A 1-hour-old newborn girl is evaluated in the delivery room. The infant was born at term via spontaneous vaginal delivery following an uncomplicated pregnancy. The mother is gravida 2, para 2 with no significant medical history. Apgar scores were 9 and 9 at 1 and 5 minutes. The patient has been skin-to-skin with her mother and breastfed once without difficulty. Physical examination shows a pink, alert infant. Cardiac auscultation reveals a normal S1 and S2 with no murmurs, and femoral pulses are normal. Which of the following hemodynamic changes are most likely to be seen in this newborn as compared to before birth?

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11ec160b_3736_9d30_9249_31384f642a94_MD0001_00 During fetal life, pulmonary vascular resistance (PVR) is high due to hypoxic vasoconstriction in the nonventilated lung. In contrast, systemic vascular resistance (SVR) is relatively low due to the low resistance of the placenta. Therefore, blood bypasses the lungs by flowing through the foramen ovale (from the right to left atrium) and through the ductus arteriosus (from the pulmonary artery to descending aorta). The presence of the ductus arteriosus allows the majority of the right ventricular output to be shunted into the systemic circulation; therefore, the right ventricle provides approximately two-thirds of the fetus' cardiac output. Immediately after birth, when infants take their first breaths, the increased oxygen tension in the lungs cause pulmonary vasodilation and a rapid decrease in PVR. At the same time, umbilical cord clamping removes the low-resistance placenta from the systemic circulation, causing SVR to increase. These pressure changes quickly lead to reversal of blood flow across the ductus arteriosus (ie, left-to-right), eliminating the right ventricular contribution to cardiac output. As a result, the left ventricle becomes responsible for the entire cardiac output. Educational objective: Immediately after birth, decreased pulmonary vascular resistance (due to oxygenation and ventilation of the lungs) and increased systemic vascular resistance (due to removal of the placenta from circulation) reverse the flow across the ductus arteriosus to left-to-right. Because the right ventricle no longer contributes to systemic blood flow, the left ventricle becomes responsible for the total cardiac output.

A 1-Hour-Old Newborn Girl Is Evaluated in the Delivery Room