Ketamine, a N-methyl-d-aspartate receptor antagonist, may reduce postoperative opioid demand and improve postoperative analgesia.

Sixty-nine patients scheduled for lumbar disk surgery under general anaesthesia were enrolled in a randomised, double-blind study comparing three analgesic combinations that were started before surgical incision: morphine 0.1mgkg⁻¹ alone (group M; n=23); ketamine 0.15mgkg⁻¹ alone (group K; n=22); and a combination of morphine 0.1mgkg⁻¹ with ketamine 0.15mgkg⁻¹ (group KM; n=23). Postoperatively patient-controlled analgesia was provided with intravenous morphine. Morphine consumption was assessed during 24 H, and pain scores were measured using a visual analogue scale (VAS) at rest and on mobilisation, during the first two postoperative days.

In group KM, less i.v. morphine was administered in the post anaesthesia care unit than in group M (median [range]: 0mg [0–2] vs. 7mg [6–9], P=0.009). Cumulative 24 H morphine consumption was reduced by 57% in group KM vs. group M, and by 48% in group KM vs. group K. Postoperative VAS scores were lower in group KM vs. groups K and M. Maximal VAS score on mobilization was reduced in group KM compared to groups K and M (38mm [35–45] vs. 52mm [48–59] and vs. 59mm [55–64], in groups KM, K and M, respectively, P=0.05 and P=0.002). The incidence of postoperative nausea and vomiting was decreased in group KM compared to group M (21.7% vs. 43.5%, P=0.001).

Ketamine small-dose, combined with morphine improves postoperative analgesia and reduces opioid-related side effects in lumbar disk surgery.