Ep 159: A 30-Year-Old at High Altitude

This episode discusses the diagnosis and treatment of acute mountain sickness.

Read more on this topic in Harrison's.

Harrison's Principles of Internal Medicine, 22nd Edition

Transcript

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[Ms. Heidhausen] This is Katerina Heidhausen, executive editor of Harrison's Principles of Internal Medicine. Harrison's Podclass is brought to you by McGraw Hill's AccessMedicine, the online medical resource that delivers the latest content from the best minds in medicine. And now, on to the episode. 

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[Dr. Handy] Hi, everyone. Welcome back to Harrison's Podclass. We're your co-hosts. I'm Dr. Cathy Handy. 

[Dr. Wiener] And I'm Dr. Charlie Wiener, and we're joining you from the Johns Hopkins School of Medicine. 

[Dr. Handy] Welcome to today's episode: a 30-year-old at high altitude. 

[Dr. Wiener] Cathy, you'll recall, in a prior episode, we discussed high-altitude pulmonary edema during a hiking trip to Mount Kilimanjaro. Today, we're going to continue discussing altitude as more and more people are taking adventure tours. 

[Dr. Handy] All right, tell me about today's patient. 

[Dr. Wiener] So today's patient is a healthy 30-year-old woman who's always wanted to see Machu Picchu in Peru. She's planning to meet some friends in Quito, then go to Cusco and hike down to Machu Picchu. Unfortunately, her flight from Baltimore to Quito gets canceled, and she has to reschedule. She winds up flying directly to Cusco to meet her friends. 

[Dr. Handy] All right, before we start, let's just get some groundwork. Quito, the capital of Ecuador, has an altitude of about 9,000 feet, so that's pretty high. Cusco is even higher at about 11,000 feet. And interestingly, Machu Picchu is not a climb from Cusco but is a descent to 8,000 feet. These are all altitudes that travelers should be aware of and plan for in their travels. 

[Dr. Wiener] Exactly. So our patient arrives in Cusco in the late afternoon and joins her friends for dinner. Early that evening, she starts feeling headaches, nausea, fatigue, and dizziness. She tries to sleep, but she can't. One of her friends, who's a physician, finds no physical findings, including clear lungs. 

[Dr. Handy] I think she may have acute mountain sickness. Those are typical symptoms, and the lack of physical findings is also consistent. 

[Dr. Wiener] Tell me more about acute mountain sickness. 

[Dr. Handy] Well, as I said, acute mountain sickness, or AMS, is a symptomatic diagnosis with no physical findings. It must be distinguished from exhaustion or dehydration, hypothermia, an alcoholic hangover, and hyponatremia. It's thought to represent the opposite ends of a continuum of altitude-related neurologic disorders, with high-altitude cerebral edema, or HACE, being the most severe. HACE is an encephalopathy whose hallmarks are ataxia and altered consciousness with diffuse cerebral involvement, but generally without focal neurologic deficits. 

[Dr. Wiener] What are the risk factors for acute mountain sickness and other altitude illnesses? 

[Dr. Handy] Well, the trigger seems to be hypobaric hypoxia; however, the exact mechanisms underlying acute mountain sickness and HACE are unknown. The most important risk factors for the development of altitude illness are the rate of ascent and a prior history of high-altitude illness. So if you take a long time to get to elevation, you're less likely to develop AMS, but if you, let's say, fly to a high elevation and get there quickly, you're more likely. 

[Dr. Wiener] Are there any other risk factors or differences in epidemiology? 

[Dr. Handy] Exerting oneself at high altitude is a risk factor, but lack of physical fitness doesn't seem to have an impact. 

[Dr. Wiener] What about age? Age always seems to be a risk factor. 

[Dr. Handy] Children and adults seem to be equally affected, but people over 50 years of age may be less likely to develop AMS than younger people. In general, there's no gender difference in AMS incidence. 

[Dr. Wiener] Wow, that's the first time I hear that age is an advantage. Sleep disturbances are common, too. Right? 

[Dr. Handy] Sleep disturbances are among the most common adverse reactions to high altitude. Sleep desaturation, a common phenomenon at high altitude, is associated with AMS. A prospective study involving trekkers and climbers who ascended to altitudes above 13,000 feet found that high oxygen desaturation and low ventilatory response to hypoxia during exercise are both independent predictors of severe altitude illness. 

[Dr. Wiener] Good, and that brings us to our question. The question today asks, all of the following interventions are useful to decrease the risk of acute mountain sickness, except? Option A. is acetazolamide; option B. is dexamethasone; option C. is ginkgo biloba; D. gradual ascent; or E. proper hydration. 

[Dr. Handy] Gradual ascent, option D. with adequate time for acclimatization is the best method for the prevention of altitude illness. Even though there may be individual variation in the rate of acclimatization, a conservative approach would be a graded ascent of about 1,000 feet from the previous day's sleeping altitude above 10,000 feet. And then taking every third day of gain in sleeping altitude as an extra day for acclimatization is helpful. Spending one night at an intermediate altitude before proceeding to a higher altitude may enhance acclimatization and attenuate the risk of AMS. But frankly, few people, particularly tourists, take this graded approach. 

[Dr. Wiener] Option E. mentions hydration. That sounds like a good idea since you had mentioned that dehydration can cause AMS symptoms. 

[Dr. Handy] Yeah, proper hydration, but not overhydration in high-altitude trekking and climbing is aimed at countering fluid loss due to hyperventilation and sweating. And that may play a role in avoiding AMS. 

[Dr. Wiener] The others are medical approaches to prevention. 

[Dr. Handy] Yeah, and the next best is option A. acetazolamide. It can be administered at a dose of 125 milligrams twice a day for one day before ascent and then continued for about three days at the same altitude. It's the drug of choice for acute mountain sickness prevention. Acetazolamide inhibits renal carbonic anhydrase, causing prompt bicarbonate diuresis that leads to metabolic acidosis and hyperventilation. A meta-analysis limited to randomized controlled trials revealed that acetazolamide was effective in the prevention of AMS with a relative risk reduction of about 48% from values obtained with placebo. 

[Dr. Wiener] What about the others? 

[Dr. Handy] Dexamethasone, 8 milligrams per day in divided doses, is also effective. And in randomized studies, ibuprofen 600 milligrams three times daily has been shown to be beneficial in the prevention of acute mountain sickness. More recently, acetaminophen, one gram three times daily, was compared to ibuprofen, and it was as effective in a randomized double-blind study. However, more definitive studies need to be conducted before these drugs can be routinely recommended for AMS prevention. 

[Dr. Wiener] So I guess the ginkgo is not effective. So the answer is C? 

[Dr. Handy] Yes, a large-scale, randomized, double-blind, placebo-controlled trial in partially acclimatized trekkers clearly showed that ginkgo biloba is not effective in the prevention of AMS. 

[Dr. Wiener] Great. So the teaching points in this case are that acute mountain sickness, or AMS, is the mildest form of high-altitude neurologic disorders, with high-altitude cerebral edema being the worst. AMS is characterized by non-specific findings such as headache, nausea, and sleep disturbance. It is best prevented by gradual ascent to altitude, but the risk can also be decreased with medications such as acetazolamide. 

[Dr. Handy] And you can find this question and other questions like it in the Harrison's Self-Review, and you can learn more about this topic on the chapter on altitude illness. Visit the show notes for links to helpful resources, including related chapters and review questions from Harrison's, available exclusively on AccessMedicine. If you enjoyed this episode, please leave us a review, so we can reach more listeners just like you. Thanks so much for listening. 

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