Patent Ductus Arteriosus

Published on 21/03/2015 by admin

Filed under Pediatrics

Last modified 21/03/2015

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Chapter 61 Patent Ductus Arteriosus

PATHOPHYSIOLOGY

The ductus arteriosus is a large vessel that connects the main pulmonary trunk (or left pulmonary artery) with the descending aorta approximately 5 to 10 mm from the origin of the left subclavian artery. Patent ductus arteriosus (PDA) is the persistent patency of the ductus arteriosus after birth, which results in the shunting of blood directly from the aorta (higher pressure) into the pulmonary artery (lower pressure). This left-to-right shunting causes the recirculation of increased amounts of oxygenated blood in the lungs, which raises demands on the left side of the heart. The additional effort required of the left ventricle to meet this increased demand leads to progressive dilation and left atrial hypertension. The cumulative cardiac effects cause increased pressure in the pulmonary veins and capillaries, which results in pulmonary edema. The pulmonary edema leads to decreased diffusion of oxygen and hypoxia, with progressive constriction of the arterioles in the lungs. Pulmonary hypertension and failure of the right side of the heart ensue if the condition is not corrected through medical or surgical treatment. Most PDAs are a left-to-right shunting of blood, but right-to-left ductal shunting may occur with associated pulmonary disease, left-heart obstructive lesions, and coarctation of the aorta. Closure of the PDA depends primarily on the constrictor response of the ductus to the oxygen tension in the blood. Other factors affecting ductus closure include the action of prostaglandins, pulmonary and systemic vascular resistances, the size of the ductus, and the condition of the infant (premature or full-term). PDA occurs more frequently in premature infants; it is also less well tolerated in these infants, because their cardiac compensatory mechanisms are not as well developed and left-to-right shunts tend to be larger.