Data regarding the optimum dose of norepinephrine for management of severe maternal hypotension is lacking. A previous report showed that the use of 10-mcg norepinephrine bolus was not superior to the 5-mcg bolus in the management of severe hypotension in addition the incidence of reactive bradycardia and hypertension was comparable in the two doses. Therefore, we hypothesize that using a higher dose of norepinephrine (15 mcg) would increase the success rate of management of severe hypotensive episode.

Upon arrival to the operating room, the patient will be in supine position with left uterine displacement using a wedge below the right buttock. Routine monitoring will be applied (electrocardiography, pulse oximetry, and non-invasive blood pressure monitor). An 18G-cannula will be inserted, and the patients will receive 10 mg metoclopramide. Baseline heart rate and systolic blood pressure will be recorded as the average of three consecutive readings with 2-minutes interval.

Lactated Ringer's solution will be infused at rate of 15 mL/Kg over 10 minutes as a co-load; spinal anesthesia will be achieved by injecting 10 mg of hyperbaric bupivacaine and 20 mcg fentanyl into the subarachnoid space at L3-L4 or L4-L5 interspace using 25G spinal needle.

After subarachnoid block, mothers will be placed in the supine position with left-lateral tilt.

Block success will be assessed after 5 minutes from intrathecal injection of local anesthetic; and will be confirmed if sensory block level is at T4.

The patient would receive the study drug only if she developed severe post-spinal hypotension (defined as systolic blood pressure ≤60% of the baseline reading) as her first hypotensive episode. The management of the hypotensive episode will be considered successful if the systolic blood pressure is > 80% of the baseline within 2 mins of the bolus. If the bolus failed, norepinephrine bolus of 5 mcg will be given.

Any other hypotensive episode (systolic blood pressure <80% of baseline) will be managed with norepinephrine bolus of 5 mcg.

Intraoperative bradycardia (defined as heart rate less than 55 bpm) will be managed by IV atropine bolus (0.5 mg) will be administered.

Fluid administration will be continued up to a maximum of 1.5 liters. An oxytocin bolus (1 IU) will be delivered over five seconds after delivery then infused at a rate of 2.5-7.5 IU/hour.

Inclusion Criteria:

• full-term singleton pregnant women
• American society of anesthesiologist II, scheduled for elective cesarean delivery,

Exclusion Criteria:

• Patients with uncontrolled cardiac morbidities (patients with tight valvular lesion, impaired contractility with ejection fraction < 50%, heart block, and arrhythmias),
• hypertensive disorders of pregnancy,
• peripartum bleeding,
• coagulation disorders (patients with INR >1.4 and or platelet count < 80000 /dL) or any contraindication to regional anesthesia,
• baseline systolic blood pressure (SBP) < 100 mmHg

The datasets used and/or analyzed during the current study are available from the corresponding author upon reasonable request