Transfusion Medicine

• The four main blood components:

  • Red cells
  • Platelets
  • Fresh frozen plasma
  • Cryoprecipitate
• Red cells - what is in the bag:

  • After the blood is centrifuged, packed red cells will be at the bottom of the blood bag
  • Optimal additive solution is added to them so that the bag will last for 28-35 days before it expires if refrigerated properly
• Red cells - when should they be used:

  • Use them to top up people who don't have enough red cells - eg anaemic patients
  • In pts with major injuries with significant blood loss
  • Only really transfuse red cells when it's really needed/it would be a good benefit to the patient
• Red cells - special considerations:

  • Less is more (generally) in stable patients - don't need to transfuse just to get haemoglobin count up
  • Possible exceptions in cardiac, paeds, haem
  • Restrictive thresholds in most settings
• Platelets - what is in the bag:

  • Platelets - sit in platelet additive solution
  • Either produced in a pool - whereby 4 platelet donations are taken from 4 separate whole blood donations to 4 separate donors, and then the platelet layer is added together; you need 4 in order to make a single pool of platelets - or by a machine removing just platelets from the patient, which is good; since not taking red blood cells or plasma, can collect enough from 1 donor for 2-3 single adult therapeutic doses
• Platelets - should be used when patient's platelet count is low, especially if that patient is bleeding.
• Platelets - special considerations:

  • Recent BSH Guidelines (2016)
  • Threshold of 30x10⁹/L for non-severe bleeding
  • 50x10⁹/L for severe/life threatening
• FFP (fresh frozen plasma) - what's in the bag:

  • Plasma - the soup that your red blood cells sit in when they're circulating around the body
• FFP (fresh frozen plasma) - when it should be used:

  • Major use = to replace and correct clotting factor deficiency - plasma has lots of clotting factors in it, as well as fibrinogen which is the raw material for making blood clots
  • Used in a protocolised way for major bleeding/massive haemorrhage, where it's given alongside red cells to replace blood that's being lost actively
• FFP (fresh frozen plasma) - special considerations:

  • Has to be thawed (takes 15-30 mins) - therefore not instantly available - although most trauma units will have a thawed back on hand in case of emergencies
  • Volume considerations - 1 unit is around 250ml but a therapeutic dose for an adult is 1 litre (4 units) - significant load for patient
• Cryoprecipitate is a concentrated fibrinogen product (along with a few other clotting factors).
• Cryoprecipitate - when it should be used:

  • When people have low fibrinogen levels
  • Given in a protocolised way in major haemorrhage protocols
• Cryoprecipitate - special considerations:

  • Has to be thawed (again takes about 15-30 mins)
  • Should be thought of early in major haemorrhage - not just when fibrinogen level has gone v low - fibrinogen part of clotting cascade is right at the bottom, so it's the final common pathway - if you don't have fibrinogen, you can't make fibrin, which is the meshwork that makes a blood clot, so if you don't have fibrinogen then you can't stop bleeding; can't form a blood clot
• Immunological risks of transfusion:

  • Febrile - odd things in the plasma that belong in the donor, and when put in the patient can cause them to have a bit of an immunological response to them - pretty normal - can be managed by stopping transfusion, giving paracetamol and then restarting more slowly
  • Allergic - mild allergic reactions are not uncommon - sometimes people can feel itchy/get hives - can usually be treated with antihistamines though
• Immunological risks of transfusion:

  • Alloimmunisation - much less frequent but more important complication - sometimes pt can form antibodies against an antigen on foreign red blood cells that their body doesn't recognise - therefore next time around, the antibody in their system will stop them from being able to receive any blood with that same antigen present - ok most of the time; people tend to only need 1 transfusion
• Immunological risks of transfusion:

  • Alloimmunisation - sometimes pt can form antibodies against an antigen on foreign red blood cells their body doesn't recognise - next time around, the antibody in their system will stop them from being able to receive any blood with that same antigen present - important for women; if they develop an antibody then become pregnant, that antibody can cross over through the placenta (because most of these antibodies will be IgG antibodies). If the foetus expresses the antigen that antigen has been formed against - can cause haemolytic disease of the foetus
• Circulatory risks of transfusion - transfusion-associated circulatory overload (TACO):

  • Similar to heart failure producing pulmonary oedema, but not the same as someone becoming overloaded with saline if they get lots of fluid on the ward/having too much fluid in a resuscitation - specific to transfusions
  • Although a red cell unit may only be quite a small volume, it has a big effect within the circulating volume of a pt
  • Elderly pts, pts with low albumin, renal failure or low body weight more vulnerable to this
  • One of the commonest reasons for severe transfusion complications
• Circulatory risks of transfusion - infection (rare complication):

  • Bacterial infection - usually something associated with platelet transfusions; platelets are stored at room temp rather than in the fridge, which gives a slight advantage to bacterial multiplication of certain bacteria
  • Viral infection (eg HEV) - risk of catching virus from donor - donations are always screened for common transmissible viruses but there's a failure rate; high volume of transfusions -results in several pts contracting/being at risk of contracting things like hepatitis