Why does hypotension occur after fetal delivery in a cesarean section (C-section)?

From the Guidelines

Hypotension occurs after fetal delivery in a C-section due to a combination of physiological changes, including decreased uterine size, hormonal shifts, blood volume redistribution, and anesthesia effects. These changes can lead to a temporary drop in systemic blood pressure, and healthcare providers must be prepared to manage this condition to prevent severe effects on the mother and fetus 1. Some key factors contributing to hypotension in this context include:

• Decreased uterine size: As the fetus is removed, the uterus rapidly shrinks, reducing pressure on blood vessels in the abdomen.
• Hormonal shifts: There's a sudden decrease in pregnancy hormones like progesterone and estrogen, which affects vascular tone.
• Blood volume redistribution: Blood that was supplying the placenta is redirected, causing a temporary drop in systemic blood pressure.
• Anesthesia effects: Spinal or epidural anesthesia used in C-sections can cause vasodilation, contributing to blood pressure reduction. To manage hypotension, healthcare providers closely monitor blood pressure and may administer intravenous fluids or vasopressors like phenylephrine if needed, as studies show that a combination of vasopressors and adequate fluid therapy could be effective in reducing the incidence and severity of hypotension 1. Additionally, oxytocin is given to promote uterine contraction, which helps stabilize blood pressure, and patients should be aware that some lightheadedness is normal but severe drops require immediate medical attention 1. Understanding these changes helps healthcare providers anticipate and manage blood pressure fluctuations, ensuring safer C-section procedures.

From the FDA Drug Label

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

Hypotension after fetal delivery in a C-section may be associated with the use of neuraxial anesthesia. The exact cause of hypotension is not explicitly stated in the label, but it is commonly associated with other adverse reactions such as nausea and vomiting. 2

From the Research

Causes of Hypotension after Fetal Delivery in C-Section

• Hypotension after fetal delivery in a C-section can be caused by various factors, including the use of oxytocin and carbetocin, which are commonly used to prevent uterine atony 3.
• The administration of oxytocin and carbetocin can lead to a decrease in systolic arterial pressure, with a mean decrease of 28 mmHg and 26 mmHg, respectively 3.
• The decrease in blood pressure is greatest immediately after administration, with the effect of carbetocin lasting slightly longer than oxytocin 3.
• Other factors that may contribute to hypotension after C-section include the use of spinal anesthesia, which can cause a decrease in blood pressure due to sympathetic blockade 4, 5.
• The application of fundal pressure during C-section can also produce significant hemodynamic effects, including a decrease in cardiac output and blood pressure 6.

Hemodynamic Changes during C-Section

• Hemodynamic changes during C-section can be significant, with changes in cardiac output, heart rate, and blood pressure 4, 5, 3.
• The use of vasopressors such as phenylephrine and ephedrine can help maintain blood pressure during spinal anesthesia for C-section 4, 5.
• However, the choice of vasopressor and the dosage used can affect the incidence of hypotension and other hemodynamic changes 4, 5.
• Close monitoring of blood pressure and other hemodynamic parameters is essential during C-section to quickly identify and treat any changes that may occur 7.