Cyanotic Heart Defects

A newborn turns blue during feeding and squats instinctively as a toddler — these aren't random behaviors. They're survival mechanisms for a heart that shunts blood away from the lungs.

Cyanotic heart defects involve right-to-left shunting, meaning deoxygenated blood bypasses the lungs and enters systemic circulation, producing central cyanosis. The classic mnemonic is the 5 T's: Tetralogy of Fallot (TOF), Transposition of the Great Arteries (TGA), Truncus Arteriosus, Tricuspid Atresia, and Total Anomalous Pulmonary Venous Return (TAPVR). TOF is the most common cyanotic defect and has four components: ventricular septal defect, overriding aorta, right ventricular outflow obstruction (pulmonary stenosis), and right ventricular hypertrophy. Hypercyanotic 'tet spells' occur when pulmonary outflow obstruction worsens suddenly — the infant becomes deeply cyanotic, agitated, and hyperpneic. Immediate nursing response: place the child knee-to-chest position (squatting posture) to increase systemic vascular resistance, which forces more blood through the pulmonary circuit. Oxygen is applied, morphine may be given to reduce respiratory drive. TGA presents within hours of birth with severe cyanosis unresponsive to supplemental oxygen — survival depends on maintaining a PDA with prostaglandin E1 infusion until surgical repair. Newborn pulse oximetry screening flags saturations below 95% (or a >3% difference between right hand and foot) for further evaluation of critical congenital heart disease.

Key Distinctions

Don't confuse cyanotic (right-to-left shunt, blue baby) with acyanotic defects (left-to-right shunt, pink but overloaded lungs leading to heart failure). Students mix up tet spells with seizures — tet spells have cyanosis and respond to knee-to-chest, not anticonvulsants. TGA cyanosis does NOT improve with oxygen; if oxygen fails to raise sats, think structural shunt, not respiratory problem.

Clinical Pearl

Blue baby + oxygen doesn't help = think structural. Knee-to-chest is your tet spell rescue — it's the squat the toddler already knows to do.