Dose Requirement of Intrathecal Bupivacaine for Cesarean Delivery Is Similar in Obese and Normal Weight Women

Abstract

The effect of BMI on the spread of intrathecal bupivacaine is controversial. This study assessed the ED95 of intrathecal bupivacaine for elective cesarean delivery in obese and normal weight women. We studied normal weight (BMI < 25 kg x m(-2)) and obese (BMI > 30 kg x m(-2)) women with singleton term pregnancies undergoing elective cesarean delivery. The study was conducted as a single blinded, up-down sequential allocation study (modified by the Narayana rule). All patients received a combined spinal-epidural anesthesia with a variable intrathecal dose of hyperbaric 0.75% bupivacaine, plus fentanyl 10 microg and morphine 100 microg. The first patient received 9 mg of bupivacaine. Supplemental anesthesia was provided through the epidural catheter if required. The primary outcome was successful analgesia, defined as a sensory block to at least T6, and no request for supplemental anesthesia. The ED95 for the satisfactory outcome was determined by a logistic model with non-log-transformed doses. Twenty-four normal weight and sixteen obese patients were enrolled. The estimated ED95 for all forty patients was 12.92 mg (95% CI: 11.49 to 34.77). The estimated ED95 for the normal weight and the obese subgroups were similar at 12.78 mg (95% CI: 10.75 to + infinity) and 11.86 mg (95%CI: 11.31 to 15.61), respectively. If single shot spinal anesthesia is used for cesarean delivery, obese and normal weight patients should receive similar doses of hyperbaric bupivacaine. Although in our study the effective dose 95% could not be precisely determined, it is possible to state that it is at least 11.49 mg.