Vasopressors

Symptoms of maternal hypotension include light-headedness, nausea, difficulty breathing, and diaphoresis. Maternal hypotension may lead to decreased placental perfusion and fetal distress. Sympathetic blockade from regional anesthesia and decreased systemic vascular resistance may cause symptomatic maternal hypotension. An ideal vasopressor for obstetric anesthesia is one that increases both maternal blood pressure and placental blood flow.

1. Ephedrine is an indirect agonist of α- and β-adrenergic receptors. Its inotropic and chronotropic effects increase peripheral and uterine blood flow. Historically, ephedrine was the drug of choice for treatment of maternal hypotension.
2. Phenylephrine was previously believed to increase maternal blood pressure and decreased uteroplacental blood flow, but more recent evidence shows that phenylephrine is at least as effective in correcting maternal hypotension as ephedrine but with less risk of fetal acidemia. Phenylephrine infusions have become increasingly common to prevent and treat maternal hypotension.
3. Dilute norepinephrine may be used to counteract spinal anesthesia-induced hypotension and increases cardiac output with a lower incidence of bradycardia compared with phenylephrine. Less commonly used than ephedrine and phenylephrine, norepinephrine use in labor and delivery is an area of active investigation.