Cyanosis
Cyanosis is the abnormal blue discoloration of the skin and mucous membranes resulting from the presence of 5 g/dL or more of reduced haemoglobin in the blood. It is not synonymous with hypoxaemia, which may be present (e.g. anaemia) without cyanosis.
History
Central cyanosis
Onset
Cyanosis due to congenital heart disease causing anatomical right to left shunts may have been present from birth or the first few years of life. Immediate onset of cyanosis may be due to pulmonary emboli or cardiac failure. Acute onset of cyanosis may be precipitated by pneumonia and asthma. Patients with COPD develop cyanosis over many years. Accompanying polycythaemia may exacerbate cyanosis in these patients.
Chest pain
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