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 ED₅₀ and ED₉₀ 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 ED₅₀ and ED₉₀ (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 ED₅₀ and ED₉₀ 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 ED₅₀ of phenylephrine dose compared with normotensive parturients.
Keywords: cesarean delivery, spinal anesthesia, hypotension, phenylephrine, preeclampsia