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Marcus RJ, Victoria BA, Rushman SC, Thompson JP. BJA 84: 739-42, 2000

Review: The authors chose to compare the effects of intramuscular ketamine 0.5-0.6 mg/kg versus intramuscular morphine 0.1-0.15 mg/kg on children status post tonsillectomy. Eighty children between the ages of 6 and 15 were randomized and received one of the two drugs after anesthetic induction. Anesthetic maintenance consisted of 1-2% halothane and 67% nitrous oxide in oxygen. Pain scores, respiratory rate, and incidence of nausea/vomiting were measured at 30, 60, 120 and 240 minutes after extubation. Rescue morphine was administered if needed in recovery and the time to first analgesic recorded.

The results revealed significant differences in the ketamine group compared to the morphine group. The ketamine group had a longer time to awaken and higher pain scores at the 30-minute measurement. Pain scores were similar at other measured times. Each group had one child who required rescue morphine in recovery. There were no significant differences between groups in the number of children requiring postoperative analgesia, time to first analgesic, respiratory rates, incidence of vomiting or dreaming.

Comments: The use of ketamine for tonsillectomy is not a new concept. Its usefulness may be in its ability to provide analgesia without causing respiratory depression or vomiting that may be associated with opioids. This was not the overall conclusion of this study. In fact, the two groups were similar in their incidence of postoperative nausea and vomiting, but this incidence was at 50%. The use of morphine did not increase this percentage. Prophylactic antiemetics may have made the comparison more useful as this is probably a more accepted clinical practice. As stated earlier, respiratory rate was also not significantly different between the two groups although ketamine should have less of an effect on respiratory drive after general anesthesia. Pain scores were similar except in the 30 minute measurement. This was not clinically significant as pain meds were not increased in the ketamine group. The conclusion of this study was therefore that ketamine is an alternative choice, but may not be superior to morphine in children who undergo tonsillectomy.

Reviewed by: Allison Kinder-Ross, MD
Duke University Medical Center