Small-dose S(+)-ketamine reduces postoperative pain when applied with ropivacaine in epidural anesthesia for total knee arthroplasty

Reduction of nociceptive input through blockade of N-methyl-D-aspartate (NM DA) receptors has been reported. We compared the effects of epidural S(+)ke tamine versus placebo on postoperative pain in a randomized, double-blinded study in 37 patients undergoing unilateral knee arthroplasty. After lumbar epidural anesthesia with ropivacaine (10 mg/mL, 10-20 mt), 19 patients rec eived 0.9% epidural saline, and 18 patients received 0.25 mg/kg epidural S( +)ketamine 10 min before surgical incision. After surgery, patient-controll ed epidural. analgesia with ropivacaine was provided. During the first 8 h after surgery, visual analog scale pain rating was similar between groups. Twenty-four and 48 h after surgery, patients anesthetized with ropivacaine had higher visual analog scale ratings at rest and during movement (P < 0.0 5) than patients anesthetized with S(+)-ketamine and ropivacaine. Forty-eig ht hours af ter surgery, patients anesthetized with ropivacaine also consum ed more ropivacaine (558 +/- 210 mg) (P < 0.01) than those anesthetized wit h S(+)-ketamine and ropivacaine (319 +/- 204 mg). Adverse events were simil ar between groups. Patients who received S(+)-ketamine and ropivacaine rate d the quality of their pain therapy better than those who received ropivaca ine alone (P < 0.05). We conclude that the combination of S(+)-ketamine and ropivacaine in epidural anesthesia increases postoperative gain relief whe n compared with ropivacaine.