Advice Ignored on Acute Mountain Sickness
Abstract and Commentary
By Brian G. Blackburn, MD and Michele Barry, MD FACP
Dr. Blackburn is a Clinical Assistant Professor in the Division of Infectious Diseases and Geographic Medicine at Stanford University School of Medicine. Dr. Barry is the Senior Associate Dean for Global Health at Stanford University School of Medicine.
Drs. Blackburn and Barry report no financial relationships to this field of study.
Synopsis: A retrospective survey of 744 Dutch and Belgian travelers who had ventured to 2,500 m. (8,200 ft.) or higher revealed that 25% developed acute mountain sickness (AMS). Only half of this group had followed pre-travel advice regarding altitude sickness, and few took preventative acetazolamide.
Source: Croughs M, et al. Acute mountain sickness in travelers who consulted a pre-travel clinic. J Travel Med 2011;18:337-43.
Acute mountain sickness (AMS) is a syndrome that can affect travelers who are not acclimatized and gain altitude too quickly, usually occurring above 2,500 m. (8,200 ft.) elevation. Typical symptoms include headache, nausea, dizziness, sleeplessness, anorexia, and fatigue. Although usually benign, life-threatening high altitude cerebral or pulmonary edema (HACE or HAPE) can result if the syndrome is allowed to progress. Pharmacologic treatment and prophylaxis (e.g., acetazolamide) are efficacious,1-3 but perhaps the most important preventative measure is halting ascent at the onset of any AMS symptoms. In addition, if symptoms worsen while travelers rest at the same altitude, they must descend. Pre-departure counseling regarding the symptoms and risks of AMS is critical for decreasing the risks of this potentially serious illness.
Consensus guidelines have been published regarding the prevention and treatment of altitude sickness.4,5 These suggest limiting daily ascent to a maximum of 500 m. (1,600 ft.) for activities above 2,750 m. (9,000 ft.), adding one acclimatization day for every 1,000 m. (3,300 ft.) elevation gained above this altitude, and initiating acetazolamide prophylaxis in certain specific situations4,5 The authors undertook a retrospective survey of adult travelers to high altitude that were seen at one of four travel clinics in the Netherlands and Belgium before their trip. These patients were given specific written and oral instructions about AMS during the visit, and written surveys regarding AMS were then mailed to all patients after their return.
Overall, 744 persons that slept >1 night above 2,500 m. (8,200 ft.) were included in the study. The age range was 17-76 (mean 36) years; most traveled to South America (74%) or Asia (18%). The maximum sleeping altitude averaged 3,950 m. (13,000 ft.). Above an altitude of 2,500 m. (8,200 ft.), 43% of people climbed greater than 500 m. (1,600 ft.) per day.
While 658 respondents (88%) read the information they received about AMS from the travel clinic, 160 (22%) did not understand instructions regarding the use of acetazolamide. Although 541 (72%) brought acetazolamide with them, only 116 (16%) took it for AMS prevention; the median dose among such users was 125 mg twice daily (median course four days). Sixty-six (9%) had suffered from AMS previously, and these individuals took acetazolamide prophylaxis twice as frequently as those who had never suffered from AMS (29% vs. 14%).
Overall, 184 respondents (25%) had symptoms during their trip that met the definition of AMS; 76% of these resolved within three days. Eighty-seven (47%) continued climbing despite their AMS symptoms, and one-quarter of these individuals experienced some exacerbation of their symptoms. One-hundred two (55%) symptomatic patients took acetazolamide for treatment of AMS (median 375 mg total daily dose for three days). Several travelers reported that they did not think their symptoms were severe enough to warrant acetazolamide, or that they were uncertain regarding when they should begin taking it.
Commentary
This retrospective survey of high altitude travelers who had received advice about AMS from travel clinics before their journey yielded interesting descriptive results. The overall rate of AMS for travelers to this altitude was generally similar to past studies, despite the advice given by the travel clinics.6,7 As has been demonstrated in other settings, predictors of AMS included a past history of AMS, a higher maximum altitude, and spending fewer nights acclimatizing. Younger age and female sex were demographic factors associated with a higher risk of AMS; past studies have been mixed on the relationship of these factors to the development of AMS.6,7
The troubling finding in this study was the strikingly low compliance rate of travelers with the advice they received about AMS. Despite care at travel clinics specifically geared towards addressing the risks of AMS, 43% of travelers climbed greater than 500 m. (1,600 ft.) per day when above 2,500 m. (8,200 ft.), and only 16% took acetazolamide for prophylaxis of AMS. Of even greater concern, almost half of patients with symptoms of AMS continued to climb. Although the ambitious, fixed itineraries trekkers and climbers frequently embark upon may mean that compliance with advice regarding AMS will always be problematic, improvement of counseling protocols might help alleviate this.
For example, advice might focus on the risks of developing HACE or HAPE if patients continue to ascend with symptoms of AMS, guidelines for the use of acetazolamide might be made clearer, and patients could be advised to build more flexibility into itineraries, so that travelers with AMS might be more likely to rest and acclimatize rather than continuing to ascend. Although the best means to achieve these goals remains uncertain, advice should probably be communicated both orally and in writing, in a standardized manner for all patients. If it seems that unsafe ascent remains likely in a particular patient despite such advice, recommendations regarding inclusion of at least one companion who is trained in the management of altitude sickness, and who would carry pharmacologic (e.g., dexamethasone) and non-pharmacologic (e.g., a Gamow bag for HACE or HAPE) therapy for AMS and its complications might also be considered.
A surprising finding of this study was the apparent ineffectiveness of acetazolamide prophylaxis. The median dose used (125 mg twice daily) was less than the previously recommended prophylaxis dose (250 mg twice daily), and earlier studies did suggest that higher doses were necessary to effectively prevent AMS.8 However, more recent randomized studies in multiple settings have demonstrated the efficacy of 125 mg twice daily for preventing AMS,1-3 and this is now the recommended dose in several consensus guidelines.4,5 While acetazolamide also appeared ineffective at alleviating symptoms of AMS in this study, the dose used (375 mg total daily dose) was lower than the currently recommended dose (250 mg twice daily) for AMS treatment. Use of acetazolamide for treatment of AMS was also erratic in this cohort, again resulting in selection bias.
While intriguing, the results of this study are insufficient to conclude that a change in the recommendations regarding acetazolamide use for AMS are necessary. The key contribution of this study is to increase awareness among travel medicine practitioners that their advice regarding AMS will not be followed by many high-altitude travelers, and that clinic practices may need to be adapted to this unfortunate reality of caring for such patients.
References
- Basnyat B, et al. Acetazolamide 125 mg BD is not significantly different from 375 mg BD in the prevention of acute mountain sickness: The prophylactic acetazolamide dosage comparison for efficacy (PACE) trial. High Alt Med Biol 2006; 7:17–27.
- Basnyat B, et al. Efficacy of low-dose acetazolamide (125 mg BID) for the prophylaxis of acute mountain sickness: A prospective, double-blind, randomized, placebo-controlled trial. High Alt Med Biol 2003; 4:45–52.
- van Patot MC, et al. Prophylactic low-dose acetazolamide reduces the incidence and severity of acute mountain sickness. High Alt Med Biol 2008; 9:289-93.
- Hackett PH, et al. Altitude Illness. In: Brunette GW, Kozarsky PE, Magill AJ, Shlim DR (eds). CDC Health Information for International Travel 2012. New York: Oxford University Press; 2012:60-65.
- Luks AM, et al. Wilderness Medical Society consensus guidelines for the prevention and treatment of acute altitude illness. Wilderness Environ Med 2010; 21:146–155.
- Hackett PH, et al. High-altitude illness. N Engl J Med 2001; 345:107-14.
- Basnyat B, et al. High-altitude illness. Lancet 2003; 361:1967–74.
- Dumont L, et al. Efficacy and harm of pharmacological prevention of acute mountain sickness: quantitative systematic review. BMJ 2000; 321:267–72.
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