Comparison of morphine and morphine with ketamine for postoperative analgesia

The purpose of this study was to compare morphine with ketamine to morphine alone in a double-blind investigation of postsurgical pain control. Forty-two ASA 1 and 2 patients undergoing elective microdiscectomy were administered either 1 mg.ml-1 of morphine (n = 20) or 1 mg.ml-1 of both morphine and ketamine (n = 22) via iv patient controlled analgesia (IVPCA). Pain relief and side effects were assessed at 24 hr after surgery. The mean (SD) visual analogue scale (VAS) pain rating of 2.3 (1.67) for patients receiving morphine with ketamine was lower (P < 0.001) than the VAS scores of patients receiving only morphine 4.5 (1.54). Patients receiving morphine and ketamine also had less difficulty with side effects, reporting less nausea (P < 0.05), pruritus (P < 0.001), and urinary retention (P < 0.05). Although dysphoria is reported to be a common side effect of ketamine, complaints of dysphoria were rare in both groups, with only one subject (5%) in the morphine with ketamine group and three (15%) subjects receiving morphine alone reporting this side effect. IVPCA ketamine in combination with morphine provides superior postsurgical pain relief at lower dosage and with fewer side effects than morphine alone.