Flight conditions:
(1) Commercial airlines frequently fly at 22,000 to 44,000 feet above sea level, but are pressured to an equivalent of 5,000 to 8,000 feet, which is associated with a reduced oxygen partial pressure.
(2) Flying without pressurization or the loss of cabin pressure can result in sudden drops in the partial pressure of oxygen.
Indications for use of supplemental oxygen during travel in commercial airlines:
(1) use of oxygen at baseline altitude
(2) PaO2 < 70 mm Hg.
(3) New York Heart Association Class III or IV congestive heart failure
(4) unstable angina
(5) cyanotic congenital heart disease
(6) primary pulmonary hypertension
(7) severe anemia (hemoglobin < 8.5 g/dL)
(8) sickle cell anemia or unstable hemoglobinopathy
Patient preflight evaluation:
(1) The PaO2 is the most useful test, especially if measured shortly before the flight. Patients with an elevated PaCO2 may be at increased risk even with supplemental oxygen. Supplemental oxygen is recommended for patients who may develop a PaO2 < 50 mm Hg at any airborne altitude.
(2) A hypoxia-altitude stimulation test (HAST) test using a 15% oxygen breathing mixture, oximeter or arterial catheter, and an electrocardiogram may be done. This can be combined with exercise testing.
(3) Simple exercise testing (walking 50 yards, climbing one flight of stairs) can be used to screen for severe dyspnea on exertion.
