💨 Definition & Types
• Central cyanosis: lips, mucous membranes, conjunctiva → requires ≥5 g/dL desaturated Hgb
• Peripheral cyanosis (acrocyanosis): hands/feet only, benign in newborns, normal pulse ox
• Differential: cardiac, pulmonary, CNS (hypoventilation), hematologic (methemoglobinemia)
❤️ Congenital Heart Disease
• Hyperoxia test: 100% O2 → respiratory cause improves PaO2; cyanotic CHD minimal change
• Newborn pulse ox screening (after 24h) detects critical CHD (~76% sensitivity)
• Tetralogy of Fallot: can present weeks-months after birth with "Tet spells"
• Preductal vs postductal differential helps with ductal-dependent lesions
⚠️ Methemoglobinemia – Key Clues
• Cyanosis NOT improved with 100% O2
• ABG PaO2 normal (oxygen dissolved in plasma is normal)
• Blood is chocolate-brown (does not turn red with O2)
• Pulse ox reads low (~85%) but not proportional to cyanosis
• Causes: oxidizing agents (nitrates in well water, topical anesthetics, drugs), congenital (Hgb M, enzyme deficiency)
🩺 Other Causes
• Pulmonary: pneumonia, bronchiolitis, asthma — usually PaCO2 elevated
• CNS hypoventilation: seizures, neuromuscular disorders, congenital central hypoventilation syndrome
• Breath-holding spells (cyanotic): ages 6-18 months, triggered by injury/frustration, brief LOC, benign
• Apnea with cyanosis: RSV, pertussis, ALTE, child abuse
📌 Decision strategy: Central cyanosis → assess ABCs, pulse ox, hyperoxia test. Methemoglobinemia = cyanosis + normal PaO2 + chocolate blood. Breath-holding spells = typical age/triggers, rapid recovery, treat iron deficiency if present.