Brief report: perioperative analgesic efficacy and plasma concentrations of S+ -ketamine in continuous epidural infusion during thoracic surgery.

Background: In our study, we evaluated the analgesic effect and plasma level time course of subanesthetic doses of intraoperative S(+)-ketamine administered by continuous epidural infusion for postthoracotomic pain.

Methods: A study population of 140 patients undergoing thoracic surgery was randomly assigned to either S(+)-ketamine or ropivacaine by continuous epidural infusion. The outcome measures were as follows: (a) intraoperative fentanyl requirements; (b) postoperative pain intensity; and (c) postoperative rescue analgesics.

Results: Intraoperative fentanyl consumption was significantly lower (median of difference: -58.6 μg; 95% confidence interval [CI], -97.2 to -19.6 μg; P = 0.0032) in patients in the ketamine group than those in the ropivacaine group. Postoperative visual analog scale scores were significantly lower in the ketamine group than in controls (Wilcoxon-Mann-Whitney odds at 24 hours = 6.25; 95% CI, 4.07 to 1.97; P < 0.0001). Rescue analgesics were required more frequently in controls than in the ketamine group (percentage difference: 58.6%; 95% CI, 43.3% to 69.6%; P < 0.0001). The mean plasma level of ketamine declined rapidly during continuous epidural infusion and decayed slowly after it had stopped.

Conclusions: Our data show that epidural infusion of subanesthetic doses of S(+)-ketamine during thoracic surgery provides better postoperative analgesia than epidural ropivacaine.