Dose-effect relationship of norepinephrine in treatment of hypotension after spinal anesthesia in cesarean section / 中华麻醉学杂志

ABSTRACT

Objective:To determine the dose-effect relationship of norepinephrine in the treatment of hypotension after spinal anesthesia in cesarean section.Methods:Ninety American Society of Anesthesiologists physical status Ⅰ or Ⅱ parturients who were at full term with a singleton fetus, body mass index of 20-35 kg/m 2, blood pressure 100-140 mmHg, heart rate 60-100 beats/min, scheduled for elective cesarean section, were divided into 6 different doses of norepinephrine groups (NE2, NE4, NE6, NE8, NE10 and NE12 groups) using a random number table method, with 15 cases in each group.The maternal basal systolic blood pressure was measured after entering the operating room.Anesthesia was performed by injecting hyperbaric bupivacaine 9 mg into the subarachnoid space over 45 s. When hypotension occurred for the first time after anesthesia (systolic blood pressure was lower than 80% of the baseline value), norepinephrine 2, 4, 6, 8, 10 and 12 μg (diluted to 5 ml in normal saline) were intravenously injected in NE2, NE4, NE6, NE8, NE10 and NE12 groups, respectively.Systolic blood pressure was measured at 60 s after completion of injection.The effective treatment of hypotension was defined as the recovery of systolic blood pressure to more than 80% of the baseline value.The logistic regression analysis method was used to draw the dose-effect curve of norepinephrine in treating hypotension after spinal anesthesia in cesarean section.The median effective dose (ED 50), 95% effective dose (ED 95) and 95% confidence interval (CI) were calculated.The time to first hypotension, effective treatment of hypotension, and occurrence of bradycardia and nausea and vomiting after intravenous injection of norepinephrine were recorded.The Apgar scores of the neonates at 1 and 5 min after birth were recorded.The umbilical artery blood samples of neonates were collected immediately after cutting the cord for blood gas analysis. Results:There was no significant difference in the incidence of maternal basal systolic blood pressure, time to first hypotension, bradycardia, and nausea and vomiting among the six groups ( P>0.05). The rate of effective treatment of hypotension increased with the increase of the dose in the six groups ( P<0.05). There was no significant difference in Apgar score and indexes of umbilical artery blood gas analysis at 1 and 5 min after birth among the six groups ( P>0.05). The ED 50 (95% CI) of norepinephrine in the treatment of hypotension after spinal anesthesia in cesarean section was 4.0 (3.0 to 5.0) μg, and the ED 95 (95% CI) was 11.8 (8.9-20.4) μg. Conclusion:The ED 50 and ED 95 of norepinephrine are 4.0 and 11.8 μg, respectively, when used for treating hypotension after spinal anesthesia in cesarean section.