How to transfuse: The ultimate guide to giving blood to cats and dogs
Let me ask you a question.
Who does the blood transfusions in your practice? The vets? Or the nurses? Yes, it’s going to be us monitoring the patient and collecting the vitals, but who…
Calculates the blood?
Prepares it?
Performs the donations?
Cares for the donors?
If it’s not the nurses, I’m going to suggest it should be - because there’s no reason for us not to do all of these things (as long as we run our plan past the vets and ensure they agree before going ahead!)
So, my mission in this post is to take the confusion out of transfusions… and to show you just how un-scary and fun they can be!
Want more practice calculating and planning transfusions, so they’re not scary when that emergency arrives? I’m hosting a workshop in just one week where we’ll work together and do just that. You can still grab a few last-minute tickets here - so make sure you save your spot!
What are our options when it comes to blood?
There are several blood products available, and each has its indications and contraindications.
The main reason we use different blood products instead of just reaching for whole blood, is something called component therapy.
This is where we replace only what is lost. For example, if we give whole blood to a patient with IMHA, we’re giving them plasma they don’t need, which risks volume overload, and potentially increases the risk of transfusion reaction (since they could react to components within the plasma).
Using only the components we need makes each unit of donated blood go further, and avoids giving additional unnecessary blood components.
So what can we give? Well, the products commonly available for our patients (in the UK) are:
Fresh whole blood
This is blood transfused within 4-6 hours of collection from the donor. It contains all blood components; RBCs, WBCs, platelets, clotting factors and plasma proteins.
After 4 hours, platelets are considered non-viable so the only way to increase platelet levels is via a fresh whole blood transfusion.
Stored whole blood
This is whole blood which is no longer fresh. It contains all blood components as listed above, but the platelets (as well as some clotting factors) are considered non-viable due to their age.
Stored whole blood can be stored refrigerated for up to 28 days. Whole blood products are used to replace losses associated with haemorrhage or to correct anaemia with hypoproteinaemia.
Packed red blood cells
This is packed cells suspended in a very small amount of plasma, anticoagulant and a red cell nutrient mix. Packed cells are used to correct anaemias not associated with haemorrhage, or haemorrhage-associated losses if whole blood is not available. They can be stored refrigerated for up to 42 days from collection.
Plasma
This is the liquid portion of the blood after the RBCs are removed. It contains proteins and clotting factors, as well as albumin and immunoglobulin.
Fresh frozen plasma (plasma which has been separated from the red cells and frozen within 8 hours of collection from the donor) reliably contains the labile clotting factors (factor VIII, von Willebrand’s factor and fibrinogen), and so can be used for haemophilia patients, and those with von Willebrand’s disease.
Fresh frozen plasma has a year-long shelf life when stored appropriately. After 1 year, the labile clotting factors are not considered present, and the product then becomes frozen (or stored) plasma.
Stored plasma can be used for a further four years, and is used to treat coagulopathies not involving those labile factors (e.g. rat bait toxicity or hepatic failure-associated coagulopathies), and as a source of immunoglobulin in diseases such as pancreatitis and canine parvovirus.
Cryoprecipitate
This is a plasma fraction made from FFP, containing higher levels of those labile clotting factors. This is not normally routinely used in practice but is commonly used for patients with haemophilia or von Willebrand’s disease.
What about cats?
In cats, there is currently no UK feline blood bank, and so in most cases, we rely on fresh whole blood transfusions. However, it is possible to source packed red blood cells and fresh frozen plasma from overseas blood banks, if desired.
Blood typing
Blood typing identifies antigens present on the surface of red blood cells.
These antigens can cause an acute transfusion reaction when transfused into a patient with antibodies against that particular red cell antigen.
The administration of incompatible blood types can also cause the development of new antibodies, causing transfusion reactions in the future.
Canine blood groups
In dogs, there are at least 12 known red blood cell antigens, most of which are classified as Dog Erythrocyte Antigens (DEAs).
These can be present in varying combinations – so you may have a dog who is DEA 1 negative, and DEA 4 positive, for example. Testing for all 12 different antigens is not possible in practice, so we test for the one which causes the most severe reaction – dog erythrocyte antigen 1 or DEA 1.
DEA 1-negative dogs do not have the DEA 1 antigen on the surface of their red blood cells, unlike DEA 1-positive dogs.
Dogs do not have naturally-occurring antibodies against other blood groups but will develop them after their first transfusion. This means that technically you can get away without typing a dog before their first transfusion.
However, it isn’t best practice to do that – even if an acute reaction doesn’t occur, the donor RBCs may not last as long in the circulation before they are recognised as a different blood type and destroyed. It also means they create more antibodies, potentially increasing the risk of reaction to any future blood products.
Not typing patients before their transfusions can also result in excessive use of DEA 1 negative blood, leading to shortages at blood banking centres.
What about cats?
Cats have four known red blood cell antigens – A, B, AB and Mik.
Type A is the most common, type B is less common, and type AB is very uncommon.
The Mik antigen was discovered more recently and is of unknown prevalence currently. Cats are either Mik-positive or Mik-negative, and this antigen exists in combination with the A/B/AB blood group classification.
Unlike dogs, cats do have naturally occurring antibodies against other blood groups. This means that blood typing is especially important in cats.
Type B cats cannot have type A blood - since they have high levels of antibodies against A blood, this will result in a potentially fatal transfusion reaction.
Type A cats have low levels of antibodies against type B blood, and type AB cats do not have antibodies against either type A or type B blood.
Mik cannot currently be tested for in UK practice, and therefore the only way to minimise a Mik-associated transfusion reaction is by cross-matching the donor and recipient prior to transfusion.
How does crossmatching differ from typing?
Unlike blood typing which examines blood groups to minimise the risk of a reaction, cross-matching mimics a transfusion outside of the body, directly assessing if two individuals’ blood cells/plasma is compatible when mixed.
It is one of the most important procedures which can be performed to reduce the likelihood of a transfusion reaction. Cross-matching can be performed in two ways:
The major cross-match combines donor red blood cells (or whole blood) and recipient serum or plasma, to detect a major transfusion reaction associated with reactions to the donor’s red blood cells.
The minor cross-match combines the donor’s plasma or serum with the recipient’s red blood cells and is performed to detect reactions to components within the plasma.
Usually, a major cross-match is enough, since this looks for acute reactions associated with the donor’s red cells being rapidly destroyed.
You’ve got your blood… so now let’s prep!
Step one: calculating transfusion requirements
The first thing we need to do is figure out how much blood our patient needs. We do this using this formula:
Put simply, we are looking at what the patient’s normal blood volume is, multiplied by the amount we want to increase their PCV by, divided by the PCV of the blood product you’re giving.
This tells us how much of this particular bag of blood our patient needs, to increase their PCV to the target figure.
The normal blood volume is a species-specific constant and is approximately 85-90ml/kg for dogs and 60-65ml/kg for cats.
We ideally want to give the whole transfusion over about 4 hours. This is because the risk of bacterial contamination increases the longer a blood product is broached - because they contain no preservatives.
In patients with cardiac or renal disease or those at risk of volume overload, the transfusion may have to be given over a longer period (ideally not over 6 hours, if possible, due to the risk of contamination).
Preparing the transfusion
There are two main things we need to think about when preparing blood for transfusion - aseptic technique and careful handling.
If defrosting or warming your product, this should be done very carefully in a water bath, with a maximum water temperature of 37 degrees C (check it with a thermometer!).
It is safer to transfuse cold blood and warm the patient, than excessively warm the blood, damage the cells, and increase the risk of a transfusion reaction - so often, letting it come up to room temperature is enough!
(Ideally sterile) gloves should be worn when handling and preparing the product. With canine blood, the bag should be attached directly to, and run through a giving set containing approximately a 172-micron filter, to remove any small clots within the product.
Feline blood should be collected in (or moved into if a bag has been used) multiple 10-20ml syringes. This way, the syringes can be stored in the fridge until they’re needed, maximising their usable life and minimising contamination.
If transferring the product into syringes, ideally use a bag spike rather than a needle, as they are much wider-bore, or if that isn’t possible, use the largest size needle you have, to minimise haemolysis.
When drawing up the product, avoid placing more than 1ml of negative pressure on the syringe at all times, to prevent RBC damage.
The syringes are then attached to an extension set with an in-line 18-micron blood filter, to remove any clots.
Administering the blood
If you can, a new IV catheter should be placed ahead of the transfusion and this only flushed with 0.9% Saline.
We need to make sure that calcium-containing medications or fluids (e.g. Hartmann’s solution) are not given during the transfusion or in the same line as blood. This is important because calcium can interact with the anticoagulant within the blood, causing calcium clumps to form.
Any medications (except for time-critical medications such as analgesia) should also be stopped during the transfusion, and if medications must be given, these should be given through a separate IV catheter.
Patients should also not be fed during a blood transfusion if possible. By avoiding food and medications, we minimise the opportunities for adverse effects to occur which could look like a transfusion reaction.
For example, if a recently-fed patient vomits, how do we know if it’s due to the food or the blood?
Aseptic technique is also an important consideration during the transfusion. We need to avoid disconnecting the blood administration line from the IV catheter where possible. This is because each disconnection and reconnection provides an opportunity for bacterial contamination.
Gloves should also be worn when handling the blood product, patient, or IV catheter.
How do we pick transfusion rates?
Blood is administered initially at a lower rate (0.25-0.5ml/kg/hour) for the first 30 minutes, whilst the patient is monitored for any signs of transfusion reaction.
If there are no issues during the first 30 minutes, the rate can be increased to a slightly higher rate (approx 1ml/kg/hr) for a further 30 minutes.
Again, if all of this is ok, we’ll then increase the rate again. This time, to deliver the entire transfusion over an appropriate period (e.g. a further 3-5 hours, taking your total transfusion time to 4-6 hours).
For example, a 4kg cat (with no history of cardiac or renal disease) needs 30ml of packed red blood cells over an appropriate period.
First 30 minutes: 0.5ml/kg/hour = 2ml/hour for 30 minutes.
After 30 minutes: increase to 1ml/kg/hour for a further 30 minutes = 4ml/hour for 30 minutes.
After this: increase the fluid rate to deliver the remaining blood within a total transfusion time of four hours.
3ml has been given over the first hour (2ml/hr for 30 minutes = 1ml, + 4ml/hr for 30 minutes = total of 3ml).
30ml – 3ml = 27ml.
27ml/3 hours = 9ml/hr.
9ml/hr divided by the patient’s bodyweight is 2.25ml/kg/hour. At this rate, volume overload is unlikely to be a concern, so a 4-hour transfusion time should be ok for this patient.
Monitoring the patient
During any blood product transfusion, we need to keep a close eye on:
Temperature
Heart rate
Pulse quality
Respiratory rate
Respiratory effort/pattern
Arterial blood pressure
Mucous membrane and capillary refill time
Patient demeanour/mentation
Any vomiting should also be noted, and if any urine is passed or blood samples are collected, the urine/plasma colour should also be noted. This is useful since haemoglobinuria and haemoglobinaemia can be seen during transfusion reactions.
How often do we check these?
These parameters should be assessed:
Before the transfusion starts,
Every 5-10 minutes for the first half-hour,
Every 15-60 minutes until the transfusion is complete.
I usually decrease my monitoring frequency to every 15 minutes for a half-hour period just after the blood rate is increased, and then after that, if there are still no signs of transfusion reaction, reduce the frequency of my monitoring to every 30-60 minutes.
Any patient receiving a transfusion should have a nurse always available inside their ward throughout their transfusion so that any deterioration can be identified and managed quickly.
But by reducing the frequency of TPRs as the transfusion progresses, you’re minimising the number of invasive assessments you’re performing on your patient, in turn reducing stress.
Transfusion reactions
So we’re monitoring our patients for any signs of a reaction, but what are we looking out for?
This depends on the type of reaction we see. Reactions can be split into immunological (caused by the immune system) and non-immunological, reactions, as well as haemolytic (where RBCs are destroyed) and non-haemolytic reactions.
Haemolytic reactions
These are caused by antibodies against red blood cell antigens, for example, a type B cat given type A blood.
This causes rapid destruction of the donor’s red blood cells and when this happens acutely, is an emergency as the reaction can be fatal.
Haemolytic reactions can be acute (within the first 15 minutes of the transfusion) or delayed (up to 21 days after the transfusion).
Clinical signs of an acute haemolytic reaction include:
Pyrexia
Tachycardia
Dyspnoea
Hypotension
Seizures
Cardiac arrhythmias
Hypotension
Potentially cardiac arrest
Non-haemolytic reactions
These are antibody-associated reactions to proteins, platelets and white blood cells within plasma products.
These reactions can be seen during the transfusion or shortly afterwards, and clinical signs are similar to allergic/anaphylactic reactions. Pyrexia, hives, itching, redness, vomiting and oedema are commonly seen.
Non-immunological reactions
Non-immunological reactions are varied and have lots of underlying causes. They include:
Microbial contamination of the blood product
Infectious disease transmission from donor to recipient
Pre-transfusion haemolysis (caused by overheating or improper handling/preparation of the blood product)
Another important non-immunological reaction is citrate toxicity. This occurs when there is too much anticoagulant for the volume of blood collected from the donor. The citrate in the anticoagulant binds to calcium in the body, causing hypocalcaemia and cardiac arrhythmias.
How do we manage a reaction?
If signs of a transfusion reaction are seen (or if you suspect them), the transfusion should be immediately stopped and the veterinary surgeon informed.
We normally treat them with intravenous fluid therapy, steroids +/- antihistamines and/or adrenaline. We should be especially thorough with our monitoring in the first 15 minutes of any transfusion because that is when most of the acute/severe reactions occur.
So as you can see, there is so much more we can do to support our transfusion patients - you don’t need to be a vet to calculate, prepare and administer blood, or spot the signs of a reaction!
These patients are fantastic to nurse and they really allow us to use our nursing skills. Do you monitor/give transfusions in practice? Or would you like to brush up on your skills because you don’t do them often? Don’t forget to grab your seat at the haematology workshop here - then DM me on Instagram once you’ve signed up and let me know - I can’t wait to work with you there!
References
Day, M. and Kohn, B. 2012. BSAVA Manual of Canine and Feline Haematology and Transfusion Medicine. Gloucester: BSAVA.
King, L. and Boag, A. 2014. BSAVA Manual of Canine and Feline Emergency and Critical Care. Gloucester: BSAVA.
Merrill, L. 2012. Small Animal Internal Medicine for Veterinary Technicians and Nurses. Iowa: Wiley-Blackwell.