Who does the blood transfusions in your practice? The vets? Or the nurses?

Yes, it will 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 episode of the Medical Nursing Podcast is to take the confusion out of transfusions…  so you can confidently care for your haematology patients in practice.

So, your patient needs blood. What will you give them?

Several blood products are available, and each has its indications and contraindications. As nurses and technicians, it’s vital that we understand these so we can help select an appropriate product and monitor these patients appropriately.

When transfusing a patient, we ideally want to replace only what is lost to minimise transfusion reactions.

For example, let’s 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 necessary components makes each unit of donated blood go further and avoids giving additional unnecessary blood components. 

So what can we give? Well, this depends a little bit on where you are in the world, but in the UK, the products commonly available for our patients are:

• Fresh whole blood

• Stored whole blood

• Packed red blood cells

• Frozen plasma

• Fresh frozen plasma

• Cryoprecipitate

• Platelet concentrate

Let’s look at each of them now, starting with fresh whole blood.

This is blood transfused within 4-6 hours of being collected from the donor. It contains all blood components: RBCs, WBCs, platelets, clotting factors, and plasma proteins.

Platelets are considered non-viable after 4 hours, so if you’re giving whole blood to a thrombocytopenic patient, you ideally want it to be fresh. However, platelet concentrate is also available as a source of platelets (but no red blood cells) in dogs.

Then we’ve got stored whole blood…

This is whole blood that is no longer fresh. It contains all the blood components 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.

And one of our most commonly-used products, packed red blood cells.

Packed RBCs are red blood cells suspended in a very small amount of plasma, anticoagulant and a nutrient mix called SAG-M.

Packed cells are used to correct anaemias that are not associated with haemorrhage or haemorrhage-associated losses if whole blood is unavailable.

They can be stored refrigerated for up to 42 days from collection, though ideally, they should be used within 28 days. The longer red blood cells are stored, the higher the risk of changes affecting their viability—and therefore the higher the risk of complications.

And then we’ve got our plasma products.

Plasma is the liquid portion of the blood after the RBCs are removed. It contains proteins, clotting factors, albumin, and immunoglobulin. 

Several plasma products are available in practice—fresh frozen plasma, frozen plasma, and cryoprecipitate are the three most commonly used.

Fresh-frozen plasma is plasma that has been separated from the red cells and frozen within 8 hours of being collected from the donor. It reliably contains the labile clotting factors (factor VIII, von Willebrand’s factor, and fibrinogen) and can be used for haemophilia patients and those with von Willebrand’s disease—as we chatted about in episodes 43 and 44. 

When stored appropriately, fresh frozen plasma has a year-long shelf life. After one year, the labile clotting factors are no longer considered present, and the product becomes frozen (or stored) plasma. 

Stored or frozen plasma can be used for a further four years and is used to treat coagulopathies not involving those labile factors (e.g. anticoagulant rodenticide toxicity, as we mentioned in episode 45, or hepatic failure-associated coagulopathies), and as a source of immunoglobulin in diseases such as pancreatitis and canine parvovirus.

Lastly, we have cryoprecipitate. This is a plasma fraction made from centrifuging and concentrating fresh frozen plasma. It contains higher levels of those labile clotting factors, so is commonly used for patients with haemophilia or von Willebrand’s disease. 

What about cats?

There is currently no UK feline blood bank for cats, so in most cases, we rely on fresh whole blood transfusions or xenotransfusion, where we administer canine blood products.

Ok, so we know what blood product we need. How do we know what type to give?

Once you know which product your patient needs, you’ll need to blood type them. Blood typing identifies different antigens present on the surface of red blood cells. 

When transfused into a patient with antibodies against a particular red cell antigen, these antigens can cause an acute transfusion reaction. 

Canine blood groups

At least 12 known red blood cell antigens exist in dogs, 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. 

Unlike DEA 1-positive dogs, DEA 1-negative dogs do not have the DEA 1 antigen on the surface of their red blood cells.

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. This 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 DEA 1 negative blood use, 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 currently of unknown significance. Cats are either Mik-positive or Mik-negative; 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 can 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 practice, so the only way to minimise a Mik-associated transfusion reaction is to cross-match the donor and recipient prior to transfusion.

What’s a crossmatch? How does it 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 whether two individuals’ blood cells/plasma are compatible when mixed.

It is one of the most important procedures to reduce the likelihood of a transfusion reaction. There are two types of crossmatch: a major crossmatch and a minor crossmatch.

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. 

So you’ve typed your patient and got your blood… now let’s prep!

The first thing we need to do is determine how much blood our patient needs. Depending on the individual patient and their PCV, we usually give around 12-20ml/kg for whole blood (max 20ml/kg) and 6-10ml/kg for packed RBCs.

As a general estimate, 2ml/kg of whole blood or 1ml/kg of packed RBCs should increase your patient’s PCV by 1%, though there is some variation between individuals.

Once you’ve calculated how much blood your patient needs, you’ll need to plan your transfusion rates.

When giving a transfusion, we ideally want to give the whole thing over about 4 hours. This is because the risk of bacterial contamination increases the longer a blood product is broached—because it contains 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 more extended period (ideally not over 6 hours, if possible, due to the risk of contamination).

We’ll begin at a lower rate (0.25-0.5ml/kg/hour) for the first 30 minutes while monitoring the patient for any signs of transfusion reaction. 

If there are no issues during the first 30 minutes, the rate can be increased to deliver the entire transfusion over an appropriate period (e.g. a further 3.5-5.5 hours, taking your total transfusion time to 4-6 hours).

And then it’s time to prepare!

When preparing blood for transfusion, two main things to consider are aseptic technique and careful handling.

If you’re defrosting or warming your product, do it very carefully in a water bath with a maximum water temperature of 37 degrees C (check it with a thermometer!). 

It is far 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 a 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.

The syringes are then attached to an extension set with an in-line 18-micron blood filter to remove clots.

Administering the blood

If possible, a new IV catheter should be placed ahead of the transfusion, and this should be flushed with only 0.9% Saline. 

We need to ensure 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 essential medications must be given, these should be given through a separate IV catheter. 

Patients should also avoid eating 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 essential consideration during the transfusion. We must avoid disconnecting the blood administration line from the IV catheter where possible 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.

So you’ve prepared your blood product. How will you monitor your patient?

Before your transfusion starts, grab a baseline assessment, including 

• 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.

Once you start your transfusion, you must reassess these parameters regularly. I usually start by assessing them every 5-10 minutes for the first half an hour and then decreasing them to every 30-60 minutes as the transfusion continues.

Try and keep as much of your monitoring as hands-off as possible, using things like a multiparameter monitor to continually monitor non-invasive BP and ECG (and even temperature, if you have a temperature probe) remotely.

Any transfusion patient should also have a nurse always available inside their ward throughout their transfusion to identify and manage any deterioration quickly. 

The risk of a transfusion reaction is highest in the first 30 minutes, so pay especially close attention for that first half an hour.

Speaking of transfusion reactions…

So we monitor our patients for any signs of a reaction, but what should we look out for? 

This depends on the type of reaction we see. There are a lot of different reactions possible, which can be categorised as immunological (caused by the immune system) and non-immunological reactions, as well as haemolytic (where RBCs are destroyed) and non-haemolytic reactions. 

Haemolytic reactions

Haemolytic reactions can either be immunological in origin or due to other factors. 

Immunological haemolytic reactions are caused by antibodies against the patient’s blood type, for example, if a type B cat is given type A blood. 

This can cause rapid destruction of the donor’s red blood cells, and when this happens acutely, it 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

Non-immunological haemolytic reactions occur due to things like infectious disease transmission via the donated blood or pretransfusion haemolysis - where the blood product itself is old or has been excessively warmed and the RBCs have become damaged.

Non-haemolytic reactions

Again, non-haemolytic reactions can be either immunological or non-immunological.

Immunological reactions are are usually 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.

Other causes of non-haemolytic reactions include:

• Microbial contamination of the blood product

• Citrate toxicity (which 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)

• Transfusion-related acute lung injury

• Transfusion-associated circulatory overload

• And lots more!

So, 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. 

From here, how we manage each reaction depends on the type of transfusion reaction our patient has.

The Association of Veterinary Haematology and Transfusion Medicine (AVHTM) has published a fantastic set of clinical guidelines for managing transfusion reactions, which I’d highly recommend you read and follow. These guidelines contain algorithms for treating and managing every type of transfusion reaction, making it really easy to care for these patients!

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!

Do you monitor/give transfusions in practice? Or would you like to brush up on your skills because you don’t do them often? Drop me a message on Instagram, and let’s chat—I love hearing from you! These patients are fantastic to nurse, and they really allow us to use our nursing skills, so if you’ve not gotten that involved with transfusions until now, make sure you do with your next one!

Did you enjoy this episode? If so, I’d love to hear what you think. Take a screenshot and tag me on Instagram (@vetinternalmedicinenursing) so I can give you a shout-out and share it with a colleague who’d find it helpful!

Thanks for learning with me this week, and I’ll see you next time!

References and Further Reading

• 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.

• Odunayo, A. et al. 2021. Association of Veterinary Hematology and Transfusion Medicine (AVHTM) transfusion reaction small animal consensus statement (TRACS). Part 3: Diagnosis and treatment. Journal of Veterinary Emergency and Critical Care, 32 (2), pp. 189-203. Available from: https://onlinelibrary.wiley.com/doi/10.1111/vec.13043

• Obrador, R. et al. 2015. Red blood cell storage lesion. Journal of Veterinary Emergency and Critical Care, 25 (2), pp. 187-199. Available from: https://onlinelibrary.wiley.com/doi/10.1111/vec.12252