Altitude Sickness

Altitude sickness is a systemic issue on Mount Kilimanjaro. This is partly to do with the fact that Kilimanjaro is a high altitude trek, but more critically because the speed of ascent on most Kilimanjaro routes is relatively rapid.Acclimatization is the process by which the body becomes accustomed to lower availability of oxygen in the air and can only be achieved by spending time at various levels of altitude before progressing higher.

Oxygen, Air Density and Altitude

Acclimatization is best understood by looking at the relationship between oxygen in the air, air density and altitude changes.At sea level oxygen accounts for about 21% of air and barometric pressure is around 760 mmHg (millilitres of mercury). As one climbs in altitude the amount of oxygen in the air remains about the same (up to approximately 21,000 meters or 69,000 feet), however, air density drops and thus less pressure is put on packing oxygen molecules closer together (imagine oxygen molecules moving further and further away as altitude increases).

Blood oxygen saturation

The body deals with this decrease in available oxygen by breathing faster and deeper (even at rest) so as to increase the oxygen content in the blood (i.e. blood oxygen saturation or SO2).The chart below shows the typical profile of oxygen saturation in an average person’s blood as one ascends to higher altitudes. For the average person, you can see that blood oxygen saturation (SO2) decreases to nearly 80% at 6,000m (just above Kilimanjaro’s summit).