Cyanosis: assessment
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:
alveolar hypoventilation;
ventilation–perfusion inequality;
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
·
Hypothermia
·
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
·
Carboxyhaemoglobinaemia
The key part of the assessment is
respiratory and cardiovascular.
·Record the temperature.
·Record HR.
·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:
·hereditary;
·idiopathic;
·congenital heart disease (CHD);
·infective endocarditis;
·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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