Cyanosis

Cyanosis is the abnormal blue discoloration of the skin and mucous membranes. Most patients with a saturation of 90 per cent or less will appear cyanosed. Cyanosis is less marked in severe anaemia and more marked in polycythaemia. The word cyanosis comes from the Greek cyanos meaning dark blue.

Unless the cause is already established, episodes of central cyanosis required urgent assessment. This is particularly essential for infants and young children, who require urgent admission.

Cyanosis may be central or peripheral. The age of onset, speed of onset and associated features usually give a guide to the underlying cause.

• Central cyanosis in neonates:
  • Transient cyanosis after delivery: central cyanosis should clear within a few minutes of the birth. Peripheral cyanosis (acrocyanosis) clears within a few days. Increased sensitivity of the peripheral circulation to cold temperature may persist well into infancy.
  • Cardiac and circulatory causes include:
    • Transposition of the great arteries
    • Stenosis or atresia of the pulmonary artery or tricuspid valve
    • Total anomalous pulmonary venous return
    • Persistent fetal circulation
  • Respiratory causes include:
    • All causes of respiratory distress syndrome
    • Birth asphyxia, birth injury or bleed
    • Obstruction of the airway, for example in Pierre-Robin syndrome or choanal atresia
    • Other causes include seizures and metabolic abnormalities, e.g. hypoglycaemia, hypomagnesaemia
• Central cyanosis in adults:
  • Lung disease: any severe respiratory disease, pulmonary oedema, pulmonary embolism, decreased PO₂ of inspired air (e.g. high altitude), severe pneumonia, chronic obstructive pulmonary disease, acute severe asthma, acute adult respiratory distress syndrome.
  • Right to left cardiac shunt: e.g. Eisenmenger syndrome
  • Abnormal haemoglobin: methaemoglobinaemia, sulphaemoglobaemia. Do not allow adequate oxygen uptake
  • Polycythaemia rubra vera or any other cause of polycythaemia may present with central cyanosis.
• Causes of Peripheral cyanosis:
  • All causes of central cyanosis cause peripheral cyanosis.
  • Reduced cardiac output e.g. heart failure, hypovolaemia.
  • Vasoconstriction e.g. due to cold exposure, Raynaud's phenomenon.
  • Arterial obstruction e.g. thrombosis or atheroma.
  • Venous obstruction; e.g. iliofemoral deep vein thrombosis can produce a painful blue leg (phlegmasia cerulea dolens).

Symptoms

• Age and nature of 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.
  • Acute onset of cyanosis may be due to pulmonary emboli, cardiac failure, pneumonia or asthma.
  • Patients with COPD develop cyanosis over many years and associated polycythaemia may exacerbate the degree of cyanosis.
  • The description may be typical of raynaud's phenomenon.
• Associated symptoms:
  • Chest pain: cyanosis associated with pleuritic chest pains may be due to pulmonary emboli or pneumonia. Pulmonary oedema may cause dull, aching chest tightness.
  • Dyspnoea: sudden onset of dyspnoea can occur with pulmonary emboli, pulmonary oedema or asthma.
• Past history: cyanosis can result from any lung disease of sufficient severity. Certain drugs may cause methaemoglobinaemia (e.g. nitrates, dapsone) or sulphaemoglobaemia (e.g. metoclopramide).

Signs

• Temperature: pneumonia and pulmonary emboli may be associated with pyrexia.
• Inspection:
  • Central cyanosis produces a blue discoloration of the mucous membranes of the lips and tongue as well as the extremities.
  • Peripheral cyanosis affects the extremities and the skin around the lips but not the mucous membranes.
  • Clubbing may be due to congenital cyanotic heart disease or cystic fibrosis.
  • The JVP is elevated with congestive cardiac failure.
• Respiratory examination:
  • Poor chest expansion occurs with chronic bronchitis, asthma. Unilateral reduced chest expansion may occur with lobar pneumonia.
  • Dullness to percussion occurs over an area of consolidation.
  • Localised crepitation may be heard with lobar pneumonia. Crepitation is more widespread with bronchopneumonia and pulmonary oedema. Air entry may be poor with COPD and asthma. Bronchial breathing may be auscultated over an area of consolidation, and wheezing may be heard with asthma.
• Heart sounds may be abnormal or added heart murmurs may suggest a cardiac origin.
• Localised features suggesting an aetiology of peripheral cyanosis such as oedema in venous insufficiency or absent peripheral pulses and ischaemia in arterial occlusion.

• Oxygen saturation: saturation is usually below 85%
• Arterial blood gases: reduced PaO₂ with all severe lung disease
• Full blood count: haemoglobin increased with chronic cyanosis. White-cell count increased in pneumonia and pulmonary embolism.
• ECG: features of myocardial infarction; non-specific ST abnormalities with pulmonary emboli
• Chest x-ray: pneumonia, pulmonary infarction, cardiac failure
• Sputum and blood cultures: pneumonia
• VQ scan or pulmonary angiography: pulmonary embolus
• Echocardiography: cardiac defects
• Haemoglobin spectroscopy: methaemoglobinaemia, sulphaemoglobaemia
• Digital subtraction angiography: acute arterial occlusion
• Duplex Doppler or venography: acute venous occlusion