ObjectiveNoninvasive positive pressure techniques such as continuous and bilevel positive airway pressure avoid intubation and its attendant complications in selected patients with acute respiratory failure. However, mask intolerance remains a common cause for failure of noninvasive ventilatory techniques. The aim of our study was to assess patient tolerance of oronasal vs. nasal mask ventilation in acute respiratory failure.DesignRandomized, controlled trial.SettingEmergency department or intensive care units at a university hospital.PatientsSeventy patients with acute respiratory failure as evidenced by clinical or blood gas criteria.InterventionsPatients randomly received either a disposable nasal or an oronasal mask (Respironics, Pittsburgh, PA) when they met study criteria.Measurements and Main ResultsThirty-five patients were randomized into each arm of the study; most of the patients had acute cardiogenic pulmonary edema (48.6% of the nasal mask group and 42.8% of the facial mask group) or chronic obstructive airway disease (34.3% of the nasal mask group and 31.4% of the facial mask group). Baseline clinical characteristics of the two groups of patients were similar. Heart and respiratory rates and blood gases improved similarly for patients in both mask groups. Rates of intubation were also similar (eight in each group). However, mask intolerance was significantly higher in the nasal than the oronasal mask group (12 vs. 4, respectively,p= .023). Four patients in the nasal (11.4%) and two in the oronasal mask group (5.7%) died later during the hospitalization. The overall success rate tended to be greater in the oronasal (65.7%) than the nasal group (48.6%), but the difference was not statistically significant.ConclusionAlthough both masks performed similarly with regard to improving vital signs and gas exchange and avoiding intubation, the nasal mask was less well tolerated than the oronasal mask in patients with acute respiratory failure.