Determination of the 50% effective dose of sequential method for determining methoxamine with continued pumping and infusion to prevent hypotension during combined spinal epidural anesthesia

Abstract:

Objective：To determine the 50% effective dose（ED50） of methoxamine to prevent spinal-induced hypotension at elective cesarean delivery with constant-speed infusion. Methods：This was a prospective and double-blinded study. Forty-four pregnant women，with single fetus and full term，who were going to have cesarean delivery were included. The combined spinal epidural anesthesia was performed in the interspace of lumbus 3/4（L3～4）. When the spinal epidural anesthesia was completed，the methoxamine was infused at a rate of 100 mL/h，and the infusion was stopped after the baby was delivered. The initial concentration of methoxamine was 70 μg/mL and the constant speed was 100 mL/h. The targeted contractive blood pressure was maintained at the basic level and the sequential method was used to determine the drug concentration of next women，with concentration gradient of 1 μg/mL. Systolic blood pressure was lower than the base value was defined as ineffective concentration；systolic blood pressure was maintained the base value was defined as effective concentration. Probit regression was used to analyze the ED50 of methoxamine and 95% confidence index（CI）. Twenty pregnant women were collected in accordance with ED50，and the effective value of ED50 was calculated. Results：The ED50 of 100 mL/h methoxamine was 79.38 μg/mL（95%CI=76.59-112.48） and the effective value was 80%. The neonatal umbilical blood pH values were greater than 7.2. All neonatal Apgar scores at 1 min and 5 min were greater than 7. There was no side effects（nausea，vomiting，shivering，bradycardia and so on） in patients with effective blood pressure control. Conclusion：The ED50 of 100 mL/h methox－amine to prevent hypotension under spinal anesthesia during caesarean section is 79.38 μg/mL（95%CI=76.59-112.48）.