Comparison between two phenylephrine infusion rates with moderate co-loading for the prevention of spinal anaeshtesia-induced hypotension during elective caesarean section.

BACKGROUND: Phenylephrine induces maternal bradycardia in 50% of mothers when used for prevention and treatment of spinal anaesthesia-induced hypotension during caesarean delivery. Rapid fluid administration immediately after initiation of the spinal block (co-loading) may have a vasopressor sparing effect. The aim of this study was to evaluate the hypothesis that when using rapid crystalloid co-loading, an infusion of 50 mcg/minute of PE could be as effective as 100 mcg/minute in preventing maternal hypotension but with minimal maternal bradycardia and an acceptable fetal outcome.

METHODS: 117 mothers scheduled for elective caesarean section were recruited in this randomized controlled trial. Co-loading with 10 ml/kg of Hartmann's solution started immediately after a standard spinal anaesthesia. Parturients were then randomly allocated into two groups. Group 50 (n = 54) received phenylephrine infusion at 50 microg/min, and group 100 (n=63) 100 microg/min. Rescue phenylephrine boluses (50 mcg) were administered if needed to maintain systolic blood pressure between 80-100% of its baseline values.

RESULTS: Systolic blood pressure was not different between mothers in both groups during the study period. All neonatal Apgar scores at 1 minute were > or =7 and at 5 minutes were > or =9. No mother had umbilical arterial pH <7.2. Umbilical arterial and venous blood gas and acid base values were not different between both groups except the umbilical arterial PCO2 that was significantly higher in group 100. There were more frequent episodes of maternal bradycardia in Group 100 than in Group 50 (eleven and one parturients respectively). There was no difference in the incidence of nausea and vomiting in both groups.

CONCLUSION: In combination with rapid co-loading, an infusion rate of 50 microg/min of PE is as adequate as 100 microg/min in prevention of spinal anaesthesia-induced hypotension during elective caesarean section. Both infusions are associated with a similar neonatal outcome. PE infusion of 50 microg/min is associated with significantly less maternal bradycardia than 100 microg/min.