Estimation of the Effective Dose of Phenylephrine Infusion for Preventing Spinal Anesthesia-Induced Hypotension in...

Spinal anesthesia for cesarean delivery may be associated with hypotension and fetal acidosis. Phenylephrine, an α1 adrenergic receptor agonist, is effective in treating hypotension with the benefit of less placental transfer.

The objective of this study was to determine the optimum dose of prophylactic phenylephrine infusion for preventing spinal anesthesia-induced hypotension in women undergoing elective cesarean delivery and to assess its effect on fetal outcomes, as measured by APGAR scores at 1, 5, and 10 minutes.

Two hundred and forty patients were included in this double-blinded study. Women undergoing elective cesarean section were preloaded with crystalloids and then randomly allocated to receive prophylactic Phenylephrine infusion at either 25, 50, 75, or 100 µg/minute immediately after spinal anesthesia (Groups A, B, C, and D, respectively). Maternal hemodynamic parameters, total dose of phenylephrine used, APGAR score, and incidence of maternal complications like reactive hypertension, bradycardia, nausea, and vomiting, as well as fetal complications like fetal acidosis, were noted. The study was registered with the Clinical Trials Registry of India (CTRI/2019/07/020231, dated July 17, 2019) Results: Demographic parameters were comparable across all four groups (P > 0.05). The incidence of maternal hypotension was lowest in Group B (50 µg/minute) at 15.0%, compared to 41.7% in Group A, 30.0% in Group C, and 23.3% in Group D (P = 0.001). Maternal adverse events such as nausea/vomiting occurred in 5% of Group B, 28.3% of Group A, 31.7% of Group C, and 20% of Group D (P = 0.016). Mean phenylephrine requirements were 692 ± 67 µg (Group A), 1,269 ± 120 µg (Group B), 592 ± 115 µg (Group C), and 439 ± 83 µg (Group D) (P < 0.001). Mean APGAR scores at 1 minute were above 8.4 for all groups; all neonates had mean APGAR scores above 9.8 by 5 minutes (P > 0.05). Maternal complications such as bradycardia ranged from 25% to 63% across groups. The frequency of bradycardia was significantly higher in Groups C (63.3%) and D (60%) than in Groups A (26.7%) and B (25%) (P < 0.001). The 95% confidence intervals for major outcomes indicated statistical significance for these comparisons.

We concluded that starting prophylactic Phenylephrine infusion at 50 µg/minute immediately after spinal anesthesia was an effective and simple method of reducing the incidence, frequency, and magnitude of hypotension in elective cesarean section with no adverse effect on neonatal outcome.