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INTRODUCTION

The physical signs of cyanosis and decreased oxygen saturation are usually the result of hypoxemia, and can be found in newborn infants with a variety of pathologies. Hypoxemia can be the result of shunting of deoxygenated blood from the venous to the arterial circulation. This can occur at many levels including intracardiac, extracardiac, and intrapulmonary locations. The primary causes of hypoxemia in infants without congenital heart disease vary and include pulmonary problems such as pneumonia, respiratory distress syndrome (RDS), congenital anomalies, pneumothorax, and meconium aspiration syndrome (MAS). Additionally, the primary cause of hypoxemia could be persistent pulmonary hypertension of the newborn (PPHN), a failure or delay in making the circulatory transition from fetal to newborn life leading to persistently elevated pulmonary vascular resistance, and continued shunting through the fetal channels. In most cases, PPHN is secondary to another respiratory disease, and therefore these findings do not usually occur in isolation. Certain conditions predispose infants to having a more prolonged circulatory transition. Infants at higher risk include infants of diabetic mothers, infants with trisomy 21, and fetal exposure to nonsteroidal anti-inflammatory agents or selective serotonin reuptake inhibitors. Preterm infants may have a variety of transitional problems after birth leading to hypoxemia. Both RDS and prolonged premature rupture of membranes (PPROM) are associated with PPHN. Additionally, a significant patent ductus arteriosus (PDA) is often associated with increasing oxygen and ventilator requirements. Echocardiography can be helpful in the diagnosis and management of many of these problems.

To differentiate the causes of hypoxemia, the neonatologist should perform and interpret a complete, comprehensive echocardiographic study to exclude congenital heart disease. When interpreting the echocardiogram, one must consider the clinical circumstances associated with the presentation. The neonatologist is in a unique position to be thoroughly involved with the clinical care of the infant and can determine whether the clinical course and the echocardiography findings are congruent. When the clinical course and the echocardiography findings are inconsistent, it is important for the neonatogolist to further evaluate all of the findings. The neonatologist performing echocardiography should readily refer to a pediatric cardiologist whenever congenital heart disease is suspected. In recent years, routine oxygen saturation screening of the newborn prior to discharge from the hospital has been recommended to detect otherwise silent critical congenital heart disease that could cause serious complications if left undetected.1,2 These screens have frequently identified infants with hypoxemia not caused by critical congenital heart disease. Approximately one-third of the infants with a positive screen result that is not associated with critical congenital heart disease will have another illness requiring treatment.3,4

In addition to assessment of the immediate transitional problems that cause hypoxemia, echocardiography can be helpful in evaluating infants at any time during the neonatal intensive care unit course when clinical deterioration occurs. Infants on the ventilator may have impaired cardiac function because of excessive intrathoracic pressure. Pleural and pericardial effusions can develop as complications ...

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