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The effect of phenylephrine administration on maternal cerebral tissue oxygenation following spinal anesthesia for cesarean delivery
Abstract Number: OP2-3
Abstract Type: Original Research
Introduction: Phenylephrine (PE) is widely used to treat or prevent hypotension associated with spinal anesthesia in obstetric patients. Its effect on cerebral tissue oxygenation (SctO2) in obstetric patients having spinal anesthesia (SA) has not been described. This might be important in high risk obstetric patients with altered cerebrovascular reactivity such as those with chronic hypertension and preeclampsia. In this observational study we investigated the effects of phenylephrine administered by a bolus vs a prophylactic infusion for the management of hypotension on SctO2 in women having spinal anesthesia for cesarean delivery (CD).
Methods: Following IRB approval ASA 1 and 2 patients scheduled for CD under SA were alternately assigned to either a PE bolus (PEB) or infusion (PEI) group. Measurements of NIBP, CO (Physioflow®) and SctO2 (Foresight®) were obtained at baseline and following the initiation of SA with bupivacaine 12 mg, fentanyl 15 mcg and morphine 150 mcg. 2L of Lactated ringers coload was administered before delivery. Systolic blood pressure (SBP) was maintained within 20% of baseline by titrating a PE infusion initiated at 50 mcg/min according to an algorithm in the PEI group and by administration of 100 mcg PE boluses for the treatment of 20% drop in SBP in the PEB group. The study continued until 10 min after oxytocin administration. We modeled the effect of time, PE administration method and its interaction with time, CO and baseline SctO2 on SctO2 using repeated measures ANCOVA from initiation of spinal anesthesia to 15 min post spinal.
Results: 14 patients were included in the study (7 per group). The median (IQR) dose of PE was 100 (0-1100)mcg in the bolus group vs. 2247 (1323-3163) mcg in the infusion group. There were no differences in SctO2 and CO at initiation of spinal anesthesia. Accounting for PE administration method, baseline SctO2 and time, there was a significant correlation between Sct02 and CO with SctO2 increasing by 0.319% for every 1L/min increase in CO (p=0.0019). SctO2 decreased over time in both groups (p<0.0001) with an additional 0.414% reduction in the PEI vs. PEB group per minute (p=0.0390) (figure 1).
Conclusion: Our results demonstrate that PEI is associated with greater reductions in SctO2 when compared with PEB perhaps as a result of the larger doses and longer administration time by this method. These findings may have implications for patients at increased risk of peripartum cerebrovascular events.