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Cyanosis is the result of deoxygenated haemoglobin or abnormal haemo-globin in the blood. Cyanosis is apparent when there is 4g/dL of reduced haemoglobin or 0.5g/dL of methaemoglobin. Anaemic patients may not become cyanotic even in the presence of marked arterial desaturation. In light-skinned patients, cyanosis is usually noted with arterial saturation <85%. In dark-skinned patients, the saturation must be lower. Cyanosis is caused by the following problems.
· Lung pump:
impairment of oxygen diffusion.
· Cardiovascular pump: right-to-left shunting.
· Haematological: decreased affinity of haemoglobin for oxygen.
· CNS: seizures; cerebral oedema; haemorrhage; infection; hypoxia– ischaemia; drugs
· Lung: bronchiolitis; pneumonia, pneumothorax; pleural effusion; respiratory muscle dysfunction (muscular dystrophy, myasthenia gravis, Guillain–Barré); tracheal compression
· Cardiac: decreased pulmonary blood flow (tricuspid atresia, pulmonary atresia with intact septum, critical pulmonary stenosis, tetralogy of Fallot); decreased systemic perfusion (coarctation of the aorta, sepsis)
· Lung: bronchopulmonary dysplasia; hypoplasia; diaphragmatic hernia
· Cardiac: congenital heart defect; Eisenmenger syndrome; AV fistula— pulmonary or systemic
· Decreased oxygen affinity for haemoglobin
· Methaemoglobinaemia: hereditary; aniline dyes; nitrobenzene; azo compounds and nitrites
The key part of the assessment is respiratory and cardiovascular.
·Record the temperature.
·Record BP in all four limbs.
·Is there evidence of failure to thrive?
This sign may be present in the older infant or child. It should be looked for in the fingers and toes. The causes can be:
·congenital heart disease (CHD);
·pulmonary conditions (e.g. cystic fibrosis);
·GI disease (e.g. Crohn’s, ulcerative colitis, cirrhosis).
In the neonate increased respiratory rate (usually <80breaths/min) with no respiratory distress suggests cyanotic heart disease, but with respiratory distress pulmonary disease is suggested. In the older child a full respiratory examination is required—look at all components of the examinations.
The absence of a murmur does not exclude congenital heart disease. Is the liver enlarged?
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