Timing of Opioid Administration and Postoperative Respiratory Depression.

The goal of this study is to determine if a relationship can be detected between the administration of an opioid and quantitative respiratory depression in spontaneously breathing non-intubated patients who have undergone general anesthesia and have received perioperative opioids. The primary aim is to determine the temporal effect of opioid administration on respiratory depression as assessed by minute ventilation with a reduction of at least 20% in the percent of predicted minute ventilation. A secondary aim is to determine a dose response of opioid administration and its effect on minute ventilation. The investigators aim to determine the influence of opioid administration on minute ventilation on spontaneously breathing patients during post-anesthesia care unit (PACU) stay.