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

Abstract

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.