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 (SctO2) 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 SctO2 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. SctO2, systolic blood pressure, and heart rate were recorded. The primary outcome was the incidence of a 10% reduction of intraoperative SctO2 from baseline or more during Caesarean birth.

RESULTS

The norepinephrine group had a lower incidence of more than 10% reduction of intraoperative SctO2 from baseline than that of the phenylephrine group (13.3% vs 40.0%, P = .02). The change in SctO2 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 SctO2 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-SctO2 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 SctO2 when preventing spinal hypotension during Caesarean birth. However, the changes in clinical outcomes caused by differences in SctO2 between the 2 medications warrant further studies.

Investigation of the Optimum Baseline Blood Pressure for Spinal Anesthesia to Guide Vasopressor Management for Elective Cesarean Delivery: A Case-Control Design

BACKGROUND

Current guidelines recommend prophylactic vasopressor administration during spinal anesthesia for cesarean delivery to maintain intraoperative blood pressure above 90% of the baseline value. We sought to determine the optimum baseline mean arterial pressure (MAP) reading to guide the management of spinal hypotension.

METHODS

We performed a secondary analysis of data collected from normotensive patients presenting for elective cesarean delivery in a tertiary care institution from October 2018 to August 2020. We compared the magnitude of hypotension in patients who reported nausea versus those who did not, using a case-control design. Baseline MAPs at last office visit, morning of surgery, or operating room (pre-spinal) were determined. We calculated the duration and degree of hypotension using the area under the curve (AUC) when the MAP of the respective patient was below 90% of each baseline.

RESULTS

The patients who experienced nausea (n=45) had longer and more profound periods of hypotension than those who did not develop nausea (n=240). A comparison of AUC using MAP baseline at the last office visit or on the morning of surgery showed a statistically significant between-group difference, P=0.02, and P=0.005, respectively, and no significant between-group difference when 90% of the MAP baseline in the operating room was used.

CONCLUSIONS

Patients had the highest preoperative MAP in the operating room and the AUC was similar for those with and without nausea when the pre-spinal MAP baseline was used. Therefore, maintaining higher intraoperative blood pressure using individual pre-spinal MAP as baseline should reduce intraoperative maternal nausea.

The effect of spinal hypotension and anesthesia-to-delivery time interval on neonatal outcomes in planned cesarean delivery

BACKGROUND

Maternal hypotension after spinal anesthesia, and time from anesthesia to delivery, are potentially modifiable risk factors for neonatal acidosis.

OBJECTIVE

This study aimed to examine the relationship between the time from spinal anesthesia to delivery and spinal hypotension in planned cesarean deliveries and their effect on neonatal outcome, primarily neonatal acidosis.

STUDY DESIGN

We performed a retrospective analysis of women with singleton pregnancy undergoing spinal anesthesia for planned cesarean delivery between 37 0/7 and 41 6/7 weeks' gestation using electronic medical records. The occurrence of spinal hypotension and anesthesia-to-incision and incision-to-delivery intervals (minutes) were the primarily studied variables. In addition, spinal hypotension index was developed to account for the duration and magnitude of maternal hypotension. The 90th percentile for the spinal hypotension index defined the sustained spinal hypotension group. The primary outcome was neonatal acidosis (pH of ≤7.1 or base deficit of ≥12.0). The odds ratios were calculated using univariate and multivariate logistic regression models. The multivariate analysis included sporadic spinal hypotension or sustained spinal hypotension, use of vasopressor treatment, and anesthesia-to-incision and incision-to-delivery intervals.

RESULTS

We included 3150 women in the study. Notably, 43.4% experienced at least 1 event of spinal hypotension (sporadic) and 14.8% experienced sustained spinal hypotension. Neonatal acidosis occurred in 3.4% cases of sporadic spinal hypotension (odds ratio, 1.83; 95% confidence interval, 2.27-2.87) and in 5.8% cases of sustained hypotension (odds ratio, 3.00; 95% confidence interval, 1.87-4.80). Both anesthesia-to-incision and incision-to-delivery intervals were significantly associated with neonatal acidosis as follows: at 90th percentile cutoff, the odds ratios for neonatal acidosis were 3.82 (95% confidence interval, 2.03-7.19) and 2.94 (95% confidence interval, 1.70-5.10), respectively. The use of ephedrine (odds ratio, 2.42; 95% confidence interval, 1.35-4.32) but not phenylephrine (odds ratio, 0.76; 95% confidence interval, 0.34-1.72) treatment was also associated with more cases of neonatal acidosis. The woman's age, gestational age, neonatal birthweight, fetal presentation, and the number of previous cesarean deliveries were not associated with neonatal acidosis. In multivariate analysis, anesthesia-to-incision and incision-to-delivery intervals, use of vasopressor treatment, and sustained spinal hypotension were independently associated with neonatal acidosis. After adjustment, the risk for neonatal acidosis did not increase in women who experienced sporadic spinal hypotension only. Neither neonatal acidosis nor the primary research variables were associated with neonatal complications such as transient tachypnea of the newborn, respiratory distress, or admission to the neonatal unit.

CONCLUSION

Neonatal acidosis in planned cesarean delivery was common. However, serious perinatal consequences were rare. The adverse effects of sustained spinal hypotension and prolonged anesthesia-to-incision and incision-to-delivery intervals on neonatal acid-base balance were additive. This supports the adoption of prevention strategies for spinal hypotension, which is widely evidenced based on the obstetrical anesthesia literature, but still not universally used. Whether the reduction in intraoperative time intervals would benefit the neonate should be determined by future prospective studies.