Postoperative pain: the effect of low-dose ketamine in addition to general anesthesia

In a randomized, double-blind study, postoperative pain was assessed in 22 patients undergoing elective open cholecystectomy with two types of anesthesia: standardized general anesthesia (control group), and low-dose ketamine as an addition to the same method of general anesthesia, before surgical incision (ketamine group). After the operation we found that the time from the end of surgery to the first request for analgesic was longer in the ketamine group. Postoperatively, patients in both groups were treated with patient-controlled analgesia (PCA) in exactly the same way. The major difference in the study was the reduced dose requirement of morphine in the ketamine group compared with the control group after the operation. The mean dose of morphine given in patients of the control group during the first 24 h was 48.7 mg vs 29.5 mg in the ketamine group. Mean visual analog scale (VAS) and verbal rating scale (VRS) were higher in patients in the control group during the first 5 h after surgery (P < 0.02), but between 5 and 24 h after surgery VAS and VRS were not significantly different (P > 0.05). Our results indicate that postoperative pain can be decreased when ketamine in low doses is added to general anesthesia before surgical stimulation.