Effect of epidural midazolam on the epidural analgesia with sufentanil after gynecological operation

Objective To evaluate the effect of different doses of midazolam administered epidurally on the epidural analgesia with sufentanil after gynecologic operation. Methods One hundred and twenty ASA patients aged 30-50 yr with body weight index<30 kg/m2 undergoing abdominal gynecological operation under epidnral anesthesia received continuous epidnral infusion of sufentanil for 48 h (a loading dose of 10 ml of sufentanil+continuous infiusion at 2 ml/h) after operation. The patients were randomly allocated to one of 4 groups (n=30each):group Ⅰcontrol (C) received epidural sufentanil only; group Ⅱ, Ⅲ , Ⅳ received epidural sufentanil +epidural midazolam 0.025 mg/kg (M1), 0.050 mg/kg (M2) and 0.075 mg/kg (M3) respectively. Epidural catheter was placed at L1.2 or L2.3 interspace. The severity of postoperative pain was assessed with an 100 cm VAS score. Adequate analgesia was defined as VAS score of ≤ 30 cm. Echo of epidural sufentanil was determined by up-and-down sequential technique. The initial sufentanil concentration was 1 μg/ml. Each time the concentration of epidural sufentanil increased/decreased by 20% of the previous concentration. The level of sedation was evaluated with Ramsay sedation score (1=fully awake, 6=asleep, unresponsive to verbal stimulus). The side effects were also recorded. Results The EC50 of sufentanil and 95% confidence interval were 0.87 ('0.79-0.96),0.82(0.74-60.90), 0.67 (0.61-0.74) and 0.63 (0.56-0.71) μg/ml respectively in group C, group M1, M2 and M3. EC50 was significantly lower in group M2 and M3 than in group C. The Ramsay sedation score was in the order of group M3 group M2 group M1 and group C (P<0.05). The incidences of over-sedation and respiratory depression were significantly higher in group M3 than in other 3 groups. Conclusion Epidural midazolam 0.050-0.075 mg/kg can enhance the analgesic effect of epidural sufentanil after gynecological operation. Key words: Sufentanil;  Midazolam;  Dose-response relationship, drug;  Analgesia, epidural;  Gynecologic surgical procedures