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. Pure α₁-adrenergic agents such as phenylephrine were previously believed to increase maternal blood pressure but decrease uteroplacental blood flow. Recent evidence indicates that judicious and precise dosing of phenylephrine is not associated with an increased incidence of fetal acidemia or decreased Apgar scores. Phenylephrine infusions have become increasingly common to prevent and treat maternal hypotension.
3. The more potent vasoconstrictors and inotropes such as norepinephrine and epinephrine are indicated for severe maternal hypotension resistant to volume resuscitation and traditional vasopressors.