Effect of Different Phenylephrine Bolus Doses for Treatment of Hypotension during Spinal Anaesthesia in Patients Undergoing Elective Caesarean Section

The efficacy of phenylephrine might be improved by giving doses higher than that traditionally used (100 μg). This study compared the effects of three initial bolus doses of intravenous phenylephrine; 100 μg (group P100), 125 μg (group P125) and 150 μg (group P150), for the treatment of post-spinal hypotension in patients undergoing elective caesarean delivery. If hypotension was not corrected by this dose, additional boluses of 25 μg were given every minute. Further hypotensive episodes were treated with half the initial bolus dose, followed by 25 μg boluses, as required. Umbilical arterial and venous blood samples were obtained for blood gas analysis and Apgar scores recorded. One hundred and twenty subjects (40 per group) who developed post-spinal hypotension (75%) were included in this randomised, double blind trial. Although systolic blood pressure was higher at certain time-points after 150 μg phenylephrine, there were no statistically significant differences in the effectiveness of the first bolus of phenylephrine to treat hypotension (85%, 95% and 95% in groups P100, P125 and P150, respectively, P=0.215); the additional dose of phenylephrine after the first bolus ( P=0.810); the number of additional boluses ( P=0.318) or of hypotensive episodes ( P=0.118). There were no significant differences in the number of patients developing reactive hypertension or bradycardia, in maternal side-effects or in neonatal outcomes. Although the study may have been underpowered, initial phenylephrine bolus doses of 100 μg, 125 μg and 150 μg did not significantly differ in efficacy to treat post-spinal hypotension in these patients.