The effect of ondansetron on the analgesic efficacy of tramadol for postoperative patient-controlled intravenous analgesia

Objective To investigate the effect of ondansetron on the analgesic efficacy of tramadol for postoperative patient-controlled intravenous analgesia (PCIA). Methods Forty ASA I - II patients aged 22-74 years, weighing 40-90 kg scheduled for radical mastectomy were randomly allocated to one of two groups : control group ( n = 20) and ondansetron group ( n = 20) . The patients were premedicated with intramuscular atropine 0.01 mg·kg-1 and diazepam 0.2 mg·kg-1. Anesthesia was induced with midazolam 0.1-0.2 mg (total dose was limited to 15 mg), fentanyl 2.4μg·kg-1 , propofol 1.5-2.0 mg·kg-1 and vecuronium 0.12-0.15 mg·kg-1 . The patients were mechanically ventilated after tracheal intubation (VT 8-10 ml·kg-1 , RR 13 bpm). Anesthesia was maintained with enflurane inhalation and continuous infusion of vecuronium. The patients were attached to a PCIA pump after operation and received PCIA with 1 % tramadol (background infusion 2 ml·h-1 , bolus dose 2 ml, lockout interval 10min) in both groups. In ondansetron group the patients received ondansetron 6 mg iv during operation and a loading dose of tramadol 1 mg·kg-1 and ondansetron 2 mg after operation before PCIA. Pain score (VAS 0-10), sedation score (0-3), tramadol consumption and the incidence of nausea and vomiting were recorded at 4, 8, 12 and 24 h after operation. Results There was no significant difference in pain and sedation scores and the incidence of vomiting between the two groups. Significantly more tramadol was consumed at 4, 8 and 12 h after operation in the ondansetron group as compared with control group (P 0.05). Pain scores were less than 4 and no other analgesic was used in both groups. The incidence of nausea was higher in ondansetron group than that in control group ( P 0. 05 ) . Conclusion Tramadol offers satisfactory analgesia for patients after radical mastectomy. Ondansetron does not reduce the incidence of nausea and vomiting induced by tramadol but decreases the analgesic efficacy of tramadol instead.