Comparative evaluation of two doses of phenylephrine infusion to prevent intra-operative nausea and vomiting during elective obstetric spinal anesthesia

Background and Aims: Hypotension is very common after obstetric spinal anesthesia. Maternal hypotension in turn leads to intra-operative nausea and/or vomiting (IONV). We planned this study to compare the effect of phenylephrine infusion of 25 μg/min and 50 μg/min for preventing IONV in patients undergoing elective lower segment cesarean section. Material and Methods: This prospective double-blind randomized placebo controlled trial was conducted on 195 parturients with singleton pregnancy undergoing elective cesarean section under subarachnoid block. Parturients were randomly allocated into three groups, groups C, P25, and P50, to receive normal saline at 15 ml/hour, 100 μg/ml phenylephrine as 15 ml/hour infusion (dose 25 μg/min), and 200 μg/ml phenylephrine as 15 ml/hour infusion (dose 50 μg/min), respectively. Groups were compared with regard to incidence of IONV, rescue mephentermin consumption, hemodynamic parameters, neonatal outcome, and adverse effects. Categorical data were presented as number and compared using Chi-square test. Continuous variables were presented as mean ± SD and compared using t-test or ANOVA. P < 0.05 was considered statistically significant. Results: Group PE50 experienced a significantly lesser number of episodes of IONV compared to group PE25 and group C (0.09 ± 0.29 versus 0.23 ± 0.42 and 0.55 ± 0.84, respectively; P < 0.05). Group PE50 also required a significantly lesser number of rescue mephentermine for hypotension when compared to groups PE25 and C (0.00 v/s 0.18 ± 1.04 v/s 3.13 ± 5.31, P < 0.001). No significant difference was observed in number of patients experiencing IONV between the three groups (32% in PE50, 23% in PE25, 9% in C). Conclusion: Infusion of 50 microgram/min phenylephrine is superior to 25 microgram/min infusion and placebo to control IONV with significantly reduced cumulative rescue vasopressor consumption in patients undergoing elective cesarean section under subarachnoid block (SAB).