CHAPTER 103

Cyanosis in the Newborn

Robin Winkler Doroshow, MD, MMS, MEd, FAAP

Cyanosis is a bluish appearance of the skin resulting from the presence of reduced hemoglobin in the tissues. Central cyanosis, which is detected initially in the oral mucosa and nail beds but is generalized when severe, indicates at least 4 to 5 g/dL reduced hemoglobin. Hypoxemia is usually the cause. This condition is frequently present in neonates with pulmonary pathology but is also among the most common presentations of severe congenital heart disease (CHD).

Because cyanotic CHD in newborns may be life-threatening, it must not go undiagnosed. Most diagnostic studies have minimal risk. Even the risk of cardiac catheterization, which is rarely indicated, is relatively low in this setting. Most of the lesions that cause cyanotic CHD can be palliated or corrected, and the prognosis is good.

Epidemiology

Cyanotic CHD occurs in approximately 2 to 3 of every 1,000 live births. Approximately 80% to 90% of these patients, usually those that are most severely affected, are detected prenatally or in the first 30 days after birth. Failure to diagnose major cyanotic CHD before newborn discharge, however, occurs in at least 10% of cases, resulting in unnecessary morbidity and mortality. Newborns with low pulmonary blood flow or lesions causing poor mixing most often present with obvious cyanosis, although initially they otherwise appear well and comfortable. Those with high pulmonary flow are less blue and often present first with congestive heart failure (CHF) or a murmur; however, the condition may be detected earlier using screening pulse oximetry.

Although fetal diagnosis continues to improve, most cyanotic CHD is not diagnosed before birth. The antenatal history, gestational age, birth weight, and delivery room examination are unremarkable. Failure to identify CHD in the setting of routine obstetric ultrasonography does not rule it out; the sensitivity of such scans in the general population is very low. Congenital heart disease is more likely in some situations that can be anticipated prenatally (Box 103.1). In these settings, increased suspicion may result in antenatal detection using specialized echocardiography.

Clinical Presentation

Neonates with cyanotic CHD often present within the first week after birth with cyanosis of the oral mucosa. In more severe cases, generalized cyanosis occurs. The abnormal color may be more apparent with effort (eg, feeding, passing stool) or crying. Respiratory distress, which is heralded by grunting, nasal flaring, and retractions, is minor or absent in many newborns with cyanotic CHD; this is in striking contrast to those with respiratory disease, such as respiratory distress syndrome or aspiration pneumonia. In cases of severe hypoxia, metabolic acidosis results in poor perfusion and compensatory tachypnea with hyperpnea, a key sign of critical heart disease. Additional findings depend on the nature of the causal lesion (Box 103.2). It is important to note that the absence of associated physical findings does not exclude cyanotic CHD.

Because of the dangers of overlooking ductus-dependent CHD and the suboptimal sensitivity of the physical examination to detect it, all US states (and many other nations) now mandate that newborn screening include pulse oximetry determination(s) prior to discharge, usually at 24 hours of age. This test, often called CCHD (for critical CHD) screening, is a highly sensitive, specific, and cost-efficient means of detecting cyanotic CHD before the cyanosis or other findings become apparent. It allows initiation of intervention (discussed later in this chapter) prior to ductal closure, thereby maintaining the baby’s perfusion and oxygenation, and decreasing morbidity and mortality. This approach, which became widespread at the beginning of the 21st century, is likely to become the most common means of diagnosing life-threatening heart disease in the newborn.

For the purposes of this discussion, the term “cyanosis” includes a positive CCHD screen, even if the infant does not appear blue to the naked eye.

Pathophysiology

Cardiac cyanosis is caused by right-to-left shunting so that systemic venous blood bypasses the pulmonary circulation and enters the systemic circulation. Two conditions usually are necessary to produce this type of shunting: a communication (eg, septal defect) for shunting across the blood and a cause (eg, pulmonic stenosis) for shunting away the blood from the lungs. The most notable exception is simple transposition of the great arteries (TGA), in which the fundamental connections are abnormal and all systemic venous blood is directed to the systemic arterial circulation. Lesions associated with cyanosis may be divided into 3 groups: low pulmonary blood flow (LPBF), high pulmonary blood flow (HPBF), and poor mixing.

The LPBF group consists of tetralogy of Fallot, pulmonary atresia with intact ventricular septum, and nearly any combination of defects that includes pulmonary atresia or severe pulmonic stenosis. Pulmonary flow is diminished and may derive entirely from the ductus arteriosus while it remains patent. Aside from obvious cyanosis (and associated oxygen saturation <80%), neonates often appear well.

The HPBF group includes truncus arteriosus, single ventricle, and combinations of defects that involve mixing of oxygenated and unoxygenated blood and little or no obstruction to pulmonary flow. Although a right-to-left shunt is present, the left-to-right shunt is even greater. Pulmonary venous return is therefore voluminous and contributes disproportionately to systemic output. Cyanosis is less apparent; saturation is greater than 80% and may be as high as 95%. Pulmonary flow increases over the first days and weeks after birth as the pulmonary vascular resistance falls and CHF develops, as in patients with isolated shunt lesions (eg, ventricular septal defect). Some neonates with HPBF lesions also have obstruction to systemic blood flow (eg, coarctation of the aorta, hypoplastic left heart syndrome) and may depend on the ductus arteriosus to carry some or all of this flow.

The poor mixing group is limited to TGA and its variants. The right and left circuits are in parallel rather than in series, and survival depends on interchange of oxygenated and unoxygenated blood between them. Most newborns with poor mixing present with marked cyanosis (ie, saturation <80%), as with patients in the LPBF group.

Severe hypoxemia (ie, partial pressure of oxygen [PO₂] <35 mm Hg for the average newborn) is not compatible with prolonged survival. Neonates experience tissue hypoxia, anaerobic glycolysis, and metabolic acidosis. Respiratory compensation may occur initially. Even with a normal pH, however, the presence of metabolic acidosis (ie, large base deficit) indicates life-threatening hypoxia, necessitating immediate intervention, without which death ensues in a matter of hours.

Differential Diagnosis

The major causes of cyanosis are cardiac (Box 103.3) and respiratory (Box 103.4). Diagnoses in the latter group include problems of the lung, chest, airway, or respiratory drive.

Persistent fetal circulation, or persistent pulmonary hypertension of the newborn, is perhaps the condition that is most often confused with cyanotic CHD. In this condition the heart and great vessels are structurally normal; however, high pulmonary vascular resistance, which is common in postterm newborns with perinatal distress or pulmonary disease, causes blood to shunt away from the lungs at the foramen ovale and ductus arteriosus. Profound cyanosis that is unresponsive to supplemental oxygen, particularly in postductal sites (eg, lower extremities), may be the only abnormal finding, and echocardiography is required to exclude CHD.

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