special subjects
Air Travel
Decreased oxygen tension
In passenger jets at cruising altitude, with aircraft cabins typically pressurized to 6,000 to 8,000 feet (1830 to 2440-m) above sea level, the partial pressure of oxygen is about 25% less than at sea level, which, because of the oxygen-hemoglobin dissociation curve (see figure), represents a drop in arterial oxygen saturation of only about 4.4%. This decrease may be significant for people with severe heart or lung disease (see table) but is harmless to most people; however, after 3 to 9 hours at that altitude equivalent, some people report discomfort (eg, headache, malaise). In general, anyone who can walk 50 m or climb one flight of stairs and whose disease is stable can tolerate normal passenger jet cabin conditions without additional oxygen. However, problems may arise for travelers with moderate or severe pulmonary disease (eg, asthma, COPD [chronic obstructive pulmonary disease], cystic fibrosis), heart failure, anemia with Hb<8.5 g/dL (85 g/L), severe angina pectoris, sickle cell disease (but not trait), and some congenital heart diseases. When flying is essential, such patients can usually fly safely with specially designed continuous oxygen equipment, which must be provided by the airline. Mild ankle edema due to venous stasis commonly develops during long flights and should not be confused with heart failure. Smoking can aggravate mild hypoxia and should be avoided before flying. Hypoxia and fatigue may increase the effects of alcohol. 