A newborn is transferred to the neonatal intensive care unit 4 hours after delivery due to cyanosis. The infant was born via a spontaneous vaginal delivery at 41 weeks gestation to a 22-year-old gravida 2 para 2 woman. The pregnancy and delivery were uncomplicated. Three hours after delivery, circumoral cyanosis was noted after the infant was breastfed. Pulse oximetry readings were 98% in the right hand and 83% in the left foot. On physical examination, the patient has subcostal retractions and grunting. Cardiac examination reveals a 2/6 systolic murmur at the left lower sternal border. Femoral pulses are strong bilaterally. Which of the following is the most likely cause of this infant's cyanosis?

Question

A newborn is transferred to the neonatal intensive care unit 4 hours after delivery due to cyanosis.  The infant was born via a spontaneous vaginal delivery at 41 weeks gestation to a 22-year-old gravida 2 para 2 woman.  The pregnancy and delivery were uncomplicated.  Three hours after delivery, circumoral cyanosis was noted after the infant was breastfed.  Pulse oximetry readings were 98% in the right hand and 83% in the left foot.  On physical examination, the patient has subcostal retractions and grunting.  Cardiac examination reveals a 2/6 systolic murmur at the left lower sternal border.  Femoral pulses are strong bilaterally.  Which of the following is the most likely cause of this infant's cyanosis?

Quizplus · Accepted Answer

11ec160b_3a99_ec82_9249_7fe15b55c31d_MD0001_00 This infant has central cyanosis, a condition characterized by blue discoloration of the mucous membranes and/or skin (not confined to the distal extremities). Central cyanosis is caused by circulation of deoxygenated hemoglobin because of a pulmonary, cardiac, or hematologic condition. In this case, the neonate also has a postductal (left foot) oxygen saturation level that is significantly lower than the preductal saturation (right hand) measurement. This differential cyanosis (or differential hypoxemia) suggests that some deoxygenated blood from the pulmonary artery is flowing to the aorta and mixing with oxygenated blood from the left ventricle. In other words, this patient has an extracardiac right-to-left shunt across a patent ductus arteriosus (PDA), a condition typically associated with persistent pulmonary hypertension of the newborn (PPHN) or congenital heart diseases with left-sided outflow tract obstruction (eg, severe aortic coarctation). PPHN results from failure of pulmonary vascular resistance (PVR) to decline following birth, and is more likely given this patient's strong femoral pulses (as opposed to the diminished pulses seen in left-sided outflow tract obstruction). In PPHN, suprasystemic pulmonary arterial pressure drives deoxygenated blood through the PDA to the aorta. Tricuspid regurgitation, which can occur in PPHN due to elevated PVR leading to tricuspid valve insufficiency, is the likely cause of this neonate's murmur. Patients also typically have respiratory distress (eg, grunting, retractions) within hours of birth due to an underlying pulmonary pathology (eg, pulmonary hypoplasia, meconium aspiration). (Choices A, B, and C) Left-to-right shunts through septal defects and PDAs are characterized by oxygenated blood crossing back into the right-sided circulation. Therefore, cyanosis does not occur. (Choices D and F) Examples of intracardiac right-to-left shunts include a patent foramen ovale in PPHN and a ventricular septal defect in tetralogy of Fallot. Because the mixing of deoxygenated and oxygenated blood occurs within the heart in these cases, preductal and postductal saturations would be equally low. Educational objective: Differential cyanosis (ie, postductal < preductal oxygen saturation) in a neonate suggests right-to-left shunting across a patent ductus arteriosus, such as in persistent pulmonary hypertension of the newborn (PPHN). Patients with PPHN typically have an underlying pulmonary disorder with respiratory distress and strong femoral pulses.

A Newborn Is Transferred to the Neonatal Intensive Care Unit