A 24-year-old primigravid woman at 36 weeks gestation comes to the physician complaining of lightheadedness and nausea at bedtime. Her pregnancy has been uncomplicated and her past medical history is unremarkable. She takes one multivitamin and one iron tablet daily. Her blood pressure is 115/75 mm Hg when sitting, 110/70 mm Hg when standing, and 80/60 mm Hg when supine. Physical examination shows a uterus consistent in size with 36 weeks gestation. Which of the following is the most likely explanation for this patient's hypotension while supine?

Question

A 24-year-old primigravid woman at 36 weeks gestation comes to the physician complaining of lightheadedness and nausea at bedtime.  Her pregnancy has been uncomplicated and her past medical history is unremarkable.  She takes one multivitamin and one iron tablet daily.  Her blood pressure is 115/75 mm Hg when sitting, 110/70 mm Hg when standing, and 80/60 mm Hg when supine.  Physical examination shows a uterus consistent in size with 36 weeks gestation.  Which of the following is the most likely explanation for this patient's hypotension while supine?

Quizplus · Accepted Answer

Supine hypotension syndrome (or aortocaval compression syndrome) is characterized by hypotension, pallor, sweating, nausea, and dizziness that occur when a pregnant woman lies supine (on her back). Symptoms resolve with sitting, standing up, or when assuming a left lateral decubitus position. It occurs predominantly in women > 20 weeks gestation, and is due to the gravid uterus compressing and obstructing the inferior vena cava. This reduces the venous return (preload), which subsequently lowers the cardiac output leading to hypotension. In severe cases, it can result in loss of consciousness and even fetal demise. (Choice A) Peripheral neuropathies that affect postganglionic autonomic nerves can result in orthostatic hypotension. Diabetes mellitus is the most common cause of autonomic neuropathy in developed countries. (Choice C) The blood pressure falls early in gestation, secondary to a reduction in systemic vascular resistance. However, this would not result in isolated supine hypotension. (Choice D) During pregnancy, there is expansion of the plasma volume and an increase in red blood cell mass. In addition, volume depletion is more likely to cause orthostatic hypotension than supine hypotension. (Choice E) Vasovagal syncope occurs due to concomitant withdrawal of sympathetic efferent activity and enhanced parasympathetic (vagal) activity, which results in bradycardia, vasodilation, and orthostatic hypotension. Educational objective: Pregnant women > 20 weeks gestation can experience compression of the inferior cava by the gravid uterus while in the supine position. This reduces venous return and cardiac output, which can result in hypotension and syncope. __________ References: Supine hypotensive syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/8164943)

A 24-Year-Old Primigravid Woman at 36 Weeks Gestation Comes to the Physician