Cyanosis

OVERVIEW

• Cyanosis is a bluish hue that occurs in the presence of ~60 g/L deoxyhaemoglobin or dyshemoglobinaemia
• the differentials include treatment with methylene blue and new clothes that leach blue ink…

CENTRAL VERSUS PERPIHERAL CYANOSIS

• perpiheral causes will not of signs of central cyanosis
• central cyanosis is suggested clinically by bluish discolouration of the tongue and mucous membranes, rather than just the peripheries (e.g. fingers and nail beds)

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 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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