Abstract:Objective To determine the 50% effective dose（ED 50 ）of intrathecal isobaric bupivacaine in combined spinal-epidural anaesthesia with epidural volume extension for caesarean surgery. Methods Eighty-four women undergoing elective caesarean sections were randomly assigned to seven groups, receiving intrathecally isobaric bupivacaine in a dosage of 6, 7, 8, 9, 10, 11 or 12 mg (n=12 per group), respectively. Ten mL normal saline was injected through an epidural catheter at a rate of 0.5 mL/s. Successful induction was defined as Hollmen pinprick block grade 2 at a height equal to or higher than T6. Success (surgery) was defined as success (induction) plus no requirement for epidural supplementation throughout surgery. The ED 50 values were determined using a logistic regression model. Results The ED 50 for success (induction) and success (surgery) were 8.121 mg ( 95% confidence interval: 7.421-8.821) and 9.012 mg (95% confidence interval:7.747-10.280), respectively. With increase in amount of intrathecal bupivacaine, time to success (induction) was shortened ( P 50 of 8.121 mg and 9.012 mg for success (induction) and success (surgery), respectively, in women undergoing caesarean sections.
