What are the causes and management of hypotension in pregnancy?

From the Guidelines

Hypotension in pregnancy should be managed by positioning the patient on her left side to relieve pressure on the inferior vena cava, improving venous return and cardiac output, as recommended by the 2020 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1. This approach is crucial in ensuring maternal and fetal wellbeing, as hypotension can lead to decreased placental perfusion and fetal distress.

Key Considerations

• The patient's airway, ventilation, and oxygenation should be carefully managed, as pregnant patients are more susceptible to hypoxia due to increased maternal metabolism and decreased functional reserve capacity 1.
• Non-pharmacological interventions, such as adequate hydration and avoiding prolonged standing, should be implemented to prevent hypotension.
• If medication is necessary, ephedrine (5-10 mg IV) or phenylephrine (50-100 mcg IV) may be used, particularly during spinal anesthesia for cesarean delivery.

Treatment of Hypotension

• Treatment of hypotension should be based on presumed underlying causes, including vasodilation, hypovolaemia, bradycardia, and low cardiac output, as recommended by the Perioperative Quality Initiative (POQI) international consensus statement on perioperative arterial pressure management 1.
• Vasodilation can be reversed by vasopressors such as phenylephrine or norepinephrine, while hypovolaemia can be treated with intravascular fluid administration.

Monitoring and Follow-up

• Regular prenatal visits are essential to monitor blood pressure trends, as persistent hypotension may indicate underlying conditions like adrenal insufficiency or severe anemia that require specific treatment.
• The patient's condition should be closely monitored, and any changes in blood pressure or symptoms should be promptly addressed to prevent complications.

From the FDA Drug Label

8 USE IN SPECIFIC POPULATIONS

8.1 Pregnancy Pregnancy Category C Animal reproduction studies have not been conducted with intravenous phenylephrine. It is also not known whether phenylephrine can cause fetal harm when administered to a pregnant woman or can affect reproduction capacity. Phenylephrine hydrochloride should be given to a pregnant woman only if clearly needed.

1. 2 Labor and Delivery The most common maternal adverse reactions reported in studies of phenylephrine use during neuraxial anesthesia during cesarean delivery include nausea and vomiting, which are commonly associated with hypotension, bradycardia, reactive hypertension, and transient arrhythmias Phenylephrine does not appear to cause a decrease in placental perfusion sufficient to alter either the neonate Apgar scores or blood-gas status.

The use of phenylephrine in pregnancy is categorized as Pregnancy Category C, meaning it should be given to a pregnant woman only if clearly needed.

• Hypotension is mentioned as a common adverse reaction associated with phenylephrine use during neuraxial anesthesia in cesarean delivery.
• However, phenylephrine does not appear to cause a decrease in placental perfusion. The decision to use phenylephrine in pregnancy should be made with caution, considering the potential risks and benefits 2.

From the Research

Hypotension in Pregnancy: Key Findings

• Hypotension is a common condition in pregnant women, and its association with pregnancy complications and birth outcomes has been investigated in several studies 3.
• Maternal hypotension is protective against preeclampsia, but hypotensive pregnant women are at higher risk for severe nausea or vomiting, threatened abortion, and anemia 3.
• The position of the patient during blood pressure measurement can affect the reading, with notable reductions in blood pressure measurements observed in the left lateral recumbent position compared to the supported seated position 4.
• The supine position can cause inferior vena cava (IVC) compression and supine hypotensive events, although the spinal venous plexus may provide an alternative pathway for venous return in the presence of IVC compression 5.
• The left lateral tilt (LLT) position is commonly used during MRI in pregnancy to prevent IVC compression and supine hypotensive events, but it may be suboptimal for image quality 5.

Effects of Positioning on Blood Pressure

• Clinically significant differences in blood pressure measurements can occur based on patient positioning, which could affect the clinical management of patients 4.
• The left lateral recumbent position is associated with lower blood pressure measurements compared to the supported seated position 4.
• The supine position can decrease IVC flow, but the spinal venous plexus can act as a complementary venous return system, maintaining vascular homeostasis 5.

Pregnancy Complications and Birth Outcomes

• Maternal hypotension is not associated with a higher risk of congenital abnormalities (CAs) in the offspring, but it is associated with a higher risk of some pregnancy complications, such as severe nausea or vomiting and anemia 3.
• There is no clinically important difference in the rate of preterm births and low birthweight newborns in pregnant women with or without hypotension 3.