Fig. 2. (  Top ) Pharmacokinetic modeling of the plasma concentration (expressed as concentration/ISOMAC⁵⁰on the  y -axis) of alfentanil (A), fentanyl (F), and sufentanil (S) during the intraoperative, the postanesthesia care unit, and the ambulatory surgical unit (ASU) periods and after discharge from the ASU. The  x -axis is time (minutes) from the induction of anesthesia. (  Bottom ) The incidence of postoperative nausea and vomiting (nausea, retching, or vomiting) during the postanesthesia care unit and the ASU period and after discharge from the ASU.