title: The use of phenylephrine to obtund oxytocin-induced hypotension and tachycardia during caesarean section.
abstract: BACKGROUND
  Oxytocin causes clinically significant hypotension and tachycardia. This study examined whether prior administration of phenylephrine obtunds these unwanted haemodynamic effects.
  
  
  METHODS
  Forty pregnant women undergoing elective caesarean section under spinal anaesthesia were randomised to receive either an intravenous 50 μg bolus of phenylephrine (Group P) or saline (Group S) immediately before oxytocin (3U over 15s). Systolic blood pressure, diastolic blood pressure, mean arterial pressure and heart rate were recorded using a continuous non-invasive arterial pressure device. Baseline values were averaged for 20s post-delivery. Between-group comparisons were made of the mean peak changes in blood pressure and heart rate, and the mean percentage changes from baseline, during the 150s after oxytocin administration.
  
  
  RESULTS
  The mean ± SD peak percentage change in systolic blood pressure was -16.9 ± 2% in Group P, and -19.0 ± 1.9% in Group S and the estimated mean difference was 2.1% (95% CI -3.5% to 7.8%; P=0.44); corresponding changes in heart rate were 13.5 ± 2.3% and 14.0±1.5% and the mean estimated difference was 0.5% (95% CI -6.0% to 5%; P=0.87). The mean percentage change from the baseline measurements during the 150s period of measurement was greater for Group S than Group P: systolic blood pressure -5.9% vs -3.4% (P=0.149); diastolic blood pressure -7.2% vs -1.5% (P=0.014); mean arterial pressure -6.8% vs -1.5% (P=0.007); heart rate 2.1% vs -2.4% (P=0.033).
  
  
  CONCLUSIONS
  Intravenous phenylephrine 50 μg immediately before 3U oxytocin during elective caesarean section does not prevent maternal hypotension and tachycardia.
authors.affiliation: Department of Anaesthesia, University of Cape Town, Cape Town, South Africa. Electronic address: crumboll@gmail.com.
authors.forename: C K
authors.initials: CK
authors.lastname: Rumboll
authors.affiliation: Department of Anaesthesia, University of Cape Town, Cape Town, South Africa.
authors.forename: R A
authors.initials: RA
authors.lastname: Dyer
authors.affiliation: Biostatistics Unit, South African Medical Research Council, Cape Town, South Africa.
authors.forename: C J
authors.initials: CJ
authors.lastname: Lombard
mesh_terms: D000328:Adult; D000773:Anesthesia, Obstetrical; D000775:Anesthesia, Spinal; D001794:Blood Pressure / Q000187:drug effects; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002585:Cesarean Section; D004311:Double-Blind Method; D005260:Female; D006801:Humans; D007022:Hypotension / Q000139:chemically induced / Q000517:prevention & control*; D010120:Oxytocics / Q000009:adverse effects; D010121:Oxytocin / Q000009:adverse effects*; D010656:Phenylephrine / Q000494:pharmacology*; D011247:Pregnancy; D011446:Prospective Studies; D013610:Tachycardia / Q000139:chemically induced / Q000517:prevention & control*; D055815:Young Adult
chemical_list: D002316:Cardiotonic Agents; D010120:Oxytocics; D010656:Phenylephrine; D010121:Oxytocin
keywords: Caesarean section; Maternal haemodynamics; Oxytocin; Phenylephrine