A CYANOSED NEWBORN

This baby is most likely to have transposition of the great arteries. There are few congenital cyanotic heart conditions that present on the first day of life, because in most cases the ductus arteriosus remains open at this stage, maintaining pulmonary blood flow in conditions such as pulmonary and tricuspid atresia where pulmonary blood flow would be severely restricted or absent. Severe Ebstein’s anomaly and obstructed total anomalous pulmonary venous drainage can produce early cyanosis, but these conditions are associated with significant respiratory distress. Persistent fetal circulation also results in cyanosis, usually with respiratory distress in the context of a newborn who has suffered a significant hypoxic, hypothermic or hypoglycaemic insult, who has pulmonary hypoplasia or sepsis, or sometimes for unknown reasons. Transposition of the great arteries accounts for up to 5 per cent of congenital heart disease and is the commonest cardiological cause of cyanosis in the newborn. The aorta and pulmonary arteries are transposed such that the right ventricle delivers deoxygenated blood, returning from the systemic circulation, into the aorta and back to the systemic circulation. The left ventricle delivers oxygenated blood, arriving from the lungs, into the pulmonary arteries and back to the lungs. These two parallel circulations would result in the vital organs never receiving oxygenated blood, and hence rapid death, if it was not for mixing in the atria via the foramen ovale and between the aorta and pulmonary arteries via the ductus arteriosus. Chest X-ray may show a narrowed upper mediastinum due to the abnormal position of the aorta and pulmonary arteries. Echocardiography by an experienced operator is necessary to confirm the diagnosis. The hyperoxia test provides a means of diagnosing whether cyanosis is due to cardiac or respiratory disease. Normally arterial PaO2 is greater than 9 kPa and rises to more than 20 kPa after exposure to 90–100 per cent oxygen. If the PaO2 fails to rise, this is strongly suggestive of cyanotic heart disease. Persistent fetal circulation can also result in a lack of response. There is already evidence of tissue hypoxia in this case, as there is a metabolic acidosis. Emergency management involves commencing a prostaglandin infusion to maintain patency of the ductus arteriosus, and to correct the metabolic acidosis. An emergency balloon atrial septostomy will probably be needed to improve mixing of oxygenated and deoxygenated blood at the atrial level. Ultimately, an arterial switch operation will need to be performed to provide an anatomical correction.

KEY POINTS

• Measure oxygen saturations if you have any suspicion that a baby may be cyanosed.

• The absence of a murmur does not exclude congenital heart disease.