Intraoperative low-dose S-ketamine has no preventive effects on postoperative pain and morphine consumption after major urological surgery in children

BACKGROUND: Clinical studies suggest low-dose ketamine may have preemptive effects on postoperative pain in adults. The objective of this study was to determine whether intraoperative low-dose S-ketamine reduces postoperative pain and morphine consumption in children undergoing major urological surgery. MATERIALS: Thirty children scheduled for major urological surgery were included in this prospective study. Anesthesia was performed as total intravenous anesthesia (TIVA) with alfentanil and propofol. Fifteen patients additionally received an intravenous bolus of S-ketamine (0.2 mg.kg-1) followed by a continuous infusion of 5 microg.kg-1.min-1, which was stopped immediately after skin closure (Ketamine Group). Another 15 patients received an infusion of saline (Control group). After transfer to the PACU, pain intensity was evaluated using a numeric rating scale (NRS). First patient controlled analgesia (PCA) request, cumulative morphine consumption and pain intensities within the first 72 h were compared. RESULTS: Morphine consumption was not significantly different during the first 72 h (Control: 0.4 mg.kg-1, 0.24-0.51 mg.kg-1, Ketamine: 0.32 mg.kg-1, 0.19-0.61 mg.kg-1; median, 25-75% percentile; n.s.). However, differences were found in pain intensity during the first postoperative hour (Control: 4.0, 3.2-4.6, Ketamine: 2.5, 1.3-3.5; median, 25-75% percentile; P<0.05) and in the time to first PCA use (Control: 37, 28-46 min, Ketamine: 62, 38-68 min; median, 25-75% percentile; P<0.05). CONCLUSIONS: Intraoperative low-dose S-ketamine had no effect on morphine consumption during the first 72 h after surgery. The differences in pain intensity and time to first PCA use probably reflect additional sedation and antinociceptive effects of S-ketamine rather than a true 'prevention' of pain.