Study of acute mountain sickness during "rapid ascent" trekking to extreme altitude.

Acute mountain sickness (AMS) is an important cause of morbidity and mortality following acute exposure to high altitude. Several clinical variables were evaluated during the 1990 Trans-Kalindi Exploration to extreme altitude (5949 m) in 10 healthy adult lowlanders (age 31.7 +/- 6.4 yrs) who undertook a relatively rapid ascent from sea level to 5949 m with short periods of acclimatisation at 4393 m, 4898 m and 5700 m. 40% of the subjects had definite AMS. Only one subject had features of early cerebral oedema at 4393 m and had to be brought down temporarily to 3878 m. All subjects completed the trek without needing medication. Proper acclimatisation was characterised by absence of significant symptoms of AMS above 4500 m, absence of sustained tachycardia, fall in daily positive fluid balance from 1.7 +/- 0.9 (sea level) liters to 0.7 +/- 0.3 litres (at 5700 m) (p < 0.05), increase in 24 hours urinary sodium excretion from 174 +/- 78 mmol to 344 +/- 145 mmol (p < 0.01) and an increase in the ratio of urinary excretion of sodium and potassium from 3.1 (sea level) to 3.6 (5700 m). We conclude that the incidence of AMS at extreme altitude is similar to that at lower altitude. Reasonable acclimatisation is possible during the climb to extreme altitude.