Is it time to revise the acclimatization schedule at high altitude? Evidence from a field trial in Western Himalayas

Abstract Background In Western Himalayas, Indian Army soldiers take 11 days (6 days of acclimatization and 5 days of travel) on a sea-level to high altitude road (SH road) to reach a high altitude location (HAL) situated at an altitude of 11,500 feet from sea-level location (SLL) at an altitude of 1150 feet while following acclimatization schedule (AS). AS has an extra safety margin over the conventional ‘mountaineering thumb rule’ of not exceeding 500 m sleeping altitude above 3000 m altitude. We carried out this randomised field trial to study the feasibility of moving large number of troops rapidly from SLL to HAL on SH road in western Himalayas in 4 days under pharmaco-prophylaxis. Methods Based on the pharmaco-prophylaxis, at SLL 508 healthy lowland soldiers were divided into two groups: ‘A’ ( n  = 256) with Acetazolamide + Dexamethasone and ‘B’ ( n  = 252) with Acetazolamide + Placebo. They travelled rapidly by road to HAL in 4 days and prevalence of acute mountain sickness (AMS), high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE) during the ascent was measured. Results Prevalence of AMS was found to be 1.56% and 1.59% in group ‘A’ and group ‘B’ respectively during the ascent with no cases of HAPE and HACE. Conclusion At least on SH road, troops can be inducted rapidly to HAL from SLL in 4 days under pharmaco-prophylaxis with Acetazolamide with minimal occurrence of acute high altitude illnesses.