We evaluated extubation criteria in 48 postoperative general surgical and trauma patients receiving ventilatory support with intermittent mandatory ventilation (IMV) and continuous positive airway pressure (CPAP). Extubation criteria based on conventional respiratory mechanics demonstrated at 48% false-negative prediction of outcome, while those based on gas exchange values correctly predicted outcome in 94% of patients. Thus, conventional respiratory-mechanics extubation criteria may prolong mechanical airway and ventilatory support when used with IMV/CPAP in these patients.