To Observe The Effects Of Norepinephrine And Phenylephrine On Placental Vascular Resistance During Cesarean Section Under Spinal Anesthesia Via Ultrasonography

Background:The prevention and treatment of maternal hypotension during spinal anesthesia for cesarean delivery has been one of the central issues in Obstetric anesthesia since the 1970 s.A decrease of systemic vascular resistance has been recognized as a significant contributor.Accordingly,phenylephrine(a pure ?-adrenergic receptor agonist) is the currently recommended first-line vasopressor used to treat maternal hypotension in guidelines.However,Phenylephrine can cause reflexive decreases in maternal heart rate and cardiac output via baroreceptor.Norepinephrine has weak ?-adrenergic receptor agonist activity in addition to potent ?-adrenergic receptor activity and therefore may be suitable for maintaining blood pressure with less negative inotropic effects compared with phenylephrine.Since 2015,various studies have explored the use of norepinephrine in Obstetric anesthesia.However,the effect of norepinephrine on placental vascular resistance has not been evaluated.Objective : To preventing and treating hypotension with norepinephrine or phenylephrine during cesarean section under spinal anesthesia while to observe the changes of placental vascular resistance via color Doppler ultrasonography.Methods:Sixty female subjects were randomly divided into two groups to receive norepinephrine(8?g/ml,0.3ml/Kg/h) or phenylephrine(100?g/ml,0.3ml/Kg/h),Doppler ultrasonography was used to measure resistance index(RI) and systolic peak velocity/diastolic velocity(S/D) of umbilical artery at each time point(T0: prior to administration of anesthesia,T1: 10 min after intrathecal injection).Results:Data of RI and S/D values in two groups remained within the normal range.The RI and S/D values of umbilical artery slightly decreased at T1 point in norepinephrine group,whereas slightly increased in phenylephrine group.Conclusions:Norepinephrine and phenylephrine are both safety drug in obstetric anesthesia.Norepinephrine is more beneficial for placental perfusion,maybe more suitable for pathological placental perfusion(such as preeclampsia).