Flow chart of the study. From September 2007 to September 2008, 67 patients required tracheal intubation. Twenty-three patients were intubated for reasons other than acute respiratory failure. The remaining 44 patients were thus randomized to our two groups. Three patients were excluded before intubation because of cardiac arrest after induction (n = 2) or systolic blood pressure below 50 mmHg. The two patients excluded for cardiac arrests were patients with severe hypoxemia. Blood gases at inclusions were partial pressure of arterial oxygen (PaO2) 37 mmHg, partial pressure of arterial carbon dioxide (PaCO2) 22 mmHg, pH 7.11, serum potassium 3.9 for the first patient and PaO2 41 mmHg, PaCO2 33 mmHg, pH 7.26, serum potassium 4.1 for the second. In both cases, cardiac arrests were recovered after cardiopulmonary resuscitation. One patient was excluded because of selective intubation. Forty patients were thus ultimately included in the study. FiO2: fraction of inspired oxygen; IDS: intubation difficult scale; PEEP: positive end-expiratory pressure; VT: tidal volume.