Comparison of Vasopressor Boluses for Management of Hypotension After Spinal Anesthesia

In this study the investigators will compare the efficacy and side effects of two doses of norepinephrine bolus (6 mcg and 10 mcg) in management of maternal hypotensive episode after subarachnoid block during Cesarean delivery.

Maternal hypotension after subarachnoid block is a frequent and deleterious complication during cesarean delivery. Although prophylaxis against hypotension using vasopressors had become a standard recommendation; the incidence of hypotension is still ∼ 20% . Thus; management of maternal hypotension using vasopressor boluses is usually needed . The commonly used vasopressors during cesarean delivery are ephedrine, phenylephrine, and recently norepinephrine. The use of ephedrine is usually accompanied with maternal tachycardia and fetal acidosis. Phenylephrine had been the first line for prevention and management of maternal hypotension; however, its use might result in bradycardia and decreased maternal cardiac output . Norepinephrine is an alpha adrenergic agonist with weak beta adrenergic agonistic activity; thus, it does not cause significant cardiac depression as phenylephrine does. Norepinephrine was introduced for use during cesarean delivery with promising results . Few previous studies investigated the efficacy of Norepinephrine infusion for prevention of maternal hypotension. A dose-response study had investigated the best dose of Norepinephrine for prevention of maternal hypotension. In the aforementioned dose-response study, a dose of 6 mcg was reported as the best dose for prophylaxis against maternal hypotension. No studies had investigated the best bolus dose of norepinephrine for management of a maternal hypotensive episode. In this study the investigators will investigate the efficacy and side effects of two doses of norepinephrine bolus doses (6 mcg and 10 mcg) in management of maternal hypotensive episode after subarachnoid block during cesarean delivery.

Mothers in this group will receive a bolus of Norepinephrine 6 mcg for management of hypotensive episode after spinal anesthesia using Bupivacaine hydrochloride under prophylactic Norepinephrine infusion

Mothers in this group will receive a bolus of Norepinephrine 10 mcg for management of hypotensive episode after spinal anesthesia using Bupivacaine hydrochloride under prophylactic Norepinephrine infusion

An intravenous bolus of norepinephrine 6 mcg will be administered for management of maternal hypotension.

An intravenous bolus of norepinephrine 10 mcg will be administered for management of maternal hypotension.

Subarachnoid block will be performed using Bupivacaine hydrochloride (2.2 mL) in addition to fentanyl 25 mcg

number of patients with successful management of maternal hypotensive episode (defined as return of systolic blood pressure to be ≥ 80% of the baseline reading in the next reading 2 minutes after administration of norepinephrine bolus)

number of patients with successful management of maternal severe hypotensive episode (defined as systolic blood pressure lower than 60% of the baseline reading in the next reading 2 minutes after administration of norepinephrine bolus)

number of patients with reactive hypertension (defined as systolic blood pressure ≥120% from the baseline reading after administration of norepinephrine bolus)

the Apgar score of the fetus which range from 0 to 10. Th minimum value is 0 and the maximum value is 10. The worst value is 0 and the best value is 10

the measure of acidity or alkalinity of any solution on a logarithmic scale on which 7 is neutral, lower values are more acid and higher values more alkaline.

Inclusion Criteria: pregnant women scheduled for cesarean delivery Exclusion Criteria: patients with severe cardiac dysfunction patients with low blood pressure patients with ante-partum bleeding