Prior to surgery, which of the following is the best medical therapy for a new born infant with transposition of the pulmonary artery and aorta? (LQ)
|A||Give prostaglandin E2 to keep the ductus arteriosus open|
|B||Give prostaglandin F2 to close the ductus arteriosus|
|C||Give oxygen to keep the ductus arteriosus open.|
|D||Give indomethacin to keep the ductus arteriosus open.|
a. As the endocardial cushions join to divide the ventricles, the streams of blood from the right and left ventricles are divided as they flow out of the truncus.
b. A spiral septum develops to physically separate the two streams of blood.
c. The fusion of the spiral ridges results in division of the truncus into the pulmonary and aortic arteries.
d. Occasionally the spiral is reversed, resulting in the aorta arising from the right ventricle and the pulmonary artery from the left.
e. This is a complete transposition of the great vessels and produces two completely separate blood systems.
f. This situation obviously is incompatible with life unless some type of mixing of blood can occur between these separate systems. In utero, mixing of blood occurs across the atrial septum and in connections with the placental circulation.
g. Cases that survive to corrective surgery must have a persistent atrial septal defect or patent ductus arteriosus to allow mixing of blood.
h. Therefore, clinical consideration should be to keep the ductus arteriosus open.
i. Usually, at birth, breathing decreases pulmonary resistance and this then reverses flow through the ductus arteriosus.
j. This oxygenated blood (flowing from the aorta into the ductus) inhibits prostaglandin production, which in turn closes the ductus arteriosus.
k. To keep the ductus arteriosus open, prostaglandin E should be given.