Safety of Phenylephrine in Antihypotensive Treatment during Spinal Anesthesia for Cesarean Section

Abstract

Objective: In Thailand, hypotension after spinal anesthesia for cesarean section is routinely treated by ephedrine. As incidence of fetal acidosis reportedly increases resulting from placental transfer, phenylephrine, an α1 agonist with less lipid solubility, becomes an alternative. However, the potential development of serious bradycardia is a concern. The objectives were to investigate the incidence of serious bradycardia, identify associated risk factors and other side effects of phenylephrine. Materials & Methods: This descriptive cross-sectional study was conducted from July 1, 2014 to March 15, 2015 on 509 parturients undergoing cesarean section under spinal anesthesia. Predelivery hypotension was treated by intravenous (IV) phenylephrine 100 mcg and pretherapeutic heart rate (pHR) was recorded. If serious bradycardia (HR < 60 bpm and hypotension or HR < 45 bpm) developed, atropine 0.6 mg was administered IV. Data were analyzed using multivariable logistic regression. Results & Discussion: Incidence of serious bradycardia was 11% (95% CI: 8.0-14.0). A one bpm increment increase in pHR reduced this incidence by 4% (adjusted OR: 0.96; 95% CI: 0.94-0.98, p<0.001; AuROC: 0.76). As compared to a pHR > 80 bpm, a pHR of 61-80 and ≤ 60 bpm increased the risk by 3.55 times and 12.81 times, respectively. Other risk factors were height, baseline DBP, and anesthetic level at 1st minute. Benign and temporary abnormal ECG readings were also found. Conclusion: Phenylephrine is an alternative vasopressor for antihypotensive treatment during spinal anesthesia for cesarean section. It may induce benign bradycardia which spontaneously recover. The incidence of therapeutic required bradycardia was higher in the parturient who had lower heart rate. However, this can be effectively managed by intravenous atropine. No abnormality of APGAR Scores which is associated with phenylephrine was shown.