High-altitude pulmonary edema (HAPE) is a rare cause of pulmonary edema that presents with dyspnea on exertion, dry cough, tachypnea, and sometimes blood-tinged or pink frothy sputum. It is the most common fatal manifestation of altitude illness.
HAPE develops after rapid ascent to high altitudes, typically those above 2500 meters (about 8000 feet). Onset is usually within 2-4 days. Altitude-induced changes in pulmonary vasculature (increased sympathetic tone, vasoconstriction) along with uneven perfusion of pulmonary vasculature leads to increased pulmonary capillary pressure, with failure of capillaries and leak of fluid across alveoli.