Aortocaval compression syndrome

Overview

Aortocaval Compression Syndrome—also known as supine hypotensive syndrome, is a condition that occurs when the gravid uterus (enlarged during pregnancy) compresses the abdominal aorta and inferior vena cava when a pregnant individual lies flat on their back. This compression restricts blood flow to the heart and can reduce cardiac output, leading to a drop in blood pressure and symptoms of hypotension and decreased perfusion.

It most commonly affects pregnant women during the second or third trimester, but it may also occur during surgical procedures or trauma in pregnancy when the patient is in a supine position.

Causes

Aortocaval Compression Syndrome is primarily caused by the anatomical changes of late pregnancy:

• Enlarged uterus: Compresses the inferior vena cava (which returns blood from the lower body to the heart) and, to a lesser extent, the abdominal aorta

• Supine position: Lying flat allows the uterus to rest directly on the aortocaval structures

Additional contributing factors may include:

• Multiple gestation pregnancies

• Polyhydramnios (excess amniotic fluid)

• Large fetal size or uterine masses

Symptoms

Symptoms of aortocaval compression syndrome typically occur within minutes of assuming a supine position and may include:

• Dizziness or lightheadedness

• Hypotension (low blood pressure)

• Pallor and sweating

• Nausea or a feeling of faintness

• Tachycardia (rapid heart rate)

• Shortness of breath or chest discomfort

• Fetal distress: If uteroplacental blood flow is compromised

Symptoms resolve quickly upon repositioning, usually by turning the patient onto the left side, which relieves pressure on the vessels.

Diagnosis

Aortocaval compression syndrome is usually diagnosed clinically based on symptoms and response to positional changes. Diagnostic steps may include:

• Physical examination: Assessing for hypotension, tachycardia, and symptom onset in the supine position

• Fetal monitoring: May reveal late decelerations or decreased fetal heart rate variability during maternal hypotension

• Doppler ultrasound: May demonstrate reduced blood flow in the inferior vena cava when supine

Formal imaging is rarely necessary unless symptoms persist in multiple positions or other causes are suspected.

Treatment

Treatment is primarily supportive and involves positional adjustments to relieve vessel compression:

Immediate Management:

• Left lateral tilt position: Turning the patient onto her left side or placing a wedge under the right hip at a 15–30° angle

• Monitoring vitals and fetal status: Continuous assessment during labor or surgical procedures

Preventive Measures:

• Instruct pregnant patients (especially in the third trimester) to avoid lying flat on their back

• Use of lateral positioning during surgeries, imaging, or labor

Advanced Care (rarely required):

• IV fluids and oxygen support if symptoms persist

• Emergency delivery if there is sustained fetal distress and maternal compromise

Prognosis

The prognosis for aortocaval compression syndrome is excellent when promptly recognized and corrected. Most symptoms resolve immediately with position changes, and long-term effects are rare.

Unrecognized or prolonged compression can lead to maternal hypotension, reduced uteroplacental perfusion, and fetal hypoxia. Therefore, awareness and preventive care in late pregnancy and during procedures are essential to avoid complications.