Abstract

High altitude pulmonary edema (HAPE) is the most common of the serious manifestations of altitude sickness, acute respiratory distress syndrome (ARDS) may be secondary to HAPE in some severe cases. The purpose of this study was to evaluate the diagnosis of ARDS at an altitude above 4000 m. Clinical studies were performed in eight patients with ARDS secondary to HAPE at an altitude of 4500m, 10 patients with pure HAPE occurred at the same altitude were as the control group. All patients were male Han sea-level residents; there was no history of cardiopulmonary disease. After an initial emergency treatment on high mountains, both HAPE and the suspected ARDS patients were rapidly descended to Golmud Hospital at an altitude of 2808 m. The major difference between ARDS and the usual clinical course of HAPE was its severity and prolonged nature. Refractory hypoxemia, higher pulmonary artery pressure, and acute respiratory failure occurred are three features which indicated that ARDS has been secondary to HAPE. In summary, our study showed that diagnosis of ARDS at high altitude (above 4000 m) are as follows: 1) Acute onset with 24-48 hr of the predisposing event (HAPE); 2) Chest X-ray shows bilateral infiltrates; 3) No evidence of elevated left atrial pressure, the pulmonary capillary wedge pressure is ≤ 18 mmHg; (4) PaO2 < 60 mmHg with PaCO₂ < 50 mmHg indicated a hypoxemic respiratory failure; 5) A ratio of arterial oxygen tension to fraction of inspired oxygen (PaO₂/FIO₂) of 100 to 150 mmHg.

Key words: High-altitude pulmonary edema, acute respiratory distress syndrome, diagnosis, the ratio of PaO2 to the fraction of inspired oxygen (PaO₂/FIO₂).