The Challenges without O2 – Part II: Acute Mountain Sickness

I talked last time about the energy problem at the summit of Mt Everest. But this is just one aspect of the challenge – medically there is also a lot which can go wrong!

First there is the impact of low blood oxygen (hypoxia) on your brain. Unlike your muscles, the brain can only generate energy with oxygen – it can’t work anaerobically. In hypoxic conditions this inhibits the firing of neuron synapses, and thus impairs your cognitive functions. I remember watching a video of someone at 8,000m (26,000ft) taking 10 minutes just to put on his shirt! Disorientation, poor judgment and loss of consciousness are serious risks in a place where rescue is essentially impossible.

Altitudes above about 3,000m (10,000ft) can also cause other medical problems, collectively called Acute Mountain Sickness (AMS).  Some of the milder conditions are a miserable inconvenience, such as headache, nausea or insomnia. There are also a number of more serious conditions to worry about.

Hypoxia causes a rise in blood pressure as your body rapidly pumps blood made much thicker than normal by all the extra red blood cells you create to carry oxygen. Simultaneously your veins automatically constrict which compounds the problem. If the pressure increases too much it can cause plasma to be squeezed out of your blood vessels and into the surrounding tissue. If that tissue is your lungs it causes a pulmonary edema (known as HAPE), and you literally drown as your lungs fill up with fluid from the inside. No joke that. If the tissue is your brain it causes a cerebral edema (known as HACE), a swelling of the brain which can result in coma and death. Also no joke.

Mitigating the risks of developing these conditions is a primary goal of acclimatization. Some people are more susceptible than others, but these conditions can still happen to anyone, from amateur climber to experienced Sherpa. So far I’ve been fortunate to never suffer any AMS symptoms, which is a good sign, but at extreme altitude the risks are never 0%.

The emergency treatment for these conditions is rapid descent, which is not always easy. Fortunately there are two drugs, nifedipine and dexamethasone, which have been proven to temporarily mitigate some of the early impacts of HAPE and HACE, hopefully giving you enough additional time to safely descend. Standard practice is to carry these on summit day, which I will do.

This is one time I’m happy not to have a photo of a past experience to share! So here is a photo of me at 6,000m (20,000ft) on Aconcagua in Argentina, stuck in a tent during a storm and looking like I have AMS…



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