You ask, we deliver!

One of you second years asked me on Monday if I could be a little clearer on the whole “You can only tell the patient is cyanosed if they have enough haemoglobin, and not too much either” thing.

Well, the imps have dreamt up a wee flash object to demonstrate the concept…… here

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3 Comments on “You ask, we deliver!”

  1. laura Says:


    Can i just confirm that i have the right understanding of the above?
    Basically, with a PO2 of 7 you’d expect to see cyanosis due to hypoxia? However, this can be masked if anaemia or polycythaemia are present.
    I.e. With Hb of 18 – patient would look red despite a low PO2 of 7 leading you to believe they’d look blue?
    And in reverse – with a Hb of 6, patient would appear white / pallor / anaemic – despite the same low PO2.

    If the above is correct – thanks very much for the wee flash object – it clearly helped me!

    • dundeechest Says:

      Essentially you are right, and the wee Flash object has helped!

      If you want to get technical:

      Oxygenated Haemoglobin is RED
      Deoxygenated Haemogobin is BLUE
      Lack of blood is WHITE.

      So if the patient is polycythaemic, and hypoxaemic, it depends on the proportion of deoxygenated vs oxygenated haemoglobin as to how red/blue/purple they will look.

      But to keep it simple – always the best policy. You’re right.

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