['Critically ill patients are predisposed to oxyhemoglobin desaturation during intubation.', 'To find out whether noninvasive ventilation (NIV), as a preoxygenation method, is more effective at reducing arterial oxyhemoglobin desaturation than usual preoxygenation during orotracheal intubation in hypoxemic, critically ill patients.', 'Prospective randomized study performed in two surgical/medical intensive care units (ICUs). Preoxygenation was performed, before a rapid sequence intubation, for a 3-min period using a nonrebreather bag-valve mask (control group) or pressure support ventilation delivered by an ICU ventilator through a face mask (NIV group) according to the randomization.', 'The control (n = 26) and NIV (n = 27) groups were similar in terms of age, disease severity, diagnosis at admission, and pulse oxymetry values (Sp(O(2))) before preoxygenation. At the end of preoxygenation, Sp(O(2)) was higher in the NIV group as compared with the control group (98 +/- 2 vs. 93 +/- 6%, p < 0.001). During the intubation procedure, the lower Sp(O(2)) values were observed in the control group (81 +/- 15 vs. 93 +/- 8%, p < 0.001). Twelve (46%) patients in the control group and two (7%) in the NIV group had an Sp(O(2)) below 80% (p < 0.01). Five minutes after intubation, Sp(O(2)) values were still better in the NIV group as compared with the control group (98 +/- 2 vs. 94 +/- 6%, p < 0.01). Regurgitations (n = 3; 6%) and new infiltrates on post-procedure chest X ray (n = 4; 8%) were observed with no significant difference between groups.'] Does noninvasive ventilation improve preoxygenation before intubation of hypoxic patients?