Divergent effects of ephedrine and phenylephrine on cardiovascular hemodynamics of near-term fetal sheep exposed to hypoxemia and maternal hypotension.
BACKGROUND
We hypothesized that the administration of ephedrine and phenylephrine for maternal hypotension modifies cardiovascular hemodynamics in near-term sheep fetuses.


METHODS
At 115-136 days of gestation, chronically instrumented, anesthetized ewes with either normal placental function or increased placental vascular resistance after placental embolization were randomized to receive boluses of ephedrine (n = 12) or phenylephrine (n = 12) for epidural-induced hypotension after a short period of hypoxemia. Fetal cardiovascular hemodynamics were assessed by Doppler ultrasonography at baseline, during hypotension and after vasopressor treatment.


RESULTS
During hypotension, fetal PO(2) decreased and proximal branch pulmonary arterial and pulmonary venous vascular impedances increased. Additionally, in the embolized fetuses, the time-velocity integral ratio between the antegrade and retrograde blood flow components of the aortic isthmus decreased. These parameters were restored to baseline conditions by ephedrine but not by phenylephrine. With phenylephrine, weight-indexed left ventricular cardiac output and ejection force decreased in the non-embolized fetuses, and the proportion of isovolumetric contraction time of the total cardiac cycle was elevated in the embolized fetuses.


CONCLUSIONS
After exposure to hypoxemia and maternal hypotension, ephedrine restored all fetal cardiovascular hemodynamic parameters to baseline. Phenylephrine did not reverse fetal pulmonary vasoconstriction or the relative decrease in the net forward flow through the aortic isthmus observed in fetuses with increased placental vascular resistance. Moreover, fetal left ventricular function was impaired during phenylephrine administration.
Erkinaro
T
T
Department of Anesthesiology, Oulu University Hospital, Oulu, Finland. tiina.erkinaro@pp.fimnet.fi
Mäkikallio
K
K
Acharya
G
G
Päkkilä
M
M
Kavasmaa
T
T
Huhta
J C
JC
Alahuhta
S
S
Räsänen
J
J
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure / Q000187:drug effects; D002320:Cardiovascular Physiological Phenomena / Q000187:drug effects*; D004809:Ephedrine / Q000494:pharmacology*; D005260:Female; D005318:Fetal Heart / Q000000981:diagnostic imaging / Q000187:drug effects; D005311:Fetal Hypoxia / Q000503:physiopathology*; D005333:Fetus / Q000098:blood supply*; D006339:Heart Rate / Q000187:drug effects; D006351:Heart Valves / Q000000981:diagnostic imaging / Q000187:drug effects; D007022:Hypotension / Q000503:physiopathology*; D019344:Lactic Acid / Q000097:blood; D010656:Phenylephrine / Q000494:pharmacology*; D010920:Placenta / Q000098:blood supply / Q000000981:diagnostic imaging; D011247:Pregnancy; D011652:Pulmonary Circulation / Q000187:drug effects; D012039:Regional Blood Flow / Q000187:drug effects; D012756:Sheep; D014463:Ultrasonography; D014655:Vascular Resistance / Q000187:drug effects
D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D010656:Phenylephrine; D019344:Lactic Acid; D004809:Ephedrine