BACKGROUND: Incomplete recovery of neuromuscular function may impair pulmonary and upper airway function and contribute to adverse respiratory events in the postanesthesia care unit (PACU). The aim of this investigation was to assess and quantify the severity of neuromuscular blockade in patients with signs or symptoms of critical respiratory events (CREs) in the PACU. METHODS: We collected data over a 1-yr period. PACU nurses identified patients with evidence of a predefined CRE during the first 15 min of PACU admission. Train-of-four (TOF) ratios were immediately quantified in these patients using acceleromyography (cases). TOF data were also collected in a control group that consisted of patients undergoing a general anesthetic during the same period who were matched with the cases by age, sex, and surgical procedure. RESULTS: A total of 7459 patients received a general anesthetic during the 1-yr period, of whom 61 developed a CRE. Forty-two of these cases were matched with controls and constituted the study group for statistical analysis. The most common CREs among matched cases were severe hypoxemia (22 of 42 patients; 52.4%) and upper airway obstruction (15 of 42 patients; 35.7%). There were no significant differences between the cases and matched controls in any measured preoperative or intraoperative variables. Mean (+/-sd) TOF ratios were 0.62 (+/-0.20) in the cases, with 73.8% of the cases having TOF ratios <0.70. In contrast, TOF values in the controls were 0.98 (+/-0.07) (a difference of -0.36 with a 95% confidence interval of -0.43 to -0.30, P < 0.0001), and no control patients were observed to have TOF values <0.70 (the 95% confidence interval of the difference was 59%-85%, P < 0.0001). CONCLUSIONS: A high incidence of severe residual blockade was observed in patients with CREs, which was absent in control patients without CREs. These findings suggest that incomplete neuromuscular recovery is an important contributing factor in the development of adverse respiratory events in the PACU.