Correspondence
High-Altitude Illness
N Engl J Med 2001; 345:1279-1281October 25, 2001
- Article
To the Editor:
Altitude sickness is common in the Himalayas, where thousands of people come for trekking every fall and spring. For those of us who offer health care in Nepal to travelers at high altitude (which Peter Hackett helped to start many years ago) the review by Hackett and Roach (July 12 issue)1 was fascinating, but I do have a few comments.
More than overhydration, the great danger in the mountains is dehydration due to the general unavailability or poor quality of water or to the lack of thirst. Dehydration may simulate acute mountain sickness, as the authors suggest. It may also interfere with proper acclimatization2 and aid in the pathogenesis of acute mountain sickness.3 Hence, at our clinic we advise drinking adequate water (without going to extremes) so that the urine is clear. Epidemiologic studies have shown that respiratory infections may predispose persons to acute mountain sickness and not only to high-altitude pulmonary edema.3,4 Therefore, persons with symptoms of a cold or influenza before a trek or a climb must be more cautious.
In the Himalayas, we caution people not to sleep more than 400 m above their sleeping altitude of the previous night, when this is logistically possible, although data regarding the effect of changes in sleeping altitude are lacking; 600 m may be too large a change. Finally, impaired cerebral autoregulation may contribute to high-altitude cerebral edema, as suggested, but my colleagues and I were amazed to find in a study we conducted that even healthy, well-adapted Sherpas had impaired cerebral autoregulation at 4300 m.5
5 ReferencesBuddha Basnyat, M.D.
Nepal International Clinic, Katmandu, Nepal
nic@naxal.wlink. com. np 1
Hackett PH ,Roach RC . High-altitude illness. N Engl J Med 2001;345:107-114
Full Text | Web of Science | Medline2
West JB. High life; a history of high altitude physiology and medicine. Oxford, England: Oxford University Press, 1998:343.
3
Basnyat B ,Lemaster J ,Litch JA . Everest or Bust: a cross sectional, epidemiological study of acute mountain sickness at 4243 meters in the Himalayas. Aviat Space Environ Med 1999;70:867-873
Web of Science | Medline4
Murdoch DR . Symptoms of infection and altitude illness among hikers in the Mount Everest region of Nepal. Aviat Space Environ Med 1995;66:148-151
Web of Science | Medline5
Jansen GFA ,Krins A ,Basnyat B ,Bosch A ,Odoom JA . Cerebral autoregulation in subjects adapted and not adapted to high altitude. Stroke 2000;31:2314-2318
CrossRef | Web of Science | Medline
To the Editor:
Hackett and Roach recommend that adults take acetazolamide at a dose of 125 mg twice a day to prevent high-altitude illness. They state that this low dose is as effective as larger doses, while implying that the minimal effective dose remains uncertain. Unfortunately the reference they cite1 does not support this assumption. After a systematic review, Dumont et al.1 concluded that 750 mg of acetazolamide was more effective than placebo, regardless of the rate of ascent (relative risk, 2.18; 95 percent confidence interval, 1.52 to 3.15), whereas a dose of 500 mg was not significantly more effective than placebo (relative risk, 1.22; 95 percent confidence interval, 0.93 to 1.59). Although it is likely that a dose of 750 mg would be associated with a higher incidence of paresthesia and polyuria than would the 250-mg dose suggested by Hackett and Roach, it does not seem reasonable to use a dose that is unlikely to provide any benefit and yet may have adverse effects.
1 ReferencesR.I. Ogilvie, M.D.
Toronto Western Hospital, Toronto, ON M5T 2S8, Canada
ri.ogilvie@utoronto. ca 1
Dumont L ,Mardirosoff C ,Tramer MR . Efficacy and harm of pharmacological prevention of acute mountain sickness: quantitative systematic review. BMJ 2000;321:267-272
CrossRef | Web of Science | Medline
To the Editor:
The use (and potential abuse) of dexamethasone at high altitude is becoming more commonplace. Although somewhat controversial, dexamethasone does not enhance the acclimatization process or reduce objective physiological abnormalities related to exposure to high altitudes but, rather, suppresses the symptoms of acute mountain sickness.1 Severe rebound illness can occur when it is discontinued at high altitude.2 For these reasons, dexamethasone should not be used immediately before or while ascending to a higher altitude, but should be reserved for treatment on descent or when descent to a lower altitude must be delayed.
With increasing frequency, modern high-altitude climbers favoring the “alpine-style” method of short, rapid ascents to high altitudes are using dexamethasone prophylactically immediately before their climbs, risking rebound disease in the event that they are unable to descend quickly. Most alpine-style climbers are able to avoid serious high-altitude illness by descending before the sequelae of hypoxemia incapacitate them. Others are increasingly pushing their limits from hours to days at very high altitudes, sustained by dexamethasone, which is a potentially dangerous strategy.
2 ReferencesAndrew P. White, M.D.
Yale University School of Medicine, New Haven, CT 06510
andrew.white@yale. edu 1
Levine BD ,Yoshimura K ,Kobayashi T ,Fukushima M ,Shibamoto T ,Ueda G . Dexamethasone in the treatment of acute mountain sickness. N Engl J Med 1989;321:1707-1713
Full Text | Web of Science | Medline2
Hackett PH ,Roach RC ,Wood RA , et al. Dexamethasone for prevention and treatment of acute mountain sickness. Aviat Space Environ Med 1988;59:950-954
Web of Science | Medline
To the Editor:
Hackett and Roach refer to studies suggesting that a deficiency of nitric oxide may underlie the development of symptoms in vulnerable persons. I was surprised that they did not mention the therapeutic use of this gas in treating high-altitude pulmonary edema. Studies have found it to be beneficial at concentrations from 10 to 40 parts per million,1,2 with improvement in clinical findings such as rales, as well as in findings on chest radiography.1 Nitric oxide also markedly reduced the mean systolic pulmonary-artery pressure and improved oxygenation in susceptible mountaineers, although it worsened both in their colleagues who were resistant to high-altitude pulmonary edema.2 In patients with high-altitude pulmonary edema, the effect on oxygenation of oxygen supplemented with nitric oxide significantly exceeds that of oxygen alone.3 Since these effects occur rapidly, the administration of nitric oxide could be of critical value in severe cases of this illness.
3 ReferencesBrian O'Brien, M.Med.Sc., F.C.A.R.C.S.I.
Beaumont Hospital, Dublin 9, Ireland
drobrien@hotmail.com 1
Wang W ,Zhang X ,Ma Y . Low-concentration nitric oxide inhalation in the treatment of high-altitude pulmonary edema. Zhonghua Jie He He Hu Xi Za Zhi 1998;21:212-214
Medline2
Scherrer U ,Vollenweider L ,Delabays A , et al. Inhaled nitric oxide for high-altitude pulmonary edema. N Engl J Med 1996;334:624-629
Full Text | Web of Science | Medline3
Anand IS ,Prasad BA ,Chugh SS , et al. Effects of nitric oxide and oxygen in high-altitude pulmonary edema. Circulation 1998;98:2441-2445
Web of Science | Medline
Author/Editor Response
The authors reply:
To the Editor: We agree with Dr. Basnyat that dehydration in the mountains is a concern, but no compelling data confirm that dehydration has a role in acute mountain sickness. The report he cites demonstrated a correlation between lower water intake and acute mountain sickness, but causality could not be established; persons with acute mountain sickness are often nauseated and therefore have reduced fluid intake. The only well-controlled investigation found no effect of hydration status on the development of acute mountain sickness.1 As for the rate of ascent, 600 m per day may indeed be too rapid for some, whereas for others, 400 m per day is agonizingly slow. Such is the problem with offering general guidelines.
We cited the article by Dumont et al. only to acknowledge the uncertainty regarding the lowest effective dose of acetazolamide. Unlike Dr. Ogilvie, we consider the conclusion by Dumont et al. invalid, for reasons that have already been described elsewhere.2,3 In fact, 500 mg of acetazolamide per day is helpful during rapid ascent.2,3 Only studies directly comparing different doses of acetazolamide will be able to establish the optimal dose; the meta-analysis of Dumont et al. does not.
Dr. White highlights the risk of dexamethasone abuse. Dexamethasone should not be used for routine prophylaxis, since it does not enhance acclimatization, as acetazolamide does. However, it is useful for those who have an intolerance to acetazolamide, preferably in the setting of rapid ascent to a high altitude with no further ascent until acclimatization has occurred. We agree that its use as a performance-enhancing agent at high altitude is dangerous. In addition, dexamethasone does not prevent high-altitude pulmonary edema, a deadly risk for those who push their limit of acclimatization.
In response to Dr. O'Brien: we did not mention nitric oxide as a therapeutic agent for high-altitude pulmonary edema because no clinical advantage over oxygen has yet been demonstrated, and its use is impractical in the field. Oxygen is remarkably effective for the rapid resolution of high-altitude pulmonary edema. Whether the finding of Anand et al.4 that oxygen combined with nitric oxide is more effective than either alone for decreasing pulmonary vascular resistance will translate into a clinical benefit remains unknown. Perhaps the combination will prove useful for the occasional victim who does not have a prompt response to oxygen. Only a clinical trial can answer this question.
4 ReferencesPeter H. Hackett, M.D.
International Society for Mountain Medicine, Ridgway, CO 81432
hackett@ismmed.org Robert C. Roach, Ph.D.
New Mexico Resonance, Albuquerque, NM 871081
Aoki VS ,Robinson SM . Body hydration and the incidence and severity of acute mountain sickness. J Appl Physiol 1971;31:363-367
Web of Science | Medline2
Hackett P . Pharmacological prevention of acute mountain sickness: many climbers and trekkers find acetazolamide 500 mg/day to be useful. BMJ 2001;322:48-48
CrossRef | Web of Science | Medline3
Bartsch P ,Schneider M . Pharmacological prevention of acute mountain sickness: same ascent rates must be used to assess effectiveness of different doses of acetazolamide. BMJ 2001;322:48-48
CrossRef | Web of Science | Medline4
Anand IS ,Prasad BA ,Chugh SS , et al. Effects of nitric oxide and oxygen in high-altitude pulmonary edema. Circulation 1998;98:2441-2445
Web of Science | Medline
- Citing Articles (3)
Citing Articles
1
Alan Richardson, Peter Watt, Neil Maxwell. (2009) The effect of hypohydration severity on the physiological, psychological and renal hormonal responses to hypoxic exercise. European Journal of Applied Physiology 106:1, 123-130
CrossRef2
(2002) Sightings. High Altitude Medicine & Biology 3:1, 9-16
CrossRef3
Sudhir Kumar Jha, Anil C. Anand, Vivek Sharma, Nikhil Kumar, Chandra M. Adya. (2002) Stroke at High Altitude: Indian Experience. High Altitude Medicine & Biology 3:1, 21-27
CrossRef
