Patients that have problems with oxygenation at sea level are going to have even more problems at higher elevations where the barometric pressure and oxygen partial pressure are lower. During commercial aircraft travel the cabin pressure is required by U.S. Federal regulations to be pressurized to at least 565 mm Hg which is the equivalent of 8000 feet altitude. It has been reported that most airliners are pressurized to an equivalent altitude of between 5000 and 8000 feet but this will depend on both the airplane and the airline in question.
There is a general relationship between a patient’s PaO2 at sea level and their PaO2 at altitude and a variety of studies have developed equations to predict an individual’s PaO2 at altitude using ABG, spirometry, DLCO and exercise SpO2 results. These prediction equations however, have been shown to have poor accuracy when compared to a Hypoxia Altitude Simulation Test (HAST).