BJA Advance Access originally published online on December 23, 2005
British Journal of Anaesthesia 2006 96(2):231-237; doi:10.1093/bja/aei305
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Ephedrine and phenylephrine for the treatment of maternal hypotension in a chronic sheep model of increased placental vascular resistance
1 Department of Anaesthesiology and 2 Department of Obstetrics and Gynaecology, Oulu University Hospital, PO Box 21, FIN-90029 OYS, Finland. 3 Department of Obstetrics and Gynaecology, University Hospital of Northern Norway, N-9038 Tromsø, Norway
* Corresponding author. E-mail: tiina.erkinaro{at}pp.fimnet.fi.
Background. We hypothesized that ephedrine and phenylephrine are equal with respect to uterine and placental haemodynamics and fetal acid–base status after exposure to maternal hypoxaemia and hypotension in a chronic sheep model of increased placental vascular resistance (RUA).
Methods. At 114–135 days gestation, chronically instrumented fetal sheep underwent placental embolization leading to increased RUA. Twenty-four hours after embolization, the ewes were anaesthetized and randomized to receive boluses of ephedrine (n=7) or phenylephrine (n=6) for epidural-induced hypotension after maternal hypoxaemia. Uterine (QUtA) and placental (QUA) volume blood flows and uterine vascular resistance (RUtA) and RUA were recorded. Uterine (PIUtA) and umbilical artery (PIUA) pulsatility indices were obtained by Doppler ultrasonography. Fetal arterial blood samples were analysed for acid–base values and lactate concentrations.
Results. During hypotension, QUtA, fetal pH, BE, and 
decreased whereas RUtA, PIUtA, RUA, and fetal lactate concentration increased. With ephedrine, QUtA, RUtA, PIUtA, RUA, and fetal returned to baseline. Fetal pH, BE, and lactate concentration did not change from hypotensive values. With phenylephrine, QUtA remained lower (P=0.007) and RUtA (P=0.007), PIUtA (P=0.013), and RUA (P=0.050) higher than at baseline. Fetal returned to baseline and fetal pH and BE did not change from hypotensive values. However, fetal lactate concentration increased further (mean difference 1.49, 95% confidence interval 0.72–2.26 mmol litre–1; P=0.004).
Conclusions. In a chronic sheep model of increased placental vascular resistance, compared with ephedrine administration, phenylephrine administration was associated with impaired uterine and placental haemodynamics and increased fetal lactate concentrations.
Presented in part at the Euroanaesthesia 2005 Meeting, Vienna, Austria, May 28–31, 2005.
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 Ephedrine and phenylephrine for treatment of maternal hypotension. Br. J. Anaesth., June 1, 2006; 96(6): 804 - 805. [Full Text] [PDF]
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