Rosh Pediatrics Practice Exam

What physiological process is absent in a patient with patent ductus arteriosus that normally occurs at birth?

1. Failure of foramen ovale closure

2. Increase in prostaglandin E2

3. Systemic oxygen saturation decreases

4. Systemic oxygen saturation increases

The correct answer is: Systemic oxygen saturation increases

In the context of patent ductus arteriosus (PDA), the process that is typically absent at birth is the increase in systemic oxygen saturation. Normally, when a baby is born and takes its first breaths, there is a significant shift in circulation. The lungs expand, leading to increased oxygenation of blood and a rise in systemic oxygen saturation as blood flows through the now-functioning pulmonary circuit. In the case of a patient with PDA, the ductus arteriosus remains open (patent). This condition allows blood to continue shunting from the aorta to the pulmonary artery, which can lead to excessive blood flow to the lungs. Despite the heart functioning properly, the presence of PDA prevents the normal elevation in systemic oxygen saturation that would occur because some oxygenated blood is mixed with deoxygenated blood, impacting overall oxygen availability to the body's tissues. Therefore, the absence of this normal physiological increase in systemic oxygen saturation at birth marks a significant difference in patients with PDA compared to healthy newborns, who typically experience this increase due to proper circulatory changes.