Comparative Dose-Response Study of Phenylephrine Bolus for the Treatment of the First Episode of Spinal Anesthesia-Induced Hypotension for Cesarean Delivery in Severe Preeclamptic versus Normotensive Parturients

BACKGROUND: It is well-known that severe preeclamptic parturients have less vasopressor requirements than normotensive parturients; however, the exact dose difference is poorly documented. This study aimed to determine and compare the ED(50) and ED(90) of a single bolus phenylephrine for the treatment of spinal anesthesia-induced hypotension in parturients with severe preeclampsia and parturients with normotension. METHODS: Seventy-five parturients with severe preeclampsia scheduled for cesarean delivery under combined spinal-epidural anesthesia were enrolled and randomly allocated to receive a single bolus of phenylephrine at five different doses (40, 50, 60, 70, and 80 μg), whereas 75 parturients with normotension were randomized to receive a single bolus of phenylephrine at five different doses (70, 80, 90, 100, and 110 μg) for the treatment of the first episode of hypotension. Phenylephrine dose values were log-transformed, the proportions of the successful interventions at each dose were converted to probits, and regression analysis was performed. RESULTS: The ED(50) and ED(90) (95% CI) of bolus phenylephrine were 72.1 (61.7 to 79.9) μg and 107 (95.9–128.6) μg in parturients with normotension. The ED(50) and ED(90) values in parturients with severe preeclampsia were 47.6 (41.3–52.7) μg and 70.7 (62.9–86.7) μg. The relative median potency was 1.51 (1.16–2.61). CONCLUSION: Under this study conditions, severe preeclamptic parturients required a 34% reduction of ED(50) of phenylephrine dose compared with normotensive parturients.