for treating HAPE.
Overall, the climbers diagnosed with HAPE were very similar to a group of 42 climbers surveyed during the same period who weren’t diagnosed with HAPE. But a few suggestive differences emerged. The most significant was the number of nights they spent at the 14,000-foot camp, after that 3,000-foot jump in sleeping elevation. The HAPE climbers spent an average of 3.6 nights at that camp, compared to 5.0 nights for the non-HAPE climbers, a statistically significant difference.
Interestingly, both groups had planned a total of 10.4 nights, on average, to reach the summit. The HAPE group actually spent slightly longer getting to 14,000 feet, but they spent less time adjusting to that elevation. Typically the risk of altitude illness starts ramping up beyond about 10,000 feet, so once you get to 14,000 feet you’re well into the zone where many people will be experiencing altitude-related symptoms.
On a related note, 71 percent of the HAPE patients reported that they had symptoms of acute mountain sickness (AMS) at 14,000 feet. AMS is the most common and mild form of altitude illness, typically manifesting as a headache plus other symptoms like nausea and lethargy. The typical advice for AMS is that you should stop ascending, and if symptoms don’t resolve within a few days, descend to a lower elevation. Notably, every single one of the climbers who had AMS at 14,000 feet then went on to develop HAPE (at a median elevation of 18,000 feet) reported that their AMS symptoms hadn’t resolved before they continued their ascent.
There are a few other observations that raise more questions than answers. Just under half the HAPE climbers reported taking acetazolamide, a diuretic known to climbers under the brand name Diamox that helps ward off AMS. In contrast, only a fifth of the non-HAPE climbers used it. It seems unlikely that Diamox is causing HAPE. Presumably climbers who were struggling to handle altitude were more likely to try Diamox and also more likely to eventually develop HAPE. Still, the researchers suggest that it’s an observation that’s worth following up on.
Similarly, 44 percent of the HAPE group reported having a recent upper respiratory tract infection, compared to just 29 percent of the non-HAPE group. This difference wasn’t statistically significant, but it’s plausible it might have been significant with a larger sample size. Lingering inflammation in the respiratory tract might contribute to the leaky capillaries associated with HAPE. For now, it’s another idea to check out in future research.
The strongest conclusions we can draw from the data are also the most familiar ones: ascend slowly, and if AMS strikes, pause your ascent until symptoms resolve. That’s easy advice to give, but hard to follow, especially because AMS symptoms like headache and fatigue are so vague and commonplace at high elevations. But the data here offers a stark warning: ignoring this advice heightens your risk of progressing to more serious forms of altitude illness that sometimes, with little warning, turn out to be fatal.
For more Sweat Science, join me on Threads and Facebook, sign up for the email newsletter, and check out my forthcoming book The Explorer’s Gene: Why We Seek Big Challenges, New Flavors, and the Blank Spots on the Map.
The post Why Climbers on Aconcagua Get Serious Altitude Illness appeared first on Outside Online.
