The Potency of Prophylactic Norepinephrine and Phenylephrine Boluses for Postspinal Anesthesia Hypotension

The Potency of Prophylactic Norepinephrine and Phenylephrine Boluses for Postspinal Anesthesia Hypotension

Comparison of the Potency of Prophylactic Norepinephrine and Phenylephrine Boluses for Postspinal Anesthesia Hypotension in Patients With Severe Preeclampsia During Caesarean Section

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

Preeclampsia, which affects 5% to 7% of patients, is a significant cause of maternal and neonatal morbidity and mortality. Because of constricted myometrial spiral arteries with exaggerated vasomotor responsiveness, though blood pressure in patients with preeclampsia are apparently higher than healthy patients, placental hypoperfusion is more common. Spinal anesthesia is still the preferred mode of anesthesia in patients with preeclampsia for cesarean section. In preeclampsia patients, spinal anesthesia improve intervillous blood flow (provided that hypotension is avoided) which contribute to increase placental perfusion. Even so, 17-26% patients with preeclampsia experienced postspinal anesthesia hypotension due to the extensive sympathetic block that occurred with spinal anesthesia. As a potential substitute drug for phenylephrine and ephedrine, norepinephrine has gained traction for use in patients undergoing cesarean section. However, the ED50 (prevent postspinal hypotension in 50% of patients) and ED90 of prophylactic norepinephrine bolus is still unknown. The purpose of this study is to investigate the potency between prophylactic norepinephrine and phenylephrine boluses for postspinal anesthesia hypotension in patients with severe preeclampsia during 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 ≥32 weeks American Society of Anesthesiologists physical status classification II to III Scheduled for cesarean section under spinal anesthesia Exclusion Criteria: Baseline blood pressure ≥180 mmHg Body height < 150 cm Body weight > 100 kg or body mass index (BMI) ≥ 40 kg/m2 Eclampsia or chronic hypertension Hemoglobin < 7g/dl Fetal distress, or known fetal developmental anomaly