Altitude Sickness and Adventure Travel
Abstract & Commentary
By Carol A. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases, Santa Clara Valley Medical Center, is Associate Editor for Infectious Disease Alert
Dr. Kemper reports no financial relationships relevant to this field of study.
Sources: Leshem E, et al. Clinical features of patients with severe altitude illness in Nepal. J Travel Med. 2008;15:31-322; Kupper TEAH, et al. Low-dose theophylline reduces symptoms of acute mountain sickness. J Travel Med. 2008;15:307-314.
Adventure travel and ecotourism has become a huge industry, and certain destinations are becoming ever more popular. Current estimates suggest that more than 80,000 people travel annually to Nepal alone to trek. People come from all over the world, are of all ages, and some, it turns out, are not in the greatest shape and have underlying medical problems. Many of these individuals frequently ascend to > 5,500 m over a period of 1-3 weeks; the highest altitude attained with the normal trekking permit is 5,600 m (18,400 feet), though a special permit may be obtained allowing climbers to attempt peaks from 5,600 m to 8,848 m. The risk of altitude sickness in these travelers is not trivial, as suggested by the increased frequency of annual evacuations off the mountains. Current estimates suggest that up to 30%-40% of persons trekking above 4,000 m develop some form of altitude sickness.
Lesham et al assessed the clinical and demographic features of patients seen and evaluated for altitude-related illness at the CIWED Clinic Travel Medicine Centre in Kathmandu, Nepal (located at 1,310 m), from 1999 to 2006. A total of 406 patients meeting criteria for some form of altitude-related illness were included in the study (some retrospectively), ranging in age from 15 to 73 years; 85% trekked with an organized group. Patients were grouped according to findings consistent with high-altitude cerebral edema (21%), high-altitude pulmonary edema (34%), both (27%), or acute mountain sickness (AMS) (18%). Demographic characteristics were compared with that of 39,402 trekkers without altitude-related illness (obtained from the permit registry), who served as a control group. In general, compared with controls, patients with altitude-related illness were older (38.6 vs 44 yrs, p < .0001), and were more frequently male. Prophylactic acetazolamide was used less frequently in patients with high-altitude cerebral edema (28%) and patients with high-altitude pulmonary edema (29%), compared with 43% of those with AMS (p < .001); (similar information on controls was not available). Nearly 6% of patients with altitude-related illness had a history of significant medical problems, including hypertension, heart disease, asthma, diabetes, or stroke.
While most trekkers chose to climb less risky areas, such as the Anapurnas, individuals with altitude-related illness were more likely to have trekked Everest, where the ascent was nearly twice as rapid and the maximal altitude greater than in other areas. Most evacuations and deaths were of Everest climbers. Twenty-one deaths due to altitude-related illness were recorded by 8 of the 18 local embassies. The estimate of altitude-related death in Nepal was 7.7 per 100,000 trekkers.
Lesham et al recommend that current recommendations for altitude gain per day be adjusted downward, especially in the Everest area, although this means a climb will take longer. Although one might imagine that group trekking would be safer, the authors contend that it is characterized by a more rigorous schedule, with peer pressure to stay with the group despite early warning signs of fatigue and illness. It is worth noting that 33% of those with altitude-related illness received prophylactic acetazolamide.
In a second, smaller, randomized, placebo-controlled study, Kupper et al examined the efficacy of low-dose, slow-release theophylline 300 mg daily in 17 healthy male volunteers in the reduction of AMS. The mean age was 35 yrs, and all of the patients were experienced recreational climbers. The study was conducted on Monte Rosa in Italy at 4,559 m. A 12-channel sleep recorder recorded sleep and breathing parameters throughout the night.
Theophylline was well-tolerated, and no participant developed high blood pressure during the study. AMS symptoms were significantly less frequent in individuals receiving theophylline compared with placebo, and none of the individuals receiving theophylline had an elevated mean AMS score at any time at the intermediate altitude of 3440 m. During ascent and during all five days at the highest altitude of 4,559 m, the difference in symptoms between the groups was still significant. Periodic breathing events (34 vs 74 per hr, p < .05) and oxygen desaturations (62 vs 122 per hr, p < .01) were also significantly reduced in theophylline recipients compared to the placebo group. Kupper et al believe theophylline stimulates the respiratory drive, thereby reducing the risk of sleep disorder breathing, which adds to the hypoxic burden of high altitude.