Unilateral high-altitude pulmonary edema (HAPE): a case report and discussion of pathophysiology

High-altitude pulmonary edema (HAPE), a potentially life-threatening altitude adaptation disorder, is considered to be caused by an exaggerated increase in pulmonary blood pressure and a non-cardiogenic rise in pulmonary vascular permeability subsequent to alveolar hypoxia. A 40-year-old male mountaineer was affected by an advanced stage of HAPE at high altitude (Monte Rosa plateau, 4000 m). The symptoms abated immediately after the patient descended from the altitude. However, six hours after the symptoms had resolved, radiographic signs of pulmonary edema, confined to the right lung, were seen. This rarely described unilateral radiological pattern of HAPE resolved completely within two days. We suggest that aspiration events of nasal secretion, the right sleeping position at night and an elevated right diaphragm reduced the patient's compensatory hyperventilation capacity of the right lung. The resulting increased alveolar hypoxia in the right lung was responsible for unilateral edema. The pathophysiological mechanism underlying unilateral HAPE is discussed.