Comparison of opioid requirements and analgesic response in opioid-tolerant versus opioid-naïve patients after total knee arthroplasty

Study Objectives. To compare opioid requirements in opioid-tolerant and opioid-naïve patients after total knee arthroplasty, and to compare pain scores, sedation scores, and adverse effects between the groups. Design. Prospective, observational study. Setting. Academic medical center. Patients. Twenty-nine patients aged 18 years or older who underwent elective total knee arthroplasty between October 1, 2005, and June 31, 2007. Measurements and Main Results. Patients were classified on the basis of their daily opioid consumption during the week before surgery: those who required 10 mg or less of oral morphine equivalent were considered opioid naïve (20 patients), and those who required at least 30 mg of oral morphine equivalent were opioid tolerant (nine patients). Postoperative opioid consumption, pain scores, sedation scores, and adverse effects were compared between the two groups up to 48 hours after discharge from the postanesthesia care unit (PACU). Postoperative opioid consumption (in intravenous morphine equivalents) was significantly greater in the opioid-tolerant group than in the opioid-naïve group in the PACU (median 56 vs 8.2 mg, p=0.0013), during the first 24 hours after discharge from the PACU (108 vs 20.5 mg, p=0.0004), and 24-48 hours after discharge from the PACU (152.3 vs 25 mg, p=0.0001). Pain scores, assessed by using a verbal numeric scale from 0-10, were significantly greater in the opioid-tolerant group than in the opioid-naïve group during the first 24 hours after discharge from the PACU (5.9 vs 4.1, p=0.03). We observed no significant difference in pain scores during the other time periods studied. Sedation scores and adverse effects were similar between groups. Conclusion. After total knee arthroplasty, patients tolerant to opioids required significantly more opioids in the PACU and up to 48 hours after discharge from the PACU than did opioid-naïve patients. Opioid-tolerant patients also experienced greater pain during the first 24 hours after discharge from the PACU; however, sedation scores and adverse effects did not appear to be significantly different at any of the time periods studied. Clinicians need to be aggressive with pain management immediately after surgery and ensure that patients restart any opioid treatment at home as soon as possible.