The Effect of a Large Dose of Epidural Ketamine for Postoperative Pain Relief

Won, Chi Hwan; Suh, Jae Hyun

Abstract

Intrathecal and epidural narcotics have been widely used since 1979 to relieve pain and provide postoperative analgesia. Ketamine hydrochloride, a potent analgesic and anesthetic, has also been studied to its usefulness in epidural administration for postoperative pain relief devoid of the respiratory depression caused by morphine. This study was performed to evaluate whether a large dose of ketamine is effective for postoperative pain relief and the results were compared with those of epidural morphine. Forty patients undergoing lower abdominal and extremity surgery were randomly assigned in two groups of twenty. No patient was receiving narcotics or analgesic at the time of study. The operative anesthesia was provided by continuous epidural anesthesia with 27 ml of 1.5% lidocaine with 1:200,000 epinephrine. Ketamine 30mg or morphine 3-4 mg was administered about 30 minutes before the end of operation through the epidural catheter respectively. Patients were monitored every 15 minutes during the first hour and every hour during first 24 hours. Pain complaint, respiratory rate, heart rate, blood pressure, SaO2 and potential side effects were recorded. The results were as follows; 1) Two cases in the ketamine group and nine cases in the morphine group did not need the additional analgesics after operation. The duration of pain relief in the ketamine group varied from 1.83 hour to over 48 hours (less than 3 hours in 50% of patients). Mean analgesic time in the morphine group was 28.3+/-5.6 hours. 2) Dissociative anesthesia with hypotension (one), sedation (fifteen), dizziness (seven), nausea (six) and vomiting (six) in the ketamine group, whereas nausea (nine), and vomiting (five) in the morphine group were developed. We conclude that ketamine 30 mg administered epidurally, which had a more central actions and less analgesic effect than morphine, is inadequate for postoperative pain relief after lower abdomimal and extremity surgery.