This is a Study That Aims to Estimate the Effect of Maternal Body Mass Index on the Prophylactic Dose of Norepinephrine Infusion for Preventing Hypotension in Parturient After Spinal Anesthesia

This is a randomized, double-blinded controlled study that aims to estimate the effect of maternal body mass index on the prophylactic dose of norepinephrine infusion for preventing hypotension in parturient after spinal anesthesia.

Routine preoperative investigations will be done to all patients including laboratory investigations as (complete blood picture, prothrombin time and partial thromboplastin time), age and BMI will be recorded.

All the patients will be fasting for solid food for 6-8 hours and for clear fluids for 4 hours before surgery.

Upon entry into the operating theater, all patients will be placed under standard American Society of Anesthesiologist (ASA) monitoring including 5-lead electrocardiography, pulse oximetry and non-invasive blood pressure. Baseline values of systolic blood pressure (SBP), diastolic blood pressure (DBP), heart rate (HR) and mean blood pressure (MBP) will be measured in supine position with left uterine displacement (15 degree wedge under the right buttock) and recorded as the arithmetic mean of three consecutive measurements at least 2 min intervals with a difference of less than 10%.

As per standard practice, SBP, DBP, MBP, HR and pulse oximetry measurements will be recorded in every 2 min throughout the surgery. An 18-gauge cannula will be inserted into a large vein, The patients will receive no premedication. The study period will be the interval between the initiation of spinal injection and delivery of the fetus .

Subarachnoid block will be performed through L3-4 or L4-5 intervertebral space in the sitting position. A solution of 12.5 mg 0.5% hyperbaric bupivacaine plus 25 mic fentanyl will be injected into subarachnoid space using a 25-gauge pencil point spinal needle. After completion of subarachnoid injection, patients will be immediately placed supine on the operating table with left uterine displacement using a 15° wedge .

The highest level of sensory blockade will be assessed using a sterile needle, surgery will be permitted after a bilateral T6 sensory block .

To assure blinding, the study group will be known only to the research assistant, who would be responsible for each step of the NE administration including starting dose of NE infusion, applying a bolus dose or cessation of the infusion of NE according to the study protocol .

Immediately after the injection of the spinal anesthetic, patients will have a norepinephrine protocol corresponding to the randomized group. The study drug will be started intravenously at a rate of 50 ml/h, Lactated Ringer's solution warmed at 37°C will also administered, starting with a loading dose of 10 ml/kg given rapidly over 15 minutes and will then be adjusted to a slow maintenance flow rate to keep the vein open .

After delivery, an intravenous infusion of oxytocin (20 IU) will be slowly administered. After the end of surgery, the mother will be transported to the recovery room with routine monitoring .

NE infusion will be stopped 5 min after delivery in all patients . The intraoperative period will be divided into 2 consecutive periods . The first period is called the post-spinal period and will include the period between the completion of subarachnoid block and the time of delivery.

The subsequent period between the time of delivery and the end of the surgery will be called the post-delivery period.

All complications will be entitled according to the period in which they occurred. Accordingly, post spinal hypotension (PSH) and post delivery hypotension (PDH) will be defined as a reduction in SBP of 20% or more of the baseline value before and after the delivery, respectively .

Similarly, post-spinal severe hypotension (PSSH) and post-delivery severe hypotension (PDSH) will be defined as a decrease in SBP of 40% or more from the baseline value before and after the delivery respectively.

Management of complications: .

1. If PSH or PDH was developed, a bolus of 10 mg ephedrine will be administered.
2. If hypotension persisted after 2 min, a repeated dose of 10 mg ephedrine i.v. will be administered again.
3. If PSSH or PDSH occurred, 15 mg ephedrine i.v. bolus will administered.
4. In case of bradycardia (heart rate less than 60 beats per min ) without maternal hypotension, NE infusion will be stopped.
5. If bradycardia persists for 2 min despite discontinuation of NE infusion, 0.5 mg of atropine i.v. bolus will be administered.
6. Moreover, if the heart rate falls below 50 beats per min , 0.5 mg atropine i.v. bolus will be administered without waiting for 2 min. As soon as the HR increases above 60 beats per min, NE infusion will be started again at the same infusion dose corresponding to the NE group that the patient is randomized.
7. If bradycardia is accompanied by hypotension, 10 mg ephedrine i.v. bolus will be administered.
8. In contrast to hypotension, if the SBP is found to be 20% above the basal value, the NE infusion will be stopped and recorded as a hypertensive episode. If the systolic blood pressure falls below this determined hypertensive value, NE will be restarted at the same dose.
9. Incidence of maternal complication as nausea and vomiting will be recorded and treated with granitryl (1 mg IV) Apgar score after delivery. Apgar score at 1 and 5 min will be recorded after delivery by the attending pediatric physician.

Hemodynamic changes mentioned above and the number of interventions including administration of ephedrine or atropine, stopping or re-starting of NE infusion, which will be applied by the physician to overcome the hemodynamic consequences of spinal anesthesia will all be recorded until the patient leaves the operating room.