Application Of Norepinephrine On Hypotension During Spinal Anesthesia For Cesarean Section

Background:Hypotension is one of the most common complications during spinal anesthesia for cesarean section.The incidence can reach as high as 70%.Hypotension could not only cause nausea and vomiting,maternal placental abruption,circulation failure,and even cardiac arrest and death on mother,but also lead to fetal hypoxia,acidosis,respiratory distress,neonatal asphyxia,and even the central nervous system damage on the fetus.Phenylephrine is the first-line choice for prevention and treatment of hypotension during spinal anesthesia for cesarean section.But in our clinical practice,we have found that phenylephrine could cause reflex bradycardia,which required atropine treatment.Moreover,phenylephrine is not effective in some patients,and we have to choose other vasopressors to treat spinal hypotension.Recent research found that compared with phenylephrine,norepinephrine was effective for preventing spinal hypotension and was associated with greater heart rate and cardiac output by computer-controlled infusion during spinal anesthesia for cesarean sectionPart one:Comparison of prophylactic bolus norepinephrine and phenylephrine on hypotension during spinal anesthesia for cesarean sectionObjectives:This study compared the effects of prophylactic bolus norepinephrine and phenylephrine on hypotension during spinal anesthesia for cesarean section.Methods:A total of 132 healthy parturients having cesarean section under spinal anesthesia were enrolled in this prospective,randomized,double-blinded,parallel-group trial.The inclusion criteria were:ASA(American Society of Anesthesiologists)physical status 1 to 2,singleton term pregnancy,and scheduled for elective cesarean section under spinal anesthesia.Exclusion criteria were:age less than 18 year,height less than 150 cm or more than 180 cm,weight less than 50 kg or more than 100 kg,contraindications to spinal anesthesia,allergy to drugs used in the study,preeclampsia,placenta praevia,diabetes mellitus,hypertension,or cardiovascular disease.Patients were randomized to receive prophylactic bolus norepinephrine(10 μg)or phenylephrine(50 μg)immediately after spinal anesthesia.The primary outcome compared was incidence of bradycardia(defined as heart rate<60 beats/min).The secondary outcomes were blood pressure,heart rate,cardiac output,nausea and vomiting,and neonatal outcome.Results:The incidence of bradycardia was significantly lower in the norepinephrine group(2%)compared with that in the phenylephrine group(13%,P<0.05).The incidence of bradycardia was significantly lower in the norepinephrine group(2%)compared with that in the phenylephrine group(13%,P<0.05).Five patients had heart rate lower than 55 beats/min and needed atropine 0.5 mg administration in the phenylephrine group.Cardiac output at 5 min was significantly greater in the norepinephrine group than that in the phenylephrine group(P<0.05).From induction until delivery,there were no significant differences in systolic blood pressure.Neonatal outcome was similar between groups.Conclusions:Norepinephrine is as effective as phenylephrine in preventing spinal hypotension but has less adverse effects on heart rate and greater cardiac output compared with phenylephrine during caesarean section.Part two:Effect of prophylactic bolus norepinephrine on hypotension during spinal anesthesia for cesarean sectionObjectives:This study was planned to compared the effects of two different bolus doses of intravenous norepinephrine on hypotension during spinal anesthesia for cesarean section.Methods:In a prospective,randomized,double-blinded,clinical study,116 healthy parturients having cesarean section under spinal anesthesia were randomized to receive prophylactic bolus norepinephrine 10μg(group N1)and 15μg(group N2)immediately after spinal anesthesia.The inclusion criteria were:ASA(American Society of Anesthesiologists)physical status 1 to 2,singleton term pregnancy,and scheduled for elective cesarean section under spinal anesthesia.Exclusion criteria were:age less than 18 year,height less than 150 cm or more than 180 cm,weight less than 50 kg or more than 100 kg,contraindications to spinal anesthesia,allergy to drugs used in the study,preeclampsia,placenta praevia,diabetes mellitus,hypertension,or cardiovascular disease.The primary outcome compared was incidence of hypertension(defined as SBP>120%of baseline)and bradycardia(defined as heart rate<60 beats/min).The secondary outcomes were blood pressure,heart rate,nausea and vomiting,and neonatal outcome.Results:The incidence of hypertension was significantly lower in the group N1(3%)compared with that in the group N2(14%,P<0.05).The incidence of bradycardia was significantly lower in the group N1(3%)compared with that in the group N2(16%,P<0.05).Six patients had heart rate lower than 55 beats/min and needed atropine 0.5 mg administration in the group N2.Systolic blood pressure at 2 min was significantly higher in the group N2 than that in the group N1(P<0.05).Heart rate at 2 min and 4 min was significantly lower in the group N2 than that in the group N1(P<0.05).Neonatal outcome was similar between groups.Conclusions:10μg norepinephrine is more safe and effective in preventing spinal hypotension but has less adverse effects on hypertension and bradycardia during caesarean section.