Brief report: pressure support ventilation during an ascent and on the summit of Mt. Everest? A theoretical approach.

At extreme altitude, air has an almost identical composition compared to air at sea level, while its pressure is altitude-dependently lower. When supplementary oxygen is used to achieve an acceptable inspiratory pressure of oxygen (PI(O2)) during climbing, the barometric pressure difference to lower altitudes is not compensated for. In this report, we tried theoretically to apply pressure support ventilation (PSV) to partially compensate for low barometric pressures. PSV is widely used for respiratory home care and is applicable via a nasal mask. Since there are light-weight units with long battery lives on the market, we speculated that these units may to some extent replace bottled oxygen. PSV was in theory applied at barometric pressures of 400 torr (Everest Base Camp), 284 torr (South Col), and 253 torr (summit of Mt. Everest). We found that during PSV at a mean airway pressure of 16.5 torr on the summit of Mt. Everest, a fraction of inspired oxygen (FI(O2)) of 0.34 sufficed to achieve an alveolar partial pressure (PA(O2)) of 67 torr. PSV increases PI(O2) by 3.5 torr, which in theory elevates the maximum oxygen consumption (V(O2max)) by 218 mL.min(-1) in an acclimatized climber in this setting. An additional benefit of PSV at extreme altitude may come from the unloading of the respiratory muscles.