Comparison of metaraminol, phenylephrine and ephedrine in prophylaxis and treatment of hypotension in cesarean section under spinal anesthesia

Abstract

Maternal hypotension is a common complication after spinal anesthesia for cesarean section, with deleterious effects on the fetus and mother. Among the strategies aimed at minimizing the effects of hypotension, vasopressor administration is the most efficient. The aim of this study was to compare the efficacy of phenylephrine, metaraminol, and ephedrine in the prevention and treatment of hypotension after spinal anesthesia for cesarean section. Ninety pregnant women, not in labor, undergoing cesarean section were randomized into three groups to receive a bolus followed by continuous infusion of vasopressor as follows: phenylephrine group (50 g + 50 g/min); metaraminol group (0.25 mg + 0.25 mg/min); ephedrine group (4 mg + 4 mg/min). Infusion dose was doubled when systolic blood pressure decreased to 80% of baseline and a bolus was given when systolic blood pressure decreased below 80%. The infusion dose was divided in half when systolic blood pressure increased to 120% and was stopped when it became higher. The incidence of hypotension, nausea and vomiting, reactive hypertension, bradycardia, tachycardia, Apgar scores, and arterial cord blood gases were assessed at the 1st and 5th minutes.There was no difference in the incidence of hypotension, bradycardia, reactive hypertension, infusion discontinuation, atropine administration or Apgar scores. Rescue boluses were higher only in the ephedrine group compared to metaraminol group. The incidence of nausea and vomiting and fetal acidosis were greater in the ephedrine group. The three drugs were effective in preventing hypotension; however, fetal effects were more frequent in the ephedrine group, although transient. Avaliação comparativa entre metaraminol, fenilefrina e efedrina na profilaxia e no tratamento da hipotensão em cesarianas sob raquianestesiaResumo Hipotensão materna é uma complicação comum após raquianestesia em cirurgia cesariana, trazendo efeitos deletérios para o feto e a mãe. Entre as estratégias com o objetivo de minimizar os efeitos da hipotensão, a administração de vasopressores é a mais eficiente. O objetivo deste estudo foi comparar a eficácia da fenilefrina, metaraminol e efedrina na prevenção e tratamento de hipotensão após raquianestesia em cirurgia cesariana. Noventa gestantes que não estavam em trabalho de parto submetidas à cesariana eletiva foram randomizadas em três grupos para receber um bolus, seguido de infusão contínua de vasopressor da seguinte forma: Grupo Fenilefrina (50 g + 50 g/min); Grupo Metaraminol (0,25 mg + 0,25 mg/min); Grupo Efedrina (4 mg + 4 mg/min). A dose da infusão foi dobrada quando a pressão arterial sistólica (PAS) decresceu até 80% dos valores basais e um bolus foi dado quando a PAS decresceu para valores abaixo de 80%. A dose da infusão foi dividida ao meio quando a PAS aumentou até 120% e foi interrompida quando mais elevada. Foram analisadas as incidências de hipotensão, náuseas e vômitos, hipertensão reativa, bradicardia, taquicardia e escores de Apgar no primeiro e quinto minutos e gases de sangue arterial d...

A randomised double‐blind trial of phenylephrine and metaraminol infusions for prevention of hypotension during spinal and combined spinal–epidural anaesthesia for elective caesarean section

“…Possibly due to unidentified confounders, both the umbilical artery and vein pH values were of lower magnitude than those found in our study. However, our results were consistent with those of Aragao et al , who compared the same three drugs in 90 women. They used a bolus before an infusion, with initial infusion rates for phenylephrine and metaraminol identical to those in our study.…”

“…Cardiac output and heart rate are closely linked, so despite a lack of evidence of differences in outcomes , avoidance of bradycardia is also thought to be an important management aim . We found that the groups did not differ significantly with respect to the incidence of bradycardia or the lowest maternal heart rate, as did similar comparative studies .…”

“…In a clinical trial it was superior to ephedrine in maintaining maternal systolic arterial pressure and neonatal umbilical artery pH . Two previous studies have also compared metaraminol and phenylephrine . In a small study on elective caesarean section involving women of unspecified gestation, Bhardwaj et al evaluated these drugs in a three‐way comparison that included ephedrine.…”

“…They used a bolus before an infusion, with initial infusion rates for phenylephrine and metaraminol identical to those in our study. These investigators found no between‐group differences with respect to neonatal outcomes or maternal haemodynamic status; however, their primary outcome was not clearly defined and no sample size calculation was performed .…”

“…Maintaining maternal blood pressure and heart rate, a surrogate marker of cardiac output, close to baseline are the usual primary goals of vasopressor prophylaxis . The administration of drugs, other than ephedrine, with combined α‐ and β‐adrenergic receptor agonist activity has been described, including noradrenaline and metaraminol . Metaraminol appears to have advantages over ephedrine , but there are few direct comparisons with phenylephrine, despite its long‐standing use in non‐obstetric practice .…”