- Patients with severe hypoxemia fulfilling the usual criteria for continuous oxygen therapy at study entry: PaO2 <=55 mmHg; or PaO2 <= 59 mmHg with clinical evidence of at least one of the following: (1) with right ventricular hypertrophy (P pulmonale on ECG:3 mm leads ll, lll, aVf); (2) right ventricular hypertrophy; (3)Peripheral edema (cor pulmonale); (4) hematocrit >=55%;