Identifying the Need For Blood Transfusions and What Products We Have

Identifying the Need For Blood Transfusions and What Products We Have, by Kate Tinney Cert IV VN, Dip VN (ECC), Cert IV TAA, AVN, RVN, VTS (ECC)

Why do patients require blood transfusions?

The most important role of blood is the erythrocytes oxygen-carrying capacity and delivery to the tissues. When a patient becomes severely anaemic or loses >20% of their blood volume through a haemorrhage their ability to deliver oxygen to the tissues can be compromised. Without intervention, this can lead to tissue hypoxia and death. It is important to remember that while administering crystalloids can help restore blood volume it does not increase the number of erythrocytes or haemoglobin therefore it may not improve the patient’s oxygen-carrying capacity. This is the reason why anaemia is the most common reason that a patient will require a blood transfusion. Patients suffering from coagulopathy is the other common reason for administering a blood transfusion or blood product.

Common causes of reduced blood volume or components

• Inadequate blood volume or components can be caused by one or more reasons
• Loss eg usually acute haemorrhage, causes include trauma, ruptured vascular tumour, lacerated major blood vessel or artery, surgery, parasites, coagulopathies
• Inadequate production eg bone marrow suppression, renal failure, hepatopathy or an inability to be replenished eg rodenticide (Vit K1) toxicity
• Excess destruction or cell alteration eg immune-mediated conditions, such as immune-mediated haemolytic anaemia, immune-mediated thrombocytopenia, heavy metal toxicity, medication such as acetaminophen and parasites such as mycoplasma
• Increased consumption, coagulation factors are used faster than they can be regenerated eg disseminated intravascular coagulopathy or brown snake venom-induced consumptive coagulopathy

Indications for blood products

Before administering a blood transfusion or any blood product, it is important that the type of loss and specific patient requirements are identified. This allows us to administer a transfusion product to fulfil the patient’s requirements to maximise patient outcomes and minimise the risk of complications.

It is important to remember that not all patients will require a transfusion at the same laboratory value. Patients with acute loss will require transfusions with higher laboratory numbers than those with chronic loss. As such it is important that Veterinarians consider the patient's demeanour, circulatory status, oxygenation status, history and differential diagnosis in addition to laboratory values before making the decision to transfuse or not.

An anaemic dog clinical assessment score system (Kisielewicz et al. 2014) was created to provide Veterinarians with an objective measure to guide on the need to administer a transfusion. Each measurement is given a score ranging from 0-3 and totalled. The higher the score the more likely a patient will benefit from a transfusion. The score can be repeated post-transfusion to objectively measure clinical improvement.

Anaemic dog clinical assessment score (ADCAS)

In conjunction with the above clinical signs, laboratory values that can indicate the need for a transfusion include PCV < 20% who are unable to provide adequate oxygen to tissues, or severely extended coagulation times PT >100 seconds and aPTT >300 seconds with evidence of active bleeding.

Component therapy

Because not all patients require all aspects of whole blood and in some cases, the larger volume or specific components of whole blood may be detrimental to the recipient, component therapy is often used to provide the patients specific requirements only. Component therapy is when fresh whole blood is separated very soon after collection into different products. Component therapy has been used in dogs in Australia for many years and is becoming common practice. While it is not yet common in cats in Australia some large specialist hospitals in the last couple of years are separating cat blood into components for in house use. Cat component therapy is quite common in other countries such as the USA. The most common canine component therapies used in Australia are packed red blood cells (PRBC) and fresh frozen plasma (FFP). Other canine products that are commercially available in America include frozen platelet concentrate, platelet-rich plasma and cryoprecipitate.

Benefits of component therapy include the donor being able to help more than one patient for each donation given which maximises resources. The risk of transfusion reactions or complications is reduced by not administering components not required by the recipient and minimising volume which is especially important in recipients susceptible to circulatory overloads such as small patients or those with pre-existing cardiac or renal disease.

The disadvantages of producing in house component therapy are it requires specialised equipment, training and storage requirements. If you don’t have components readily available, then they take time to prepare and this time delay may not be suitable in emergencies.

Currently, only canine component therapy products can be purchased commercially in Australia.

Blood Products Options

Fresh whole blood

Fresh whole blood is when whole blood is collected from the donor and transfused into the recipient within 8 hours of collection. If it is not immediately transfused to the recipient, it must be stored in the fridge (2-5°C) for a maximum of 8 hours. After 8 hours of storage, it is considered stored whole blood.

Stored whole blood

Stored whole blood is whole blood that is collected and stored for later transfusion.

Packed Red Blood Cells

Almost all plasma has been removed, a higher concentration of RBC than whole blood.

Fresh Frozen Plasma

Fresh frozen plasma is separated from red blood cells and frozen.

Cryoprecipitate

Cryoprecipitate is a product that is produced using a residue obtained from thawing FFP, it has large numbers of fibrinogen, fibronectin, factor VIII, factor XIII and von Willebrand’s factor. It can be stored in the freezer for up to 12 months. Cryoprecipitate contains 20 times the vWF per ml than FFP, making it the component of choice for treatment for von Willebrand disease. It is administered at a dose of 1- 2mls/kg every 12 hours as clinically required. It is currently unavailable in Australia.

Storage Considerations

A dedicated blood fridge/freezer is ideal to maximise the life of the blood products. Being separated from other products prevents potential contamination and minimises regular fridge/freezer opening. There should be continuous temperature monitoring with an alarm if the temperature goes outside the specified range. Significant fluctuations in temperature can affect blood cell viability by causing haemolysis and increasing the risk of bacterial growth.

Products that contain red blood cells such as stored whole blood and packed red blood cells should be stored in an appropriate blood fridge at 2-5°C. Stored whole blood can be stored for up to 28 days and PRBC can be stored for up to 35-42 days depending on the anticoagulant preservative used. All stored products containing red blood cells should undergo gentle agitation of the bag daily to evenly distribute the dextrose, adenine and other products to maximise cell viability. The manufacture of CaniRBC recommends their products be hung separately in a vertical position in the fridge. An in vitro study in humans suggested that horizontal storage provided optimal blood gas values. More research may be required to determine if horizontal or vertical is the ideal method.

Frozen products such as FFP and FP need to be stored at ≤ -18°C. Ideally, a non-automatic defrosting freezer is used to avoid temperature fluctuations during regular defrosting. FFP that has been frozen within 8 hours of the collection has a one-year expiry, after which time it is considered FP, FP that has remained frozen has a 5-year expiry. Frozen plasma should be kept in its original cardboard packaging handled carefully as the packaging can be brittle and is susceptible to damage. If FP or FFP has been thawed and isn’t immediately transfused it can be stored in a blood fridge for up to 5 days, viable coagulation factors would be considered the same as FP.

Ideal donor qualities

Correct donor selection is critical for both the health and well being of both the donor and the recipient. Donors should have a calm temperament and be happy to be in the hospital environment. A minimum of 6 weeks between donations is required, however, to maximise the length of the donor remains in the program ideally 10-12 weeks between donations is advised. Selecting the correct donor will improve the success of the program. Ideal qualities include:

• Age between 1 and 7 years
• Ideal body condition with weight for dogs >25kg and cats >5kg
• Not previously received a blood transfusion
• Up to date with vaccinations and parasite prevention (as per geographical location)
• Negative to infectious diseases as per ACVIM minimum guidelines and regional locations
• No history of recent illness and not on any medications
• Normal physical exam and laboratory work
• Dogs PCV >40% with TP 60-85g/L and cats PCV >35% with TP 65-85g/L
• Blood type – dogs ideally DEA 1 neg (preferably also DEA 3, 5 & 7 neg), cats must be same blood type as the recipient
• Cats who will donate on a regular basis should receive an echocardiogram to rule out any underlying cardiac disease, especially Hypertrophic cardiomyopathy (HCM). As some cats with HCM show no clinical signs, and if present it may increase the risks to the donor.

While previously female donors that have had litters were excluded from donating, a study has demonstrated that blood from dogs with previous pregnancies can safely be used for transfusions (Blais et al. 2009)

The American College of Veterinary Internal Medicine (ACVIM) published an update in 2016 that provides guidelines in minimal infectious disease screening. It also provides an example form for prospective donors and a health info sheet for donors to complete at each donation.

When collecting blood from donor animals it is important that meticulous records are kept. Each animal requires their health assessments documented including vaccinations, preventative health, infectious disease status, laboratory work both annual and at the time of donation. Their maximum donation each time is 20ml/kg in dogs, usually a full unit of 450ml +/- 50mls and 10ml/kg in cats.