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Chapter 51: Approach to the Cyanotic Infant

Satyan Lakshminrusimha; Robin H. Steinhorn

INTRODUCTION

Cyanosis, or bluish discoloration of the skin, is derived from the Greek word kuaneos, meaning “dark blue.” Cyanosis is caused by the presence of deoxygenated hemoglobin in the blood vessels that is most visible on the surface of the skin and mucosa. The mechanisms of cyanosis are outlined in Table 51-1 and Figure 51-1. In general, cyanosis occurs because (1) the binding of oxygen to hemoglobin is abnormal, so that blood does not carry much oxygen despite having a normal partial pressure of oxygen, or PO2 (eg, methemoglobin or carboxyhemoglobin); (2) the perfusion of the skin is poor, such that the venous and capillary blood are very deoxygenated even though the arterial blood may be well oxygenated (eg, cold environment or circulatory shock); or (3) the arterial, and therefore the capillary and venous blood, is poorly oxygenated (eg, a right-to-left shunt with congenital cardiac disease, parenchymal pulmonary disease, or hypoventilation).

Figure 51-1

Mechanisms of cyanosis in newborn infants. Decreased inspired oxygen concentration, airway abnormalities, lung disease (by ventilation-perfusion mismatch), abnormalities of hemoglobin, poor perfusion, polycythemia, heart disease (reduced pulmonary blood flow or right-to-left shunting or poor perfusion), and hypoventilation and fatigue can result in cyanosis. PVR, pulmonary vascular resistance; RV, right ventricle. (Used with permission from Satyan Lakshminrusimha and Robin Steinhorn.)

A diagram depicts the mechanism of cyanosis in newborn babies.
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TABLE 51-1PATHOGENESIS OF CYANOSIS IN THE NEWBORN INFANT
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TABLE 51-1PATHOGENESIS OF CYANOSIS IN THE NEWBORN INFANT
Mechanism for Cyanosis Key Findings Examples
Abnormal hemoglobin, normal arterial PO2 (rare) Normal perfusion, normal respiratory pattern COHb (usually SpO2 normal); MetHb (SpO2 85%),
High hemoglobin concentration, slightly decreased arterial PO2 and arterial SpO2, normal venous and capillary PO2 Cyanotic extremities, normal central pulses, normal respiratory pattern, or tachypnea Polycythemia
Normal or slightly decreased arterial PO2, very decreased venous and capillary PO2 Cyanotic extremities, normal central pulses, normal respiratory pattern Acrocyanosis, cold environment
  Cyanotic or pale extremities, poor pulses, prolonged capillary refill, tachycardia; respiratory distress; consistent with circulatory shock

Aortic atresia, coarctation; myocardial dysfunction

Note: if pulses greater in upper vs lower extremities, consider coarctation or interrupted aortic arch; if SpO2 greater in upper vs lower extremities, consider pulmonary hypertension or coarctation with R-L ductus shunt; if SpO2 greater in lower vs upper extremities, consider transposition with aortic arch obstruction
Decreased arterial PO2 Normal respiratory pattern, decreased pulmonary blood flow, normal perfusion with or without murmurs → intracardiac R-L shunt Tetralogy of Fallot, tricuspid atresia, pulmonary stenosis or atresia
  Normal respiratory pattern, normal or increased pulmonary blood flow, normal perfusion → intracardiac R-L shunt Transposition
  Respiratory distress and pulmonary edema with poor systemic perfusion Left heart inlet or outlet obstruction
  Severe respiratory distress, consolidation, collapse, airway obstruction Pulmonary parenchymal disease or airway obstruction
Decreased arterial PO2...

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