Everest BC - Acclimatisation The main problem faced by climbers or trekkers is trying to climb too quickly. From a medical perspective, we are trekking in very high altitude (up to 5,500m) and in extreme altitude (summit day Kala Patthar above 5,500m). At sea level, the standard barometric pressure is 101 kPa. At 5,554m on the summit of Kala Pathhar, the standard barometric pressure is 52 kPa. This lower oxygen pressure means that there are fewer oxygen molecules in the same volume of air - there is only 51% of the oxygen available compared to sea level. Your body reacts to this lower oxygen level in a variety of ways - for example, your respiration (breathing) rate increases, and your body starts to generate more red blood cells. The respiration increase begins immediately, but the production of extra red blood cells takes longer. We allow two extra acclimatisation days during the trek at Namche Bazaar & Dingboche, where we can climb high & sleep low. This ensures that we're giving our bodies time to acclimatise to the lower oxygen levels before reaching Everest Base Camp and Kala Patthar summit. We recommend that you discuss with your GP the option of using diamox (acetazolamide) to help prevent Acute Mountain Sickness (AMS).