Air travel risk assessment:
Commercial aircraft are pressurised to cabin altitudes of 8000 feet (2438 m), at which the partial pressure of inspired oxygen falls to the equivalent of 15.1% oxygen at sea level. In healthy individuals, oxygen saturation measured by pulse oximetry decreases to 89–94% during rest and to even lower levels during exercise or sleep. Patients with pulmonary disease have lower oxygen saturation at baseline; thus, the decrease that occurs at a high altitude may result in hypoxaemia that can be severe. As an example, a stable patient with COPD with an oxygen saturation of 93% during rest at sea level may experience oxygen desaturation to 82% at rest during a commercial air flight and may experience symptoms of hypoxaemia. Even lower levels of oxygen saturation may be encountered during periods of in-flight mild exercise or sleep [271].