Cyanosis is a blue-purple discolouration of the skin or mucous membranes. Oxygen is carried in the blood bound to haemoglobin as oyxhaemoglobin, with one oxygen molecule bound to each of the 4 polypeptide groups on the haemoglobin molecule. When oxygen molecules are released from oxyhaemoglobin, deoxyhaemoglobin is formed. Oxyhaemoglobin is bright red in colour but darkens as it loses oyxgen, becoming purple when most of the oyxgen is lost. This is why venous blood is darker than arterial blood and it is this purple deoxyhaemoglobin that causes the skin colour changes in cyanosis. The skin and mucous membranes appear blue when the amount of deoxyhaemoglobin in the blood exceeds 5g/dL.
Cyanosis normally develops when oxygen saturation drops to 85%. However, anaemic patients will not become cyanotic until their oyxgen levels drop much lower, due to their decreased amount of haemoglobin. Likewise, polycythaemic patients will become cyanosised at higher levels of oxygen saturation.
Central cyanosis is seen on the tongue and lips. The most common causes are:
Peripheral cyanosis can be a result of the causes of central cyanosis or can occur in isolation. Common causes of peripheral cyanosis without central cyanosis are:
Mr Craig, a 68 year old man, presents to A+E with a 3 day history of increasing shortness of breath and a cough producing green coloured sputum. He says his wife commented that his lips looked "a bit blue."
Imporant points in the history in a cyanosed patient are:
Mr Craig tells you his cough started 3 days ago and he has been getting progressively more breathless since then. He denies any haemoptysis or chest pain. He was diagnosed with COPD 6 years ago and takes Symbicort 2 puffs twice daily. He also takes simvastatin 40mg. He is a retired postman and lives with his wife, who is well.
On examination, his respiratory rate is 26/min, his pulse is 82/min and his oxygen saturation is 86%. He is using accessory muscles in his neck and is centrally cyanosed without peripheral cyanosis. There is reduced air entry on the right side and wheeze throughout. Apex beat is not displaced and heart sounds were normal. There was no ankle oedema.
What investigations should be carried out?
Bloods and microbiology
Mr Craig's arterial blood gases show he is hypoxic and hypercapnic. His full blood count shows a raised haemoglobin and haematocrit. Chest x-ray showed consolidation of the right lower lobe.
How would you manage Mr Craig?
Patients with cyanosis may be very unwell so an ABC approach is essential.
Mr Craig is commenced on 28% oxygen through a Venturi mask. He is started on nebulised bronchodilators, oral prednisolone and oral antibiotics according to local protocol. He recovers and is discharged 5 days later.
Pocock G, Richards CD; Human Physiology: The Basis of Medicine, 2nd edition; Oxford Core Texts; 2004. P261
http://www.patient.co.uk/doctor/Cyanosis.htm Accessed on 21/04/12
Central cyanosis image:
http://emedicine.medscape.com/article/303533-overview#aw2aab6b2 accessed on 21/04/12
Peripheral cyanosis image: http://lifeinthefastlane.com/wp-content/uploads/2011/01/Raynuads2-590x384.jpg accessed on 21/04/12
http://upload.wikimedia.org/wikipedia/en/0/0e/Outline-body.png Accessed on 21/04/12
Chest x-ray: http://emedicine.medscape.com/article/297664-workup#a0756 Accessed on 21/04/12
Douglass G, Nicol F, Robertson C; Macleod's Clinical Examination 11th edition; Churchill Livingstone 2005. p121
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