Cerebrovascular effects of IV dopamine in fetal sheep

Preterm newborns often receive IV dopamine to support their mean arterial blood pressure (MAP), but there is little data regarding their cerebrovascular responses. Using chronically-catheterized fetal sheep, we tested the hypothesis that IV dopamine causes dose-dependent cerebral vasoconstriction in immature fetuses. We measured cerebral blood flow (CBF-radiolabeled microspheres) and calculated cerebrovascular resistance (CVR) and cerebral O₂ delivery (OD) in seven near-term ( 132 ± 1d) and eight preterm (93 ± 1d) fetal sheep, two days after catheter placement. Measurements were made at baseline and at four fetal dopamine infusion rates: 2.5, 7.5, 25 and 75 μg/kg/min. Results: (mean ± SEM)Rate Percent Change (compared to baseline) μg/kg/min MAP CBF CVR HR OD 93d 25 10 ± 2% No Δ 76 ± 51% 23 ± 3% No Δ 75 25 ± 5 No Δ 80 ± 33 21 ± 4 No Δ 132d 25 29 ± 4 No Δ 41 ± 12 No Δ No Δ 75 55 ± 3 No Δ 87 ± 23 No Δ No Δ Dopamine, at doses high enough to raise MAP at least 10% above baseline, causes cerebral vasoconstriction in both preterm and near term fetal sheep. This response could be detrimental to cerebral perfusion and O₂ delivery, particularly during hypoxia/ischemia.