Comparison of phenylephrine infusion regimens for maintaining maternal blood pressure during spinal anaesthesia for Caesarean section †

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Abstract
Background. During spinal anaesthesia for Caesarean section, the optimal phenylephrine regimen and the optimal blood pressure (BP) to which it should be titrated are undetermined. The ideal regimen would balance efficacy for maintaining uteroplacental perfusion pressure against potential for uteroplacental vasoconstriction, both of which may affect fetal acid–base status. We compared phenylephrine infusion regimens based on three different BP thresholds. Methods. After intrathecal injection, we infused phenylephrine 100 µg min–1 for 2 min. Then, until delivery, we infused phenylephrine whenever systolic BP (SBP), measured every 1 min, was below a randomly assigned percentage of baseline: 100% (Group 100, n=25), 90% (Group 90, n=25) or 80% (Group 80, n=24). We compared umbilical blood gases, Apgar scores and maternal haemodynamics and symptoms. Results. Patients in Group 100 had fewer episodes [median 0 (range 0–8)] of hypotension (SBP PP=0.034). No patient had umbilical arterial pH P=0.006). Conclusions. For optimal management, phenylephrine should be titrated to maintain maternal BP at near‐baseline values. Br J Anaesth 2004; 92: 469–74

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