Epinephrine Infusion for Prophylaxis Against Maternal Hypotension During Cesarean Delivery

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 supine position with left-lateral tilt and the vasopressor infusion will be started.

• 0.01 mcg group
• 0.02 mcg group
• 0.03 mcg group The vasopressor infusion will be through the same line as the fluid a three-way stopcock. The vasopressor infusion will be stopped if heart rate became ≥130% of baseline or systolic blood pressure ≥120% of baseline, otherwise the infusion will be stopped 5 minutes after delivery of the baby.

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.

Post-spinal hypotension (defined as systolic blood pressure ≤80% of the baseline reading during the period from intrathecal injection to delivery of the fetus) will be managed by administration of 9 mg of ephedrine Severe post-spinal hypotension (defined as systolic blood pressure ≤60% of the baseline reading during the period from intrathecal injection to delivery of the fetus) will be managed by administration IV ephedrine 15 mg.

Reactive hypertension (defined as systolic blood pressure ≥120% of the baseline reading) will be managed by stoppage of the infusion till the next systolic blood pressure reading. The infusion will be then re-started at the half of the initial rate, when systolic blood pressure decreases to be within 20% of the baseline reading.

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 (0.5 IU) will be delivered over five seconds after delivery the infused at a rate of 2.5 IU/hour.