Intraoperative small-dose ketamine does not reduce pain or analgesic consumption during perioperative opioid analgesia in children after tonsillectomy

Objective: Ketamine inhibits the NMDA receptors via non-competitive antagonism, resulting in an antihyperalgesic effect achieved by doses of ketamine much smaller than are required for analgesia. The aim of this study was to determine the extent to which small-dose ketamine, when used in conjunction with remifentanil, has a morphine-sparing effect in the perioperative period. Materials and methods: In this randomized, double-blind, placebo-controlled prospective study, we enrolled 40 children undergoing tonsillectomy. Anesthetic care was standardized. Intraoperative analgesia was provided with remifentanil 0.5 μg × kg^-1 followed by an infusion of 0.25 μg × kg^-1 × min^-1. Group I (ketamine, n = 20) received a bolus dose of ketamine 0.5 mg × kg^-1 followed by a continuous infusion of 2 μg × kg^-1 × min^-1 before start of surgery. The infusion was stopped when surgery ended. Group II (placebo, n = 20) received normal saline in the same manner. Pain was assessed postoperatively using the Children's Hospital Eastern Ontario Pain Scale (CHEOPS; range of scores 4 - 13), and total morphine consumption was recorded in the postanesthesia care unit (PACU). Patients were transferred to the ward and morphine was administered via a patient-controlled analgesia (PCA) device and analgesia was recorded using a visual analogue scale (VAS) (0 - 10). Results: Intraoperative remifentanil consumption was not different between the ketamine group (0.29 ± 0.09 μg × kg × min^-1) and the control group (0.24 ± 0.07 μg × kg × min^-1). There were no significant differences between CHEOPS scores and VAS score between the two groups. The total mean morphine consumption in the ward was not significantly different between the two groups: 376.5 ± 91.6 μg × kg^-1 with ketamine and 384.4 ± 97.3 μg × kg^-1 with placebo. The time-to-first analgesic requirement was also similar in both groups. Conclusions: Small-dose ketamine did not decrease postoperative pain after tonsillectomy in children when added to a continuous intraoperative remifentanil infusion.