Influence of prophylactic phenylephrine infusion on dose requirements of intrathecal hyperbaric bupivacaine during spinal anesthesia in cesarean sections: a pilot study

Background: Phenylephrine has been widely used in C-sections. However, it has been reported to decrease the spread of intrathecal local anesthetics. This present study aimed to observe the effects of prophylactic phenylephrine infusion on dose requirements of intrathecal hyperbaric bupivacaine during spinal anesthesia in cesarean sections. Methods: Based on receiving or not receiving phenylephrine infusion, fifty patients were enrolled and allocated into Group P or Group S (n = 25). Spinal anesthesia was performed with 10 mg of intrathecal bupivacaine. Effective anesthesia was defined as a T-6 or higher sensory block (lost to pinprick) level achieved in 10 minutes after spinal injection, with no patient complaints of pain during surgery. The primary outcome was the percentage of effective anesthesia. Characteristics of spinal anesthesia and side effects were also studied. Results: Percentage of effective anesthesia was lower in Group P than in Group S (68% vs. 92%, P = 0.034). Block level was lower in Group P than in Group S (T-6 vs. T-4, P < 0.001). Onset time to T-5 was slower in Group P than in Group S (7.8 +/- 1.4 vs. 6.3 +/- 1.5, P = 0.003). Incidence of hypotension was significantly lower in Group P than in Group S (8% vs. 40%, P = 0.008). Conclusion: A higher dose of intrathecal bupivacaine is needed when phenylephrine infusion is chosen to prevent spinal-induced hypotension in cesarean sections under spinal anesthesia or CSEA.