AN APPROACH TO THE DIAGNOSIS OF CYANOTIC NEONATE FOR THE PRIMARY CARE PROVIDER

P. SYAMASUNDAR RAO, MD

Introduction

Newborn infants with distress caused by heart defects may not live unless they are treated correctly and quickly.^1–4 Cyanosis is a crucial manifestation of congenital heart defects (CHDs) in the neonate. Pediatric cardiology consultation and/or an echocardiographic study may assist in making a diagnosis. However, such services may not be readily accessible to all newborn babies. An appreciation of the problems related to cyanotic infants by the primary care physician, whether he/she is a pediatrician or a neonatologist, may be useful. At the outset, it should be emphasized that (1) complex physiological and anatomical alterations take place during and immediately after birth^5–7; (2) severe cyanotic CHD can exist without a cardiac murmur; (3) a loud murmur does not automatically suggest that the reason for the distress in the baby is related to a heart defect; (4) when a murmur is detected, it is not necessarily characteristic for a specified CHD; and (5) lack of cardiomegaly on a chest x-ray image does not eliminate severe CHD.

In this chapter, the author will name the causes of cyanosis in the newborn infant; delineate techniques to distinguish cardiac from noncardiac causes of cyanosis; and describe an approach to formulate a cardiac diagnosis prior to echocardiographic and Doppler studies.

Causes of Neonatal Cyanosis

The etiology of cyanosis may chiefly be categorized into respiratory, cardiac and central nervous system (CNS) disorders, persistent pulmonary hypertension (PPHN), and a miscellaneous group of abnormalities and are listed in Table 10.1.

Table 10.1. Causes of cyanosis

The respiratory disorders may be subgrouped as pulmonary parenchymal disorders and diseases causing mechanical interference with lung function, and are shown in Table 10.2.

Table 10.2. Respiratory disorders causing cyanosis

The cyanotic CHD may be subdivided into 3 groups, depending upon pulmonary vascular markings on a chest x-ray (Table 10.3). PPHN (also referred to as persistent fetal circulation [PFC]) is an important cause of cyanosis; this is because of associated right-to-left shunt across the patent foramen ovale (PFO) and/or patent ductus arteriosus (PDA).

Table 10.3. Heart defects causing cyanosis

CNS disorders, which are likely to cause cyanosis, are shown in Table 10.4; the cyanosis as a rule is related on hypoventilation.

Table 10.4. CNS disorders causing cyanosis

A remarkable group of miscellaneous disorders, which may cause cyanosis, are listed in Table 10.5.

Table 10.5. Miscellaneous disorders causing cyanosis

A diagnosis of the cause of the cyanosis (see Tables 10.1–10.5) can frequently be accomplished by the use of usual clinical evaluation and laboratory studies. Respiratory causes may be assumed if there were complications during pregnancy and/or delivery, fever in the mother before birth, onset of cyanosis within the first few hours following birth, prematurity, inappropriate weight for gestational age, asphyxia neonatorum, meconium staining, and/or low Apgar score. Chest x-ray will more often than not aid in recognizing respiratory problems caused by lung parenchymal disease and those that produce mechanical interference with lung function (see Table 10.2). Arterial blood gas examination is helpful in distinguishing cardiac from lung diseases. The PaCO₂ is increased in pulmonary disorders, but not consistently so in CHDs. Nevertheless, there are some babies in whom it is not easy to distinguish between severe pulmonary disease (PD) and cyanotic CHD.

Improvement in arterial PO₂ following 100% oxygen administration in an oxyhood for a period of 15 minutes^1,9 is helpful in the differential diagnosis; significant increase in the PO₂ occurs in infants with PD while no noteworthy increase in PO₂ (< 10 torr) is seen in cyanotic CHD babies. A PaO₂ >150 torr is extremely suggestive of pulmonary problem. A higher PO₂ in the right radial artery blood sample than that in the umbilical artery sample is suggestive of right-to-left shunt via the ductus arteriosus (DA). This may be secondary either to PPHN or to obstruction of aortic arch (eg, interrupted aortic arch [IAA] and severe aortic coarctation).

Although failure to increase PO₂ with 100% O₂ is greatly indicative of cyanotic CHD, some neonates with severe PD do not demonstrate elevation in PO₂. In such babies, continuous positive airway pressure (CPAP) may be useful in the differentiation of pulmonary from heart disease (Figures 10.1). Application of 8 to 10 cm H₂

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