Prophylactic Norepinephrine and Phenylephrine Boluses for Postspinal Anesthesia Hypotension

Prophylactic Norepinephrine and Phenylephrine Boluses for Postspinal Anesthesia Hypotension in Patients Undergoing Caesarean Section: A Randomized Sequential Allocation Dose-finding Study.

The purpose of this study is to investigate the potency between prophylactic norepinephrine and phenylephrine boluses for postspinal anesthesia hypotension in patients undergoing caesarean section.

Post-spinal anesthesia hypotension is a frequent complication during spinal anesthesia for cesarean section. The incidence of post-spinal anesthesia hypotension is as high as 62.1-89.7% if prophylactic measures are not taken. Vasopressor has been highly recommended for routine prevention and/or treatment of post-spinal anesthesia hypotension. As a potential substitute drug for phenylephrine, norepinephrine has gradually been used in parturients undergoing cesarean section. There's some evidence that prophylactic infusion of norepinephrine could effectively reduce the incidence of post-spinal anesthesia hypotension in parturients undergoing cesarean section. However, few studies had been indicated the ED50 (prevent postspinal hypotension in 50% of patients) and ED90 of prophylactic norepinephrine bolus and its potency compared to phenylephrine for postspinal anesthesia hypotension in patients undergoing caesarean section. The purpose of this study is to investigate the potency between prophylactic norepinephrine and phenylephrine boluses for postspinal anesthesia hypotension in patients undergoing caesarean section.

An initial prophylactic bolus dose of phenylephrine (37.5μg) simultaneous with spinal anesthesia. If the patient did not respond adequately to the current dose (SBP decreased to < 80% of baseline), the dose was considered to have failed and the subsequent dose for the following patient was increased to the next higher dose level. The dose administered to subsequent patients varied by increments or decrements of 12.5 μg according to the responses of previous patients according to the up-down sequential allocation.

An initial prophylactic bolus dose of norepinephrine (3μg) simultaneous with spinal anesthesia. The dose administered to subsequent patients varied by increments or decrements of 1 μg according to the responses of previous patients according to the up-down sequential allocation.

The dose that would be effective in preventing postspinal anesthesia hypotension in 50% (effective dose, ED 50) and 90% (ED90) of patients

Inclusion Criteria: 18-45 years Primipara or multipara Singleton pregnancy ≥37 weeks American Society of Anesthesiologists physical status classification I to II Scheduled for cesarean section under spinal anesthesia Exclusion Criteria: Body height < 150 cm Body weight > 100 kg or body mass index (BMI) ≥ 40 kg/m2 Eclampsia or chronic hypertension or baseline blood pressure ≥180 mmHg Hemoglobin < 7g/dl Fetal distress, or known fetal developmental anomaly