High-altitude pulmonary edema is a form of severe altitude illness. It is a life-threatening condition that occurs when the lungs fill with edema or fluid. Those with high-altitude pulmonary edema will commonly complain of extreme fatigue and shortness of breath (even at rest). Their breathing usually becomes fast and shallow. A cough will develop and can have frothy or pink sputum. Their breath can become gurgling or rattling and they will experience chest tightness. If their oxygen levels are low, blue or gray lips or fingernails will be noticeable.
(This answer provided for NATA by the Marist College Athletic Training Education Program.)