Which medication is most likely to cause fetal tachycardia when used as a vasopressor?

Ephedrine is known for its ability to increase heart rate, not just in the mother but also potentially in the fetus. It acts as a non-selective adrenergic agonist, stimulating both alpha and beta-adrenergic receptors. The stimulation of beta-1 receptors in the fetal heart can lead to increased heart rate, resulting in fetal tachycardia.

This is particularly relevant during situations in which ephedrine is used as a vasopressor, such as during anesthesia for cesarean sections or other surgical procedures. The hemodynamic changes caused by ephedrine can lead to alterations in placental blood flow and potentially affect fetal heart rate directly.

While other vasopressors like phenylephrine and norepinephrine can influence maternal hemodynamics, they are less likely to cause significant fetal tachycardia compared to ephedrine. Dopamine does also have some risk for tachycardia, but its effects are dose-dependent and primarily on maternal rather than fetal heart rate, making ephedrine the more notable culprit in the context of this question.