BACKGROUND: Neuroaxial morphine may produce nausea and vomiting due to cephalad migration. Though it improves post- operative pain, it may have serious complication delaying recovery. The aim of this study was to investigate the efficacy of prophylactic antiemetics such as conventional metoclopramide or more expensive ondansetron.

METHODS: Eighty-seven patients who underwent orthopedic knee arthroscopic surgery under epidural anesthesia were randomly assigned to three groups, which are (a) normal saline intravenous injection control group (Group C), (b) metoclopramide intravenous injection and intranasal spray study group (Group M), (c) ondansetron inravenous injection group (Group O). Before the end of surgery, all patients were given 3 mg of morphine and 2 mg of butorphanol mixture via epidural catheter for postoperative pain control. The anesthesia were all standardized. Post-operative nausea and vomiting were observed and used as outcome variables and postoperative pain, itching, somnolence, dizziness, urinary retention were also observed.

RESULTS: The incidence of postoperative nausea was significantly lower in Group M (P = 0.0296) and Group O (P = 0.005) compared with Group C. The incidence of postoperative vomiting was significantly lower in Group O (P = 0.01) compared with Group C. But statistically no difference was noted in vomiting between Group C and Group M (P = 0.0579).

CONCLUSIONS: The results suggest that ondansetron and metoclopramide are effective in reducing the incidence of post-operative nausea. But ondansetron is more effective in reducing the incidence of post-operative morphine induced vomiting.