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CENTRAL CAUSES
- decreased arterial oxygen saturation
-> decreased FiO2 (altitude)
-> lung disease (COPD)
-> V/Q mismatch (PE)
-> right to left shunt (cyanotic congenital heart disease) - polycythaemia
- haemoglobin abnormalities (methaemoglobinaemia, sulphaemoglobinaemia)
PERIPHERAL CAUSES
- all causes of central cyanosis cause peripheral cyanosis
- exposure to cold
- reduced cardiac output (cardiogenic shock, LVF)
- arterial or venous obstruction
CAUSES OF CYANOTIC CONGENITAL HEART DISEASE
5 Ts
- Tetralogy of Fallot (TOF)
- Transposition of the Great Arteries (TGA) — PA and aorta are reversed
- Truncus Arteriosus — both RV and LV flow into one artery
- Tricuspid Atresia — leads to shunt through patent PFO, RV is non-functional)
- Total Anomalous Pulmonary Venous Connection (TAPVC) — APO results from obstructed pulmonary venous drainage, PGE1 doesn’t work for this
Other
- Pulmonary atresia (absent connection between RV and PA) is also a rare cause of cyanotic congenital heart disease)
- Eisenmenger’s syndrome (an acyanotic lesion causing left-to-right shunt can lead to pulmonary hypertension if untreated, the raised PA pressures ultimately cause shunt reversal and cyanosis)
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