Blood transfusions - science and clinical practice Flashcards
How are A and B antigens made?
by action of transferase enzymes on H, adding either:
- N acetyl galactosamine (A)
- galactose (B)
What is the bombay group?
they are a very small group of people that don’t have H antigens -
have anti-H abs
- therefore they can’t be given any of the ABO blood groups
Why is ABO blood groups the most important?
1) people who don’t have the antigen have the corresponding Ab => only way you make the Ab is if you are exposed to the antigen whereas in ABO this doesn’t happen
2) type of antibody
= anti A /B = IgM => core important function of it id very sticky therefore activates complement on its own => immediate lyse if need too
What is the % distribution of the different ABO blood groups in the UK?
O= 45%
A= 43%
B=9%
AB = 3%
O= universal donor AB= universal recipient
What are the “other” blood groups?
Rh "rhesus" - C c D E e Kell - 90% of pop are kell -ve Duffy - Fya Fyb Kidd - Jka Jkb M N S s these are the key other ones that are tested for in group and save test - these are generally IgG antibodies
What are the key characteristics of IgG antibodies?
stick to foreign particles
facilitate their destruction in the spleen
engulfed by macrophages
slow process
What are the key characteristics of IgM antibodies?
stick to foreign particles
cause immediate activation of complement
occurs in blood vessels
acute and dramatic process
What does it mean by forward blood group?
at the blood banks they are looking at antigens on red cell surface to help identify what blood group someone is
Why do antibodies usually form?
naturally e.g. anti- a/b
transfusion
pregnancy
How much incorrect blood (group) can kill a person?
10ml e.g. giving A to O - haem is very nephrotoxic
Where does blood come from?
All comes from blood donors - static donor centres and blood mobile centres
How often can blood donors donate?
M- every 12 weeks
F - every 16 weeks - more likely to be iron deficient
Why is blood depleted of leucocytes?
because it reduces risk of CJD
How are red cells stored? How long should they be transfused over ?
stored at 4 degrees with a shelf life of 35 days (only be out of storage for 30 mins)
transfuse over 2-3 hours
plasma reduced; optimal additive solutions - SAGM
How do you mitigate transfusion overload?
transfuse the blood slowly however youve only got 4 hours to transfuse it over
Why are red cells stored at 4 degrees?
reduce risk of proliferation of bacteria if contaminated
What is meant by a-foresis platelets?
take red cells out and add different ones
What is the single dose of platelets given? How are platelets stored and how long can they be transfused over?
dose = 1 unit platelets (4WB donations or 1 apheresis)
stored at ambient temperature of 22 degrees with a shelf-life of 7 days - if they are stored in the fridge the platelets are more active
transfuse over 30 to 60 minutes
Which patients get the majority of platelet donations?
chemo patients to help mitigate bleeding
What is a normal dose of plasma and how is it stored?
FFP - stored frozen; allow 30 mins to thaw
12-15ml/kg; 3-4 units per dose
used to correct deranged clotting - relatively dilute way of giving clotting factors
can be kept in a freezer for 3 yrs
What are the universal donor products (red cells, plasma, platelets)?
red cells = O Rhd negative
plasma = AB (A) - struggle to give AB because its so rare- anti-B reaction is less of a problem than anti-A therefore giving A plasma is generally fine
platelets = AB RhD neg (A) - A is much more common
What are the universal recipient products (red cells, plasma, platelets)?
red cells = AB RhD pos
plasma = O
platelets = O RhD neg
What questions need to be considered when deciding whether or not to transfuse someone?
- why are they anaemic/thrombocytopenic/coagulopathic?
- what else can be done to correct it?
- how long will that take? Can we wait?
- are they bleeding?
- are you giving prophylaxis or treatment ?=> platelet transfusion to reduce risk of bleeding
When in iron deficiency do you do a blood transfusion?
only transfuse if they are at high risk of cardiac event or very dizzy
What are the triggers for red cell transfusion?
dose - approx increment of 10g/L per unit for an average 70kg adult
- acute blood loss with haemodynamic instability
- Hb <70g/L stable patient
- Hb <80g/L if cardiovascular disease
- chronic transfusion dependent anaemia (Hb threshold <80g/L initially, but adjusted to patient)
rare that you need to give more than one unit
What are the triggers for platelet transfusion?
dose - 1 unit (should increase platelet count by 30)
- prophylactic platelet transfusion
- prior to invasive procedure or therapy =only lasts for a few days so give as close to surgery as possible
- therapeutic use to treat significant bleeding
- specific clinical condition
- platelet dysfunction
our normal platelet count is 150-400 so there is a massive reserve
What are the triggers for fresh frozen plasma transfusion?
dose - 15ml/kg body weight - often equivalent to 4 units in adults
- major haemorrhage
- PT ratio/INR <1.5 with bleeding
- PT ratio /INR <1 and pre-procedure
- Liver disease with PT ration/INR <2 and pre-procedure
use in preventing bleeding is minimally justified
What are the triggers for cryoprecipitate transfusion?
dose - 2 pooled units equivalent to 10 individual units, will increase fibrinogen by approx 1g/L
- clinically significant bleeding and fibrinogen <1.5g/L
- fibrinogen <1g/L and pre-procedure
very high MW stuff
What is the process of taking someones blood?
1) positively identify the patient
2) check details against their wristband
3) obtain verbal consent
4) draw sample
5) label the sample by hand at the bedside
6) check the labelled sample against the wristband
What is classed as major haemorrhage?
loss of more than one blood vol within 24 hours (around 70ml/kg , >5L in 70kg adult)
50% total blood vol lost in less than 3 hours
bleeding in excess of 150ml/L
What should you do in the instance of major haemorrhage?
give red cells + plasma = outcome is better
- 4 units red cells + plasma
What is tranexamic acid?
it is a clot stabiliser and used in major haemorrhage to prevent fibrinolysis
What are the IMMUNE adverse effects of transfusion?
wrong blood
febrile non-haemorrhagic transfusion reaction =>give unit of blood get a bit of a temp, its fine, just slow transfusion and give paracetamol
allergic- tends to be more common with plasma
PTP
TRALI
TA-GvHD
immunomodulation
What are the INFECTIOUS adverse effects of transfusions?
viral bacterial, syphilis parasites prions ?new agents in future
What are the OTHER adverse effects of transfusions?
iron overload fluid overload (TACO)
What are the top 3 serious risks with transfusions and what are the top 3 commonest?
serious
1) ABO incompatibility
2) bacterial infection
3) anaphylaxis
common
1) TACO
2) FNHTR
3) Allergic
What are the top 3 serious risks with transfusions and what are the top 3 commonest?
serious
1) ABO incompatibility
2) bacterial infection
3) anaphylaxis
common
1) TACO
2) FNHTR
3) Allergic
biggest risk to patients is that a healthcare professional will make a mistake
What are the risky bacterial infections that could arise?
bacterial sepsis => especially if a bacterial endotoxin is produced e.g. E.coli
hypotension, fever, tachycardia within mins of starting the transfusion
acquired from donor skin - reduced risk by stringent cleaning of skin, divert pouch and bacterial screening
it can be fatal
What element is critical at all stages of a blood transfusion?
patient identification - ask the pt, check the wristband, check the blood label, check the prescription chart, check the notes
When should the first set of observations be checked after starting a blood transfusion?
baseline
15 minutes
end of transfusion
What pulmonary complications can arise from transfusions and who is at risk?
Transfusion associated circulatory overload (TACO) pts at risk: - elderly - pre-existing disease - low weight pts given large vol transfusions - renal impairment - liver impairment - concomitant fluids - diuretic use
What is TRALI?
Transfusion related acute lung injury (TRALI)
- transfused ab in donor pts interact with white cells
What is acute haemolytic reaction?
due to ABO mismatch
- can be fatal soon after starting transfusion
- immediate complement mediated red cell lysis due to IgM anti-A/B
- hypotension, tachycardia, fever, renal failure, DIC, death
- as little as 10ml can be fatal
How is acute haemolytic reactions prevented/reduced?
2 sample rule
strict protocol when taking samples, transporting and administering blood
