14 March 2014

Acute High-Altitude Illness / Acute Mountain Sickness (AMS) and mountain ultramarathon running


While I think it works perfectly fine to simulate the steep technical ascents and descents encountered in Alpine terrain on some of the trails on the local hills here in Uppsala it is of course impossible to simulate the high altitudes in the “real” mountains. Disturbingly, when I was skiing with my family in Courmayeur some weeks ago I got an annoying headache and felt a little nauseated the second day of skiing. The altitude was moderate around 2500 meters, but I could clearly identify the similar feeling as I had the second day of Tor des Géants (TDG) last year when I during the second stage started to have similar experience when going over an altitude of around the same altitude of 2500 meters. The second stage of TDG passes some of the highest passes, among them Col Loson at 3299 meters (10823 feet), and I really struggled over those without being able to get enough energy due to the nausea. I felt much better already on the descent to the second life-base to Cogne and even though I was afraid for the rest of the race that the feeling would return at some of the high passes later in the race I did not experience the same thing and seemed to have been acclimatized to the height. The same thing was repeated when skiing in Courmayeur as I did not feel anything on the third day and onwards.

Col Loson at 3299 meters (10823 feet)

Looking into the rather extensive literature on Acute High-Altitude Illness / Acute Mountain Sickness (AMS) it is clear that my symptoms of headache plus nausea and fatigue clearly could be attributed to this. Some of the good recent reviews on the subject is “Acute high-altitude illnesses” by Bärtsch and Swenson in New England Journal of Medicine (NEJM) 2013; 368: 2294-2302, “Wilderness medical society consensus guidelines for the prevention and treatment of acute altitude illness” by Luks et al in Wilderness & Environmental Medicine 2010; 21: 146-155 and “Altitude illness: update on prevention and treatment” by Eide and Asplund in Current Sports Medicine Reports 2012; 11: 124-130 and "Acute Altitude Illness" by Imre et al in BMJ 2011; 343: d4943 . The figure below is from Bärtsch and Swenson’s article in NEJM and outlines the symptoms and signs of AMS and those of the more severe disorders High-Altitude Cerebral Edema (HACE) and High-Altitude Pulmonary Edema (HAPE).  There is a risk of progression of AMS into the more rare life-threatening HACE and HAPE, even though the correlation is not perfect.

Figure from Bärtsch & Swenson NEJM 2013; 368: 2294

Acute Mountain Illness (AMS) is surprisingly common with an incidence of about 25% of persons rapidly ascending to moderate altitudes of > 2500 meters. HACE and HAPE are much less common and typically only observed at higher altitudes. A good figure on the effects of various altitudes is from the Imray et al article 2011:

Figure from Imray et al 2011; 343: d4943

There was just a really interesting study published in Medicine Science Sports Exercise 2013; 45: 792–800 by  Beidleman and colleagues entitled “Predictive models of acute mountain sickness after rapid ascent to various altitudes”. In this study they have looked at previously published data and created a risk model for predicting the probability and severity of AMS after rapid ascent to altitudes of 2000 to 4500 meters. In the first figure below from their article the lowest group of lines start at 2000 meters and and increases by 500 m until reaching 4500 m for the top group of lines. Panels A and B demonstrate the effect of activity on probability of AMS in high active versus low active men and high active versus low active women. Panels C and D demonstrate the effect of sex on probability of AMS in high active men versus high active women and low active men versus low active women. The next figure demonstrates the probability of mild, moderate, and severe AMS going from 2000 to 4500 m in high active men, low active men, high active women, and low active women. One of the most pronounced risk factors is if you previously have experienced AMS.
 
From Beidleman et al Med Sci Sport Exerc 2013; 45: 792
 
From Beidleman et al Med Sci Sport Exerc 2013; 45: 792

I have tried to find incidence figures of AMS for mountain ultramarathons, like UTMB, Hardrock 100 or TDG, at high altitudes without finding any studies. As the ascent to at least moderately high altitudes in these races indeed is very rapid, and many runner’s start without long acclimatization as is the standard for alpine climbing expeditions, I expect there are many runners like myself who have experienced AMS. Reading race reports from races you also get the picture that at least in some instances AMS can lead to early drop-outs. I think what many runners refer to as “nutritional problems” or similar might actually be AMS.

What could you then do to avoid AMS when running a mountain ultramarathon at high altitudes? There are some evidence-based recommendations with regards to pharmacological interventions that could be taken to prevent AMS. To prevent AMS and HACE Acetazolamide or Dexomethasone are recommended. However, I would be cautious of both drugs as they are really not ideal for ultramarathons – for instance Acetazolamide can increase the risk of hyponatremia, another major risk when running ultramarathons. To prevent HAPE Nifedipine is recommended, but as HAPE is much less common and so severe I think you should not run mountain a ultramarathon at high altitudes if you are at risk and have experienced this before, at least not before consulting the medical director of the race. So what could you then do to prevent AMS? Slow ascent of 300–500 m/day above 2500–3000 m as recommended for mountain climbing is clearly out of the question. What is left is acclimatization at altitudes above 2500 meters before the race and this is what I will opt for when running PTL this August. Looking at my personal onset of symptoms of AMS after around 12-24 hours I think a short acclimatization of one or two days when I go on day hikes at above 3000-3500 meters will be enough.

If you develop AMS usually non-steroid anti-inflammatory drugs (NSAIDs), such as diclofenac or ibuprofen, are recommended for the headache and anti-emetics for the nausea. However, NSAIDs are clearly not recommended for mountain ultramarathon running as there are other risks with those and I think it also too risky to try to suppress the symptoms of AMS during a race as it would be very important to early in the process detect possible progression to HACE, which would require immediate descent and interruption of the race.

In summary, I think I really could have saved time during TDG if I had been better acclimatized to the altitude and avoided, or at least had less severe, AMS during the second day. Looking at my speed and position during the race I lost a lot of time during the second day when my legs still were really fresh and I had not yet become sleep deprived as later in the race.


Analysis of my peformance at TDG 2013

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