title: Phenylephrine infusion versus bolus regimens during cesarean delivery under spinal anesthesia: a double-blind randomized clinical trial to assess hemodynamic changes.
abstract: BACKGROUND
  Phenylephrine is used to prevent and treat hypotension during spinal anesthesia for cesarean delivery. The optimal administration regimen is undetermined. We used a Non-invasive cardiac output monitor to test the hypothesis that a fixed-rate phenylephrine infusion regimen would cause a smaller reduction in maternal cardiac output, and result in less maternal hypotension, as compared to a phenylephrine bolus regimen.
  
  
  METHODS
  This was a double-blind, randomized clinical trial of women undergoing elective cesarean delivery under spinal anesthesia. Patients were randomized to an intermittent bolus (120 μg) or a fixed-rate infusion (120 μg/min) regimen of phenylephrine. Any decrease in systolic blood pressure from baseline was treated. The primary outcome was the maximum change in cardiac output in the predelivery period, assessed using bioreactance technology. Secondary outcomes included the maximum change in heart rate, incidence of hypo- and hypertension, nausea/vomiting and bradycardia, total dose of phenylephrine, umbilical blood gases, and Apgar scores. The hemodynamic profiles over time in each treatment arm were compared.
  
  
  RESULTS
  Sixty patients were studied. There was no significant difference in the maximum change in cardiac output between the 2 treatment arms: mean (SD) maximum change in cardiac output in the bolus group was 1.87 (1.68) L/min versus 1.9 (1.46) L/min in the infusion group (P = 0.94) (95% confidence intervals of difference in means: -0.84 to 0.78 L/min). The infusion group received significantly more phenylephrine (1740 (613) versus 964 (454) μg) (P < 0.001). In the initial 6 min after intrathecal injection, there was a significant decrease in blood pressure in the infusion group compared to the bolus group (P = 0.007). There was no significant difference in the other secondary outcomes.
  
  
  CONCLUSIONS
  There were no clinical benefits to administering phenylephrine as an infusion versus a bolus regimen. The bolus regimen maintained maternal arterial blood pressure closer to baseline in the initial minutes after spinal injection but this had no clinical benefits. The infusion regimen required a higher total dose of phenylephrine to maintain maternal arterial blood pressure at baseline during the predelivery period.
authors.affiliation: Department of Anesthesia and Pain Management, Mount Sinai Hospital, University of Toronto, 600 University Avenue, Room 781, Toronto, ON M5G 1X5, Canada. anneedoherty@yahoo.com
authors.forename: Anne
authors.initials: A
authors.lastname: Doherty
authors.forename: Yayoi
authors.initials: Y
authors.lastname: Ohashi
authors.forename: Kristi
authors.initials: K
authors.lastname: Downey
authors.forename: Jose C A
authors.initials: JC
authors.lastname: Carvalho
mesh_terms: D000328:Adult; D000773:Anesthesia, Obstetrical / Q000379:methods*; D000775:Anesthesia, Spinal / Q000379:methods*; D001794:Blood Pressure / Q000187:drug effects; D002302:Cardiac Output / Q000187:drug effects; D002585:Cesarean Section / Q000379:methods*; D003627:Data Interpretation, Statistical; D004311:Double-Blind Method; D005260:Female; D006339:Heart Rate / Q000187:drug effects; D006439:Hemodynamics / Q000187:drug effects*; D006801:Humans; D007262:Infusions, Intravenous; D007275:Injections, Intravenous; D009407:Nerve Block; D010656:Phenylephrine / Q000008:administration & dosage* / Q000494:pharmacology*; D011247:Pregnancy; D013318:Stroke Volume / Q000187:drug effects; D016896:Treatment Outcome; D014655:Vascular Resistance / Q000187:drug effects; D014662:Vasoconstrictor Agents / Q000008:administration & dosage* / Q000494:pharmacology*
chemical_list: D014662:Vasoconstrictor Agents; D010656:Phenylephrine