A ‘blue baby’ is an informal term for a newborn or infant who has a blue or purple tinge to the skin, lips or fingernails, known as cyanosis. Central cyanosis occurs when the level of deoxygenated haemoglobin in the arterial blood is elevated, giving the blood a darker colour that shows through the skin. In a newborn, this most commonly indicates a congenital heart defect that allows deoxygenated blood to bypass the lungs and enter the arterial circulation without being oxygenated, so-called cyanotic congenital heart disease.
Cyanotic congenital heart conditions include Tetralogy of Fallot, transposition of the great arteries, pulmonary atresia, tricuspid atresia, truncus arteriosus, and hypoplastic left heart syndrome. In these conditions, a right-to-left shunt allows deoxygenated blood from the right side of the heart to enter the left side (and therefore the body) without first passing through the lungs. Cyanosis is more pronounced with physical effort as oxygen demand increases. Diagnosis is confirmed by echocardiography, and surgical or catheter-based intervention is typically required in the neonatal period or infancy.
In adults with uncorrected or partially corrected cyanotic congenital heart disease, chronic cyanosis causes compensatory changes including an increase in red blood cell production (polycythaemia) to carry more oxygen, and can lead to Eisenmenger syndrome, in which pulmonary hypertension has become so severe that the shunt reverses. Adults with longstanding cyanosis are managed in adult congenital heart disease (ACHD) specialist centres and require careful monitoring of haematocrit, renal function and oxygen saturation.
Cyanosis can also occur in adults without congenital heart disease, for example in severe lung disease, pulmonary embolism, or low cardiac output states after cardiac arrest. Post-cardiac arrest patients with ongoing hypoxia may appear cyanosed until oxygenation is restored by ventilation and resuscitation. The presence of cyanosis in any context is a signal to assess oxygen levels and cardiac and respiratory function urgently.
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