Expected changes in resting oxygen saturation with increasing altitude

With the decline in barometric pressure and the ambient partial pressure of oxygen during ascent to a high altitude, the partial pressure of arterial oxygen and the oxygen saturation as measured by pulse oximetry (SpO₂) are reduced. The normal SpO₂ at a given elevation decreases to a range of values rather than to a single value because of interindividual variation in the hypoxic ventilatory response and other physiological responses to hypoxia. The values shown are estimates of the expected ranges 24 to 48 hours after ascent to a high altitude, which have been derived from values reported in published studies conducted at various altitudes.