Cyanosis

Question 1

What is cyanosis?

Answer 1

Cyanosis is the result of deoxygenated haemoglobin (Hb) or abnormal Hb in red blood cells (RBCs).

Cyanosis is apparent when there is 4g/dL of reduced Hb or 0.5g/dL of methaemoglobin. Anaemic patients may not become cyanosed, even in the presence of marked SpO2 desaturation. In light-skinned patients, cyanosis is usually noted with SpO2 <85%.

Question 2

Where is central and peripheral cyanosis best observed?

Answer 2

Central cyanosis is best seen in the tongue. All peripheral areas (lips, perioral area, fingers, nose) will take on a blue hue in the presence of central cyanosis. However, they are also (and very commonly) sensitive to ambient temperature and/or peripheral vasoconstriction unrelated to deoxygenated Hb levels.

Question 3

What examinations need to occur in a cyanotic child?

Answer 3

A full assessment of cardiovascular, respiratory, and gastrointestinal (GI) systems will be needed to identify the cause.

If a cause is not found, prompt investigation (e.g. analysis of methaemoglobin) is important.

Acute cyanosis is often life-threatening.

Question 4

What causes clubbing?

Answer 4

This sign may be present in the older infant or child and indicates long-standing cyanosis in CHD, but other paediatric causes include:

• Hereditary
• Idiopathic
• Cyanotic CHD
• Infective endocarditis
• Pulmonary conditions
  
  • CF
• GI disease
  
  • Crohn’s disease (CD), ulcerative colitis (UC) and cirrhosis

Question 5

What causes cyanosis?

Answer 5

Causes can be categorised broadly as:

• Pulmonary impaired gas exchange:
  
  • Alveolar hypoventilation
  • Ventilation–perfusion inequality
  • Impairment of O2 diffusion
• Cardiovascular pump misdirection: right-to-left shunt
• Haematological: ↓ affinity of Hb for O2

Question 6

Give differentials for cyanosis

Note: alveolar hypoventilation

Answer 6

• CNS
  
  • Seizures, cerebral oedema, haemorrhage, infection, hypoxia/ischaemia and drugs
• Hypothermia

Question 7

Give differentials for cyanosis

Note: ventilation–perfusion inequality

Answer 7

• Lung
  
  • Bronchiolitis, pneumonia, pneumothorax, pleural effusion and respiratory muscle dysfunction (e.g. muscular dystrophy, myasthenia gravis, Guillain–Barré syndrome (G-BS))
• Cardiac
  
  • ↓ pulmonary blood flow: tricuspid atresia, pulmonary atresia with intact ventricular septum, critical pulmonary stenosis and tetralogy of Fallot (ToF)
  • ↓ systemic perfusion: coarctation of the aorta (CoA) and sepsis

Question 8

Give differentials for cyanosis

Note: impairment of oxygen diffusion

Answer 8

• Lung
  
  • Bronchopulmonary dysplasia (BPD), hypoplasia and diaphragmatic hernia

Question 9

Give differentials for cyanosis

Note: right-to-left shunting

Answer 9

• Cardiac
  
  • CHD, Eisenmenger syndrome and AV fistula (pulmonary or systemic)
• ↓O2 affinity for Hb
  
  • Methaemoglobinaemia: measured by blood gas analyser- may be hereditary or toxin-mediated (e.g. aniline dyes, nitrobenzene, azo compounds and nitrites)
  • Carboxyhaemoglobinaemia: usually related to smoke inhalation (hyperoxygenate until resolution)