Enumerate causes of cyanosis in an infant
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causes of cyanosis in infants neonates
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cyanotic congenital heart disease infants differential diagnosis
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Causes of Cyanosis in an Infant
Cyanosis in an infant reflects reduced oxyhaemoglobin in peripheral or central circulation. It is broadly classified as central (low arterial SaO₂) or peripheral (normal SaO₂, reduced peripheral perfusion).
A. Cardiac Causes
The "5 Ts + others" mnemonic covers the classical cyanotic congenital heart diseases (CCHDs):
| Lesion | Key Feature |
|---|---|
| Tetralogy of Fallot (ToF) | Most common CCHD overall; RV outflow obstruction + VSD + overriding aorta + RVH; "boot-shaped" heart on CXR |
| Transposition of the Great Vessels (TGV/TGA) | Most common cause of cyanosis presenting in the newborn period; aorta from RV, PA from LV — circulations in parallel; incompatible with life without mixing (Bailey & Love's, p. 986) |
| Truncus Arteriosus | Single common arterial trunk; mixing of systemic and pulmonary blood |
| Tricuspid Atresia | Absent tricuspid valve; depends on ASD + VSD for survival |
| Total Anomalous Pulmonary Venous Connection (TAPVC) | Pulmonary veins drain into systemic veins; obstructed form presents with severe cyanosis early |
| Pulmonary atresia | No direct RV-to-PA communication; duct-dependent |
| Critical pulmonary stenosis | Severe RV outflow obstruction |
| Ebstein's anomaly | Downward displacement of tricuspid valve; massive right atrial enlargement |
| Hypoplastic left heart syndrome (HLHS) | Systemic circulation duct-dependent; profound cyanosis + shock |
| Single ventricle / double-inlet LV | Complete mixing lesion |
B. Respiratory Causes
| Condition | Notes |
|---|---|
| Respiratory Distress Syndrome (RDS/HMD) | Surfactant deficiency; premature infants |
| Transient Tachypnoea of the Newborn (TTN) | Retained fetal lung fluid; milder, self-limiting |
| Meconium Aspiration Syndrome (MAS) | Airway obstruction + chemical pneumonitis + pulmonary hypertension |
| Congenital Diaphragmatic Hernia (CDH) | Bowel herniation compressing lung; pulmonary hypoplasia |
| Pneumothorax | Spontaneous or iatrogenic; acute deterioration |
| Pneumonia | Bacterial (GBS, Listeria) or viral (HSV, CMV) |
| Pulmonary hypoplasia | Associated with oligohydramnios, CDH |
| Choanal atresia | Obligate nasal breathers; cyanosis relieved by crying |
| Pierre Robin sequence | Micrognathia → glossoptosis → upper airway obstruction |
| Laryngomalacia / tracheomalacia | Stridor; intermittent cyanosis with feeds or agitation |
C. Persistent Pulmonary Hypertension of the Newborn (PPHN)
- Failure of normal postnatal drop in pulmonary vascular resistance
- Right-to-left shunting through fetal channels (foramen ovale, ductus arteriosus)
- Associated with asphyxia, MAS, sepsis, CDH
- Key feature: differential cyanosis (pre-ductal SpO₂ > post-ductal)
D. Haematological Causes
| Condition | Mechanism |
|---|---|
| Methaemoglobinaemia | Congenital (cytochrome b5 reductase deficiency) or acquired (nitrates, dapsone, benzocaine); chocolate-brown blood; SpO₂ unreliable |
| Polycythaemia | Increased deoxyhaemoglobin; often plethoric appearance |
| Severe anaemia | Reduced O₂ carrying capacity; pallor more prominent |
E. Neurological / Central Causes
| Condition | Notes |
|---|---|
| Hypoxic-ischaemic encephalopathy (HIE) | Central apnoea → hypoventilation |
| Seizures | Apnoea/bradycardia; subtle seizures in neonates |
| Intraventricular haemorrhage (IVH) | Apnoeic episodes in preterm infants |
| Neonatal apnoea of prematurity | Immature respiratory control |
| Intracranial hypertension | Herniation → central apnoea |
| Drug depression | Maternal opioids/sedatives → neonatal respiratory depression |
F. Metabolic / Systemic Causes
| Condition | Notes |
|---|---|
| Hypoglycaemia | Apnoea, seizures → secondary cyanosis |
| Sepsis | Poor perfusion + metabolic acidosis; peripheral + central cyanosis |
| Hypothermia | Peripheral vasoconstriction; acrocyanosis |
| Hypocalcaemia | Seizures → apnoea |
G. Peripheral (Acrocyanosis) — Normal Variant
- Bluish discolouration of hands and feet only in the first 24–48 hours of life
- Due to peripheral vasoconstriction; central colour normal; SpO₂ normal
- No intervention needed; resolves spontaneously
Clinical Approach: Is it Cardiac or Respiratory?
| Feature | Cardiac | Respiratory |
|---|---|---|
| Response to 100% O₂ (hyperoxia test) | SpO₂ stays low (PaO₂ <150 mmHg) | SpO₂ improves |
| Respiratory distress | Often absent or mild | Prominent (grunting, recession) |
| CXR | Abnormal heart size/shape | Lung field abnormality |
| Onset | Birth or after duct closes (day 2–4) | Usually immediately at birth |
| Murmur | May be present | Absent |
Key takeaway: TGA is the most common cause of cyanosis presenting as a cardiac emergency in the newborn period, while ToF is the most common CCHD overall. Always perform the hyperoxia test to distinguish cardiac from respiratory aetiology, and consider PPHN and methaemoglobinaemia as important non-structural causes.
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