A physician monitoring a newborn infant’s hea sounds using a stethoscope hears the characteristic murmur of a patent ductus aeriosus. How soon after bih should this murmur normally disappear?
**Core Concept**
Patent ductus arteriosus (PDA) is a congenital heart defect characterized by the failure of the ductus arteriosus, a vascular structure connecting the pulmonary artery to the aorta, to close after birth. Normally, the ductus arteriosus closes within the first 24 hours of life due to the decrease in pulmonary vascular resistance and increase in oxygen tension.
**Why the Correct Answer is Right**
The murmur of a PDA is typically a continuous murmur ("machinery" murmur) best heard at the left upper sternal border. The murmur is caused by the shunting of blood from the aorta to the pulmonary artery through the patent ductus arteriosus. In a normal newborn, the ductus arteriosus closes within the first 24 hours of life due to the increase in oxygen tension and the decrease in prostaglandin E2 levels, which are responsible for keeping the ductus arteriosus patent. However, in some cases, the ductus arteriosus may remain patent, leading to a continuous murmur.
**Why Each Wrong Option is Incorrect**
* **Option A:** While a PDA may be diagnosed in a newborn, a murmur may be present for several weeks before closure, but it should normally disappear by 1-2 weeks of life.
* **Option B:** Closure of the ductus arteriosus is not typically delayed until 2 weeks of age.
* **Option C:** A murmur due to a PDA should not persist beyond 1-2 weeks of life in a normal newborn.
**Clinical Pearl / High-Yield Fact**
A patent ductus arteriosus should be suspected in a newborn with a continuous murmur and respiratory distress, particularly if there is a history of prematurity or maternal diabetes.
**Correct Answer: C.**