During a routine prenatal visit, a 30-year-old woman at 34 weeks gestation reports experiencing episodes of lightheadedness, nausea, and a feeling of impending fainting over the past two weeks. She states that these episodes occur exclusively when she is lying flat on her back. The symptoms resolve rapidly when she turns onto her side. Her pregnancy has been uncomplicated. Her blood pressure is 112/68 mm Hg and her heart rate is 85/min while seated in the clinic. Fetal heart monitoring shows a baseline rate of 145/min with moderate variability and no decelerations. Which of the following is the most likely underlying mechanism for this patient's symptoms?
- AProgesterone-mediated decrease in systemic vascular resistance
- BDisproportionate expansion of plasma volume relative to red blood cell mass
- CUpward displacement of the diaphragm by the enlarging uterus
- Decreased venous return due to inferior vena cava compressionCevap
- EIncreased venous capacitance leading to blood pooling in the lower extremities
Cevap
The symptoms are caused by decreased venous return due to inferior vena cava compression.
The correct answer accurately describes the pathophysiology of supine hypotensive syndrome. In the third trimester, the heavy, gravid uterus mechanically compresses the inferior vena cava when the patient lies in the supine position. This compression impedes venous return to the right atrium, leading to a transient decrease in cardiac output and subsequent cerebral hypoperfusion. Patients characteristically present with lightheadedness, nausea, and presyncope when lying flat. Symptoms rapidly resolve when the patient turns to a lateral decubitus position, which displaces the uterus off the inferior vena cava and restores normal venous return.
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Anahtar Kavram
Supine hypotensive syndrome in pregnancy is caused by mechanical compression of the inferior vena cava by the gravid uterus, leading to decreased venous return and transient cerebral hypoperfusion.