Blood Transfusion 1 Flashcards
What is the prevalence of RhD positive patients?
85% of population carry RhD antigen
Can receive RhD -ve (just a waste!) or RhD +ve red cells
What is the prevalence of RDh negative patients? What blood should they not be given?
15% of population lack RhD antigen
Patients can make immune anti-D if exposed to RhD +ve red cells
What are immune anti-D antibodies?
IgG (so cross placenta)
Do not cause direct agglutination of RBCs
Cause delayed haemolytic transfusion reaction.
There are some other Rh antigens e.g., C, c, E + e
What are the other blood groups antigens?
Kell (K), M, N, S, Duffy (Fy), Kidd (Jk)
But only match for these if patient has corresponding antibody
Who can RhD negative cells be given to?
Can safely be given to anyone, but often in short supply.
Occasionally (emergency/ shortage) may be necessary to give RhD +ve blood to RhD -ve patients, this does not cause acute problems but sometimes induces formation of anti-D.
Will be picked up by the lab next time they need blood. RhD -ve blood would then be issued.
What RhD reaction may occur in pregnant women?
RhD -ve women exposed to RhD +ve blood can produce immune anti-D, which can cause haemolytic disease of the newborn or severe foetal anaemia + heart-failure (hydrops fetalis) in future pregnancy.
What are the immune antibodies involved in blood transfusion?
IgG
What is antibody screening and what is screened?
Can’t test all RBC antigens (100s)
but ~1-3% of patients have immune RBC antibodies to >,1 RBC antigen as a result of TRANSFUSION +/- PREGNANCY.
REALLY IMPORTANT to identify clinically significant RBC antibodies + transfuse RBCs that are -ve for that antigen to prevent a DELAYED HAEMOLYTIC TRANSFUSION REACTION. (>24h)
How does antibody screening occur?
Use 2-3 reagent red cells containing all the important red cell antigens between them.
Screen by incubating the patient’s plasma + screening cells using IAT technique.
What is the IAT technique?
Indirect antiglobulin technique.
Bridges red cells coated by IgG, which can’t themselves bridge 2 red cells – to form a visible clump. Takes 30 mins’ incubation at 37°C.
Why does antibody screening happen before every transfusion even if it might have been done before?
Because new antibodies can be made after a transfusion or in pregnancy.
What is electronic issue?
The selection + issue of red cell units where compatibility is determined by IT system, without physical testing of donor cells against patient plasma.
What are the advantages of electronic issue?
Quicker
Fewer staff
No need to have blood “standing by” just in case
Remote issue
Better stock Mx
What is serological crossmatch? Describe the indirect anti globulin technique for this
Full crossmatch:
Patient plasma incubated with donor red cells at 37C for 30-40 mins, will pick up antibody antigen reaction that could destroy the red cells + cause extravascular haemolysis.
Add antiglobulin reagent (AHG). IgG antibodies can bind to RBC antigens but do not crosslink so AHG reagent is added.
Agglutination/ haemolytic = incompatible
What crossmatching technique is used in acute need/ trauma cases?
Immediate spin technique
Saline, room temperature.
Incubate patient plasma + donor red cells for 5 mins only + spin, will detect ABO incompatibility only.
IgM anti-A +/- anti-B bind to RBCs, fix complement + lyse the cell.
What are donor RBCs labelled with?
ABO + D type
Kell
Other Rh antigens
Traceability tag
What are the three pillars of patient blood management?
Optimise haemopoiesis
Minimise blood loss + bleeding
Harness + optimise physiological tolerance of anaemia
What are steps which can be taken to achieve each of the three pillars of patient blood management?
Minimise blood loss + bleeding:
* Stop anticoagulation/ antiplatelet agents
* Blood sparing techniques
* Tranexamic acid
* Cell salvage
Harness + optimise physiological tolerance of anaemia:
* Optimise cardiac output
* Restrictive transfusion threshold
What is the decision to transfuse based on?
Is the patient bleeding?
What are the blood results?
Is patient symptomatic?
Will a transfusion solve the problem?
What are the risks of transfusion?
Are there alternative tx?
What information needs to be given for patient consent?
“Valid” consent is required for transfusion (verbal + written).
Alternatives should be considered if appropriate:
- Iron / B12 / EPO / Folate
- Cell Salvage
If transfused in an emergency, patient must be informed afterwards.
Involve patients in the process to ensure they get the right blood + the right ‘special requirements’.
What information is kept about the donor records for blood transfusion?
All components are issued on a named patient basis 100% of components must be traceable from the donor to the recipient.
Records are kept for 30y.
How are red cells given/stored?
Give ABO/D compatible.
Group O (-ve) in emergency.
Stored at 4C for 35d.
Must be transfused within 4h of leaving fridge.
Transfuse 1 unit RBC over 2-3h.
How are platelets given/stored?
ABO/D antigens weakly expressed.
Should be D compatible.
If group O given to A, B or AB patients select ‘high-titre’ -ve (anti-A/B antibodies).
Stored at 20C for 7d.
Transfuse 1 unit of platelets over 20-30 mins.
How is fresh frozen plasma given/stored?
Give ABO compatible (D group does not matter).
AB plasma can be given to all groups as it has no anti-A/B antibodies but it is in short supply.
No need to X match but does take 30-40 mins to thaw.
Once thawed can be kept at 40C for 24h.
Transfuse 1 unit over 20-30 mins.
How is cryoprecipitate given/stored?
Give ABO compatible (D group does not matter).
AB plasma can be given to all groups as it has no anti-A/B antibodies but it is in short supply.
No need to cross match but does take 30-40 mins to thaw.
Once thawed has to kept at room temperature + use within 4h.
Transfuse 1 unit over 20-30 mins.
Which blood component has a higher risk of carrying infection? Why?
Platelets- stored at a warmer temperature
What is the Maximum Surgical Blood Ordering Schedule (MSBOS)?
Agreement between surgeons + transfusion lab about predictable blood loss for ‘routine’ planned surgery. Junior docs / nurses doing pre-admission clinics have some idea what is normal.
Have to be flexible if non-standard surgery or special patient requirements (e.g. bleeding disorder). Some operations rarely need blood e.g. gall bladder op. Some operations always need blood e.g. aortic aneurysm repair.
Blood allocated to a patient, if not used are taken back into stock repeatedly.
What is a group and save in elective surgery?
If no antibodies present, sample saved in the fridge.
If unexpected need for blood, can provide it within 10 mins (by EI, as no antibodies present).
What is a crossmatch in elective surgery?
If hx of antibodies or G+S picks up new antibody.
Ensure BT lab aware of date of surgery so that suitable RBC units are available.
What are specific transfusion indications for red blood cells and their triggers?
Major Blood Loss: If >30% Blood volume lost
Peri-Op, Critical Care: Hb <70g/L vs 80g/L
Post Chemo: Hb <80g/L
Symptomatic anaemia: Ischaemic heart disease, breathless, ECG changes.
What are things to be careful about when giving a blood transfusion?
Check Hb pre transfusion + after every 1-2 units.
1 unit RBC gives a Hb increment of 10g/L in a 70-80 kg patient.
Transfusion to >100g/L is rarely required, unless symptomatic or severe cardiac/ resp disease etc.
What are specific transfusion indications for platelets and their triggers?
Massive transfusion: Aim Plts >75 x109 /L
Prevent bleeding (post chemo): If < 10 x109 /L (<20 if sepsis)
Prevent bleeding (surgery): < 50 x109 /L (<100 if critical site: eye, CNS, polytrauma)
Platelet dysfunction or immune cause: Only if active bleeding
What are things to be careful about when giving a platelet transfusion?
1 unit of platelets is an adult tx dose: Usually raises platelet count by 30-40 x109 /L.
Platelets are best given whilst procedure being carried out, little/ no benefit in giving earlier on ward.
When is a platelet transfusion contraindicated?
Heparin-induced Thrombocytopenia Thrombosis (HiTT)
Thrombotic Thrombocytopenic Purpura (TTP)
What are indications for FFP indications and dosage?
Massive transfusion early infusion of FFP is recommended to treat coagulopathy. Aim to maintain PT + APTT ratio at <1.5.
Liver disease: No evidence of benefit from FFP in patients with a PT ratio of ,< 1.5.
Replacement of single coagulation factor deficiency, e.g. factor V.
DIC in the presence of bleeding + abnormal coagulation results.
Thrombotic thrombocytopenic purpura (TTP).
4 units in 70kg man.
What is in cryoprecipitate?
Fibrinogen
fVIII + vWF
Fibronectin
fXIII
Platelet microparticles
IgA
Albumin
Can someone receive their own blood if they are a donor?
Pre-operative autologous deposit: Donate own blood before planned operation. Not in UK (futile, no net gain + doesn’t avoid problems of wrong blood or bacterial contamination).
Intra-operative cell salvage: Yes - Collect blood lost during surgery: centrifuge, filter, wash + re-infuse it. Most UK surgical + obstetric units can do this.
Post-operative cell salvage: Collect blood lost post-op into wound drain – filter + re-infuse. Mainly ortho (knee surgery).
Why might those receiving cell salvage blood need other components?
All coagulation factors + platelets are removed
What are specific requirements for a blood transfusion?
CMV -ve blood: Only required for intra-uterine/ neonatal transfusions + for elective transfusion in pregnant women (baby in-utero is exposed to maternal transfusion).
Irradiated blood: Required for highly immunosuppressed patients, who can’t destroy incoming donor lymphocytes: which can cause (fatal) transfusion associated GvHD (TA-GvHD).
Washed: Red cells + platelets are only given to patients who have severe allergic reactions to some donors’ plasma proteins.
