Transfusion

Understanding the adverse consequences of blood transfusion, including that of massive blood transfusion

Production and Storage of Blood Products

Red cells, platelets, and FFP have different storage requirements.

Red Blood Cells

• Stored blood decays over time - this is known as a storage lesion
  Preservatives are used to extend the time blood can be stored:
  • Kept at ~4°C (balance between freezing and being too warm)
    • Reduces cellular metabolic requirement
    • Inhibits bacterial growth
  • Collected in an aseptic fashion
  • Stored in special solutions:
    • SAGM is currently used by the Australian Red Cross:
      • Saline
      • Adenine
        Substrate for ATP synthesis
      • Glucose
        Substrate for RBC glycolysis
      • Mannitol
    • CPDA1 (citrate-phosphate-dextrose-adenine) was traditionally used
      • Citrate binds calcium, preventing clotting
      • Phosphate acts as a buffer and phosphate source for metabolism
      • Dextrose
      • Adenine

• A storage lesion describes the changes that occur in stored blood:
  • Loss of 2,3 DPG
    Less of a factor in CPDA1 blood.
  • Haemolysis
  • Hyperkalaemia
    Typically not clinically relevant as potassium is taken up into red cells when metabolism resumes.
  • Acidaemia
  • Hyponatraemia
    Not clinically significant.

• Blood can be stored for up to 35 days, which corresponds to 70% survival

Platelets

Platelets require particular storage conditions to remain functional:

• Temperature ~22°C
  Below this, platelets deform and become non-functional
• Gas exchange
  Platelets are stored in a bag which allows gas exchange to occur, minimising lactic acid and carbon dioxide production
• Agitation
  Platelets are stored on an agitator which prevents clotting and ensures the platelets are well mixed, which maximises the diffusion gradient for gas exchange
• pH control
  pH is kept between 6.2 to 7.8 to prevent degranulation.

As platelets do not contain antigen, there is not a strict requirement for platelets to be type matched. However:

• Rh(+) platelets should be avoided in Rh(-) patients
  The small amount of contaminating red cells may precipitate rhesus disease.
• Plasma incompatibility should be avoided as this may lead to haemolysis of recipient red cells
  • Children are at greater risk due to their proportionally smaller blood volume

Fresh Frozen Plasma

Fresh Frozen Plasma is:

• Prepared either via:
  • Separation from whole blood
  • Apheresis
    Removal of a large volume (typically 800ml) of plasma from a single patient, with return of red cells to the donor.
• Once collected, it is frozen and re-thawed in a water bath prior to use

Cryoprecipitate

Cryoprecipitate is prepared by removing the precipitate from FFP which forms at 1–6°C. Cryoprecipitate contains predominantly:

• Fibrinogen
• Fibronectin
• vWF
• Factor VIII
• Factor XIII

Whole Blood

Whole blood undergoes additional changes:

• White cells become nonfunctional within 4-6 hours of collection, though antigenic properties remain
• Platelets become non-functional within 48 hours of storage at 4°C
• Factor levels decrease significantly after 21 days

Blood Groups

Blood groups refer to the expression of surface antigens by red blood cells, as well as any antibody in plasma. Blood groups can be divided into three types:

• ABO
• Rhesus
• Other antibodies These are additional antibodies that a patient may express in plasma, and include Kell, Lewis, Duffy, etc.

ABO

The ABO blood group is:

• A complex carbohydrate-based antigens series
  These may be either A or B antigen, and patients may express one, both, or neither, giving four blood groups (A, B, AB, O).
• Expressed on the H-antigen stem of RBCs, and on the surface of tissue cells.
  • The Bombay Blood Group (or hh or Oh group) describes individuals who do not express the H antigen
    These individuals:
    • Don't express A- or B-antigen (as there is no H-antigen stem) and are 'universal donors'
    • Express H-antibody
      Can only receive blood from other individuals with the Bombay phenotype
• Individuals express IgM antibody to foreign blood groups
  This develops within 6 months of birth, likely due to environmental exposure to similar antigens.
• Associated with a severe hypersensitivity reaction if an ABO-mismatch occurs

Rhesus

The Rhesus blood group is the next most important group after ABO. The Rhesus system:

• Consists of ~50 different antigens, the most important of which is D
  Rhesus status is therefore expressed as positive (D - 85% of the population) or negative (anything-but-D).
• Rhesus antibody does not naturally occur in Rh(-) individuals
  • This is relevant in Rhesus disease
    A Rh(-) mother exposed to Rh(+) blood will develop Anti-D antibody, which can cross placenta and induce abortion in a future Rh(+) foetus. This can occur with:
    • Incompatible transfusion
    • Foetal-maternal haemorrhage

Compatibility Testing

Donor blood must be tested with recipient blood to avoid a transfusion reaction. This involves three steps:

• Blood Typing (ABO/Rh)
  • Patient's blood is mixed with samples of plasma known to contain Anti-A, Anti-B, or Anti-AB antibodies.
  • Agglutination occurs when antibodies in the plasma react with the antigen on the RBC surface, and indicates a mismatch
• Antibody Screen
  For minor (non-ABO/Rh) group antibodies.
  • Testing is similar to ABO screening, but now patient plasma is mixed with several samples of red cells which contain a known non-ABO/Rh antigen (e.g. Kell, Duffy), and monitored for agglutination
• Cross-match
  Two methods:
  • Electronic cross-match
    Used if the antibody screen is negative and the patient has had no previous blood transfusion, as it is quicker and cheaper.
  • Serological cross match
    Indicated if the antibody screen is positive, or the patient has had previous exposure to blood (prior transfusion, pregnancy), as this gives the patient a risk of exposure to non-ABO or Rh antigens.
    • Performed by mixing patient plasma with a small sample of donor RBC and monitoring for agglutination If there is no agglutination, the transfusion can proceed with the tested specimen only.

Indirect Coomb's Test

Method of cross-matching that is now deprecated as it provides negligible additional safety over the above processes. Testing identifies IgG antibody in host plasma which would haemolyse transfused red cells, and involves:

• Incubating
  Binds IgG Ab to antigen on RBC membrane.
• Washing
  Removes serum and unbound IgG.
• Testing with an antibody to IgG, known as antiglobulin serum.
  • A positive test will cause clumping of red cells, as each antiglobulin serum will bind two IgG molecules, which have in turn been bound to red cells
  • A negative test will cause no agglutination, as the IgG has not been bound to red cells
  • If negative, the antiglobulin serum is re-used on a control sample to ensure that it is not a false negative

Transfusion Reactions

An adverse event associated with the transfusion of whole blood or one of its components. Can be classified as either acute (< 24 hours) or delayed (> 24 hours), and as immunological or non-immunological.

Immunological Acute Reactions

Non-Immunological Acute Reactions

Delayed Immunological Reaction

Delayed Non-Immunological Reaction

Complications of Massive Transfusion

A massive transfusion is one where:

• Greater than one-half of circulating volume in 4 hours
• Whole circulating volume in 24 hours

Risk of complication from a massive transfusion is influenced by:

• Number of units
• Rate of transfusion
• Patient factors

References

1. Blood Service. Classification & Incidence of Adverse Events. Australian Red Cross.
2. National Blood Authority. Patient Blood Management Guidelines. Australian Red Cross.
3. Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.