Effect of low dose ketamine on perioperative analgesia in patients undergoing open abdominal hysterectomy - A double-blind, randomized, placebo-controlled trial

Background: Low-dose ketamine can provide effective perioperative analgesia while reducing its side effects. This study aims to estimate the effect of a low dose of ketamine administered preemptively and during the surgery on postoperative opioid requirement and the incidence of side effects of ketamine. Methods: This prospective, double-blind, randomized control trial enrolled 60 adult women (>18 years) scheduled for open abdominal hysterectomy. All patients received general anesthesia using a standard protocol. Patients were randomized to receive 0.2 mg/kg of ketamine as bolus before induction of anesthesia, followed by an infusion of 0.002 mg/kg/min for the duration of surgery (Group K) or an equivalent volume of 0.9% saline (Group C). The primary outcome was to compare the morphine requirement over the 24 h postoperatively between the two groups. The secondary outcomes were to compare the intraoperative morphine requirement, and the incidence of side effects of ketamine. Results: The intraoperative morphine requirement was significantly less (P = 0.006) in those who received ketamine (6.5 +/- 1.5 mg) compared to the placebo (7.67 +/- 1.7 mg). The 24-hour morphine requirement was less in the Group K (7.87 +/- 4.7 mg) compared to Group C (9.2 +/- 4.5 mg), but was not statistically significant. The incidence of hallucination and nystagmus was significantly higher in the ketamine group, but it lasted <2 h. Conclusion: The preemptive and the intraoperative infusion of low-dose ketamine decreases the morphine requirement intraoperatively but not during the postoperative period.