90% effective volume of 0.1% ropivacaine combined with 0.4 µg/ml sufentanil for epidural labour analgesia with push pump at a rate of 400 mL/hr and a bolus interval of 30 min: a double-blind sequential dose-finding study

Abstract Background It was reported that either shorter programmed intermittent epidural bolus (PIEB) intervals or high-speed bolus can produce more extensive epidural spread. We hypothesized that a combination of shortened time interval and increased speed of epidural bolus might further improve analgesic effect and therefore reduce the hourly volume for epidural labour analgesia. Methods This double-blind dose-finding study used a biased coin up-and-down sequential allocation method to determine the 90% effective bolus volume of ropivacaine combined with sufentanil while using the push pump at a rate of 400 mL/hr and interval of 30 min to provide effective analgesia without breakthrough pain. We used 0.1% ropivacaine with 0.4 µg/mL sufentanil, with bolus volumes ranging from 3 to 6 mL. The first patient was assigned a volume of 3 mL, and the remaining volumes were assigned according to the biased coin-up-and-down method. Results The estimated 90% effective volume (EV90) of ropivacaine combined with sufentanil for epidural labour analgesia at a time interval of 30 min was 4.88 mL (95% confidence interval 4.83–5.38). Conclusions The optimum bolus volume of ropivacaine with sufentanil while using push pump at a time interval of 30 min is approximately 5 mL. It could probably further reduce the hourly bolus volume for epidural labour analgesia.