Norepinephrine or Phenylephrine in Bolus for Hypotension in Cesarean Delivery

This is a prospective, randomized, double-blind, comparative two-group clinical study to observe two vasopressor drugs, phenylephrine and noradrenaline, in the ability to maintain systemic arterial pressure in pregnant women after spinal anesthesia for cesarean section; based on the hypothesis that, since noradrenaline has a predominant alpha-adrenergic action and a weak 1- beta-adrenergic beta action, it could be as capable of maintaining blood pressure effectively as phenylephrine, but with a lower frequency of bradycardia; patients who meet the inclusion criteria will be randomly assigned to one of the groups to be studied: group F - phenylephrine at a dose of 100mcg bolus and N - noradrenaline at the dose of 5mcg. One of these drugs will be used whenever systolic blood pressure drops below 10% of the baseline, additional doses will be allowed whenever necessary, aiming at maintaining the systolic blood pressure at baseline values; the blood pressure will be measured non-invasively and the heart rate by pulse oximeter and electrocardiogram.

Inclusion criteria

• Pregnant women, with single gestation, with cesarean programming to be performed under spinal anesthesia;
• Age above 18 years;
• Physical State American Society of Anesthesiologists (ASA) II and III;
• Weight between 50kg and 120kg;
• Height between 140cm and 180cm.

Exclusion criteria

• Refusal to participate in the study;
• Pregnant women with fetus with known abnormalities;
• Pregnant women with cardiovascular disease;
• Pregnant women with pregnancy-specific hypertensive disease;
• Allergy to any medication to be used in the study;
• Users of monoamine oxidase inhibitors;
• Users of tricyclic antidepressants;
• Emergency caesarean section due to acute fetal distress;
• Situations in which the sensory level after single intrathecal injection of the local anesthetic does not reach at least T6 within 5 minutes after spinal anesthesia.