Norepinephrine versus phenylephrine on cerebral tissue oxygen saturation during prophylactic infusion to prevent spinal hypotension for Caesarean birth

Background: Phenylephrine may cause a reduction in maternal cerebral tissue oxygen saturation (SctO 2 ) during Caesarean birth to prevent spinal hypotension; however, the effect of norepinephrine has not been assessed. We hypothesized that norepinephrine was more effective than phenylephrine in maintaining SctO 2 when preventing spinal hypotension during Caesarean birth. Methods: We conducted a randomized, double-blind, controlled study. Sixty patients were randomly assigned to prophylactic norepinephrine or phenylephrine to maintain blood pressure during spinal anesthesia for Caesarean birth. SctO 2 , systolic blood pressure, and heart rate were recorded. The primary outcome was the incidence of a 10% reduction of intraoperative SctO 2 from baseline or more during Caesarean birth. Results: The norepinephrine group had a lower incidence of more than 10% reduction of intraoperative SctO 2 from baseline than that of the phenylephrine group (13.3% vs 40.0%, P = .02). The change in SctO 2 after 5 minutes of norepinephrine infusion was higher than that after phenylephrine infusion (−3.4 ± 4.7 vs −6.2 ± 5.6, P = .04). The change in SctO 2 after 10 minutes of norepinephrine infusion was higher than that after phenylephrine infusion (−2.5 ± 4.4 vs −5.4 ± 4.6, P = .006). The norepinephrine group showed greater left- and right-SctO 2 values than the phenylephrine group at 5 to 10 minutes. However, the change in systolic blood pressure was comparable between the 2 groups. Conclusion: Norepinephrine was more effective than phenylephrine in maintaining SctO 2 when preventing spinal hypotension during Caesarean birth. However, the changes in clinical outcomes caused by differences in SctO 2 between the 2 medications warrant further studies.