Blood and transfusions Flashcards
How did history bring us to modern blood transfusions?
Hippocrates came up with the four humors: blood, phelgm, yellow and black bile.
Leeches were used as blood-letting.
William Harvey described the circulation system.
Richard Lower performed the first transfusion in a dog.
Jean Baptiste Denys performed a xenotransfusion.
James Blundell performed first obstetric transfusion.
Karl Landsteiner discovered ABO groups and Rhesus factor to safely tranfuse blood without rejection.
What are the features of red blood cells?
Red blood cells take 60 secs to complete one full cycle of circulation.
Red colour due to iron molecules in haemoglobin.
Carry on their surface 400 different antigens, ABO and Rhesus are the important ones.
What are antibodies?
A protein produced by B cells which bind to antigens on RBCs.
Made up of an antigen-binding sites, a light chain and a heavy chain.
Can be IgG, IgE, IgD (Y-shaped) or IgM and IgA (much bigger with varying shapes).
Sometimes called agglutinins because they cause agglutination.
What causes a transfusion reaction?
Patient transfused with RBC (and antigen on cell surface) that they lack on their own RBC.
Production of antibodies reacting with that antigen.
Leads to a transfusion reaction.
What are the ABO antibodies?
Naturally occuring antibodies from 6 months of age.
No previous transfusion/pregnancy needed.
A and B are most important (usually IgM).
React optimally at cold temperatures (4 degrees).
Present in plasma.
What are immune antibodies?
Usually IgG, can be IgM.
Given by transfusion or trans-placental passage in pregnancy.
React optimally at warm temperatures (37 degrees).
Most important is Rh antibody anti-D.
What is the Rh system?
Most important are the D, C, E, e antigens.
Encoded by 2 genes on chromosome 1.
Group of Rh genes are inherited from each parent (haplotype).
Mostly through immune transfusion/pregnancy.
D is responsible for most clinical issues.
Can be present (Rh D+) or absent (Rh D-).
What’s the danger with anti-D and pregnancy?
In women who are Rh D- with dd genotype with a baby who carries paternal antigens such as D.
If D- mother exposed to D+ baby’s RBCs, IgG anti-D antibodies are produced by the mother.
Anti-D can cross placenta and hemolyse baby’s red cells.
SO anti-D is given to all Rh D- mothers to prevent production of antibodies (sensitisation).
How is donated blood separated out?
Donated on a voluntary basis via NHSBT
Whole blood is separated out into fresh plasma, buffy coat and red cell concentrate.
Fresh plasma can be used to correct coagulopathy, or fractionation of albumin, gammaglobulin, anti-viral immunoglobulins and coagulation factors. Can also be used for cryoprecipitate (source of fibrinogen) and platelets.
How are blood donors selected?
17-70 years old, greater than 50kg.
Hb is greater than 134 in men and 120 in women.
12 weeks in between.
Deferred post-piercing, tattoo, acupuncture, paid sex, homosexual act, live vaccinations.
Travel history considered for risk of infections.
What is group and save and crossmatch testing?
Group and save aims to reduce the risk of acute hemolytic transfusion reaction by telling us the ABO group and Rh status by screening the serum for antibodies.
Crossmatch testing, tests the donor blood against patient blood by mixing and incubating at varying temps. Looking for agglutination visually or microscopically.
What are the early and late transfusion risks?
EARLY
ABO incompatibility, allergic reaction, pyrogenic reaction, bacterail contamination, coagulopathy, circulatory overload, transfusion related acute lung injury, post transfusion purpura.
LATE
RhD sensitisation, delayed transfusion reactions, transfusion related iron overload, viral and prion infections.
What are the alternatives to blood transfusion?
Oral or IV iron
Stop antiplatelets and anticoagulants
Intra-operative cell salvage and re-infusion
EPO injections
What blood products can we transfuse?
- Packed red cells: plasma-depleted, can be given with diuretic, infusion over 2-3 hours through cannula.
- Platelets: stored at room temp, given as 1 adult pool over 30mins, aim for platelet count as >10.
Given for thrombocytopenia, disordered platelet function and bleeding. - FFP: stored at -30, frozen within 6 hours, contains coagulation proteins and inhibitors. Given for massive transfusion and dilutional coagulopathy, liver disease, disseminated intravascular coagualation.
- Cryoprecipitate: rich in fibrinogen (factor I), used in massive transfusion and DIC.
What factor concentrates might we want to give to a patient?
- Specific clotting factors. FVIII for haemophilia A and FIX for haemophilia B.
- Pooled immunoglobulin for immunodeficiencies and many other indications.
- Human albumin solution used to increase osmotic pressure and can reduce oedema. Used for paracentesis, plasmapheresis, spontaneous bacterial peritonitis.
