Before the oropharyngeal leak test was carried out, the face of the patient was covered so that the observer was blinded to the airway device. The oropharyngeal leak pressure was determined by transiently stopping ventilation and closing the adjustable pressure-limiting valve with a fresh gas flow of 3 L/min until airway pressure reached a steady state and a voice of leakage was heard. The airway pressure was not allowed to exceed 40 cm H2O.