ED50 of hyperbaric bupivacaine with fentanyl for cesarean delivery under combined spinal epidural in normotensive and preeclamptic patients.

BACKGROUND AND OBJECTIVES: The use of reduced intrathecal doses is advised for spinal anesthesia during cesarean delivery. However, there are inadequate data regarding the minimum effective dose of intrathecal bupivacaine for cesarean delivery. Preeclampsia is caused by an endothelial dysfunction leading to generalized vasoconstriction. Whether this can offset the pregnancy-induced decrease in intrathecal dose requirement caused by epidural venous dilation and consequent thecal compression is not known. There are no data to evaluate the minimum effective dose of intrathecal drug for cesarean delivery in preeclamptic patients. This study aimed to determine the minimum effective dose represented by the ED50 of intrathecal hyperbaric bupivacaine for normotensive and severely preeclamptic patients undergoing elective cesarean delivery.

METHODS: Combined spinal epidural anesthesia was administered using a standardized technique on 18 consecutively preeclamptic and normotensive patients, each carrying an otherwise uncomplicated singleton pregnancy. The dose of intrathecal hyperbaric bupivacaine was decided by using the up-and-down method with an initial dose of 9 mg and dosing change of 1 mg. All patients received 20 μg of fentanyl intrathecally with bupivacaine. A successful block was defined as one that resulted in a sensory block to T4 level with modified Bromage score of 1 or 2 within 15 minutes of intrathecal injection.

RESULTS: ED50 of intrathecal hyperbaric bupivacaine was identical in severely preeclamptic and normotensive parturients undergoing elective cesarean delivery (4.7 mg; 95% confidence interval, 4.5-4.9 mg).

CONCLUSIONS: When a combined-spinal epidural is planned in normotensive or severely preeclamptic patients for an elective cesarean delivery, the ED50 of intrathecal hyperbaric bupivacaine along with 20 μg of fentanyl is 4.7 mg.