Percentage of patients, 13 years and older, undergoing an inpatient or ambulatory surgical procedure who are taking methadone as outpatients or who have a prescription for methadone in their admittance documentation and where methadone is either continued or changed to an equivalent IV dose to maintain the therapeutic level regimen during the perioperative period. For patients receiving care in an ambulatory surgical setting, methadone medication was provided as scheduled before surgery.