The use of feline blood transfusions is commonplace in many veterinary practices. This type of therapy is a lifesaving intervention for feline patients with conditions such as anaemia, coagulopathies and trauma.
Feline blood types
Feline blood types are determined using the AB blood system, which consists of three blood groups: A, B or AB. The clinical significance of feline blood groups is mainly because of the high level of naturally occurring alloantibodies (Giger, 2015).
During transfusion, cats with types A or B should only receive their corresponding blood type. Cats with the much rarer AB blood type should, where possible, receive AB blood: however, due to its rarity, this is not always available. As such, type A blood would be the next best choice (Gibson and Callan, 2018).
According to (Gibson and Callan 2018), cats with type A blood are more common than those with type B. (Gibson and Callan 2018) found that 68% of non-pedigree cats were type A, 30% were type B and 2% were type AB (Table 1). Therefore, it is important to ensure that practices that perform feline blood transfusions aim to have both type A and type B cats on their donor list.
| Type A | Type B | Type C |
|---|---|---|
| Most predominant in domestic catsBreeds with higher prevalence; Main Coons and Siamese | Geographical location can show variation of prevalenceBreeds with higher prevalence; British shorthairs, Turkish Angora/Vans | Rarest blood type |
The importance of blood typing and cross matching
In an emergency and critical care setting, blood product administration will be required promptly. Nevertheless, it is of critical importance that blood typing and cross-matching are completed to promote better patient outcomes. Blood typing is a crucial in the prevention of potentially fatal incompatibility reactions to which feline patients are more susceptible due to the high likelihood of naturally occurring alloantibodies (Pet Blood Bank UK, 2023) (Figure 1). In-house card-agglutination tests such as the Feline Quick Test and the Rapid Vet-H Feline are commonly used to determine blood type in these circumstances (Figure 2).
The (Pet Blood Bank 2023) recommends that all feline transfusions are cross matched to confirm the compatibility of donor and recipient blood and to minimise type mismatched immunological transfusion reactions. For example, the administration of type B blood to type AB recipients (Gibson and Callan, 2018) (Figure 3).
User error and misinterpretation of in-house test results can occur due to promptitude and/or lack of training. These errors may be eradicated with the use of specialist laboratories: however, in-house testing is favourable because of the efficiency of obtaining results, which typically take approximately 5 minutes.
Donor selection, health testing and criteria
It is crucial that donors are healthy and their donation will not be detrimental to their wellbeing. and the blood avoiding spread of infectious diseases among the species
Assessing the suitability of individual feline donors and the safety of their blood products is necessary for protection and safety of both the donor and recipient. Donor selection and health testing of feline donors is necessary to maintain patient safety and avoid the spread of infectious diseases among the species.
The (Pet Blood Bank 2023) lists the criteria for feline donors as follows:
- Fit and healthy individual
- Good temperament
- Over 4 kg
- Up to date with vaccinations, flea and worming treatments
- Between 1–10 years old
- Not on any medication
- Never outside of the UK
- Never had a blood transfusion.
The donor may be an indoor or outdoor individual and will require a full clinical examination by a veterinary surgeon along with sampling for blood-borne pathogens such as feline leukaemia, feline immunodeficiency virus and mycoplasma haemofelis. These tests need to be repeated before each donation if the donor has access to the outdoors. To protect the donor's wellbeing, they must be placid in temperament.
To establish good donor health, several pre-donation blood tests are recommended (Gibson and Callan, 2018; Nectoux, 2022):
- Non-invasive blood pressure
- Echocardiography
- Biochemistry and haematology.
As a result of the current complexities associated with feline blood collection and storage, the authors recommend that larger practices and hospitals keep an up-to-date donor list ready for emergencies. Owners may also register their cats as donors with the Pet Blood Bank.
Feline blood collection
Preparation of the donor cat
Before collection, feline blood donors must have a thorough physical exam by a veterinarian. This should include auscultation of the heart, auscultation of the lung fields, palpation of lymph nodes to check for enlargement and palpation of the abdomen (Giger, 2015). The patient must also be weighed to ensure that no more than 10–12 ml/kg of blood is collected.
Preparing for donation
This article will focus on the open method of blood collection.
Preparation is key when organising the collection of blood. Box 1 and Figure 4 provide the equipment list. This is a guideline given from the author's experience. The authors recommend the use of a topical local anaesthetic cream such as ‘EMLA’ up to 60 minutes before venipuncture.
Box 1. Feline blood collection equipment list
- Intravenous catheter (22-gauge), T-connector, flush, tape and preparation swaps
- Quiet clippers
- Intravenous fluids and giving set
- Fluid administration pump
- Sedation as advised by veterinary surgeon
- Anaesthetic machine with oxygen source
- Endotracheal tubes and laryngoscopes
- Pulse-oximetry and blood pressure
- Patient warming device
- 19–21-gauge butterfly catheter
Blood collection
Most cats will require sedation or general anaesthesia for blood collection (Figure 5). The use of Acepromazine is advised against as it can cause platelet dysfunction, which is undesirable for both donor and recipient (Giger, 2015). Blood is collected by jugular venipuncture with the cat restrained in either lateral or sternal recumbency. Blood collection occurs in the following steps:
- An intravenous catheter is placed and flushed to ensure patency (Figure 6)
- The preferred sedation is administered
- The patient is restrained in the phlebotomist's preferred position
- The fur over the jugular vein is clipped and the area is aseptically prepared
- The butterfly catheter is connected to one of the three 20 ml syringes and primed with anticoagulant
- The vein is accessed by the phlebotomist while another team member slowly collects the blood. The blood should be collected over 10–15 minutes with the syringe being continuously rotated to ensure even mixing of the anticoagulant. See Figure 4 for blood collection equipment.
Blood administration
It is generally the responsibility of the RVN to set up and monitor blood transfusions. The Veterinary Surgeon will direct the rate and amount of blood to be transfused. The volume of blood required is calculated via the following formula: Volume(ml)=60 Bodyweight(kg)[(Target PCV-Current(Recipient)PCV)/Donor PCV]
Ideally, the same nurse should monitor the transfusion from start to finish to ensure any minor changes in the cat's demeanor are recognised. The transfusion should be conducted in a quiet environment. Baseline observations, including heart rate and pulse quality, respiration rate, mucous membrane colour (Figure 8), capillary refill time, blood pressure and temperature should be taken and recorded before starting. Documenting these baseline observations will aid the RVN in identifying any potential complications. The time taken for a patient to develop clinical signs of an immunological transfusion reaction can considerably vary, depending on if the patient has pre-existing antibodies. The severity of the reaction is also dependent on how much blood product they have already received. For this reason, it is recommended by the (Pet Blood Bank 2023) that blood transfusions be administered slowly for the first 20–30 minutes at 0.25-1 ml/kg.
Patients with pre-existing antibodies will experience an acute immunological transfusion reaction. The body will start to haemolyse the transfused blood cells. Some common clinical signs are fever, tachycardia, dyspnoea, muscle tremors, weakness, collapse, vomiting and haemoglobinaemia/uria. It is important to be aware that cats may display bradycardia if they are in shock.
If a patient does not have pre-existing antibodies, then a delayed immunological transfusion reaction may occur. A delayed response is usually identified between day 2 and 21 post-transfusion and the signs are similar to those of an acute immunological reaction, though less intense. The patient may appear jaundiced, anorexic and febrile, and a drop in PCV will be evident (Gibson and Callan, 2018).
Blood transfusions should be administered over 4 hours or less to reduce the risk of bacterial growth. Blood should be handled aseptically at all times and once connected should not be disconnected until the transfusion is finished. If other medications or intravenous fluids are required, these should be administered via another intravenous catheter.
Post-transfusion care
Recipient cat
Transfusion reactions can occur immediately (acute immunological or non-immunological) or may be delayed (delayed immunological or non-immunological). With constant patient monitoring and good knowledge of potential reaction signs, the RVN plays a pivotal role in maintaining patient safety during these critical times.
To assess the effects of the treatment and monitor for complications such as haemolysis and transfusion-related reactions, continual patient checks should be performed regularly during the aftercare. Patient checks should include, temperature, pulse rate/quality, respiration rate/effort, mucous membrane colour and capillary refill time. PCV, total protein and plasma colour should also be included and compared with the pre-transfusion PCV. (Gibson and Callan 2018) suggested that these parameters are monitored immediately after and at the 12- and 24-hour post-transfusion mark.
The patient's IV catheter should be flushed with 0.9% sodium chloride. The IV catheter can then be used to administer any required treatments such as IVFT and IV medications.
In the authors’ experience, the most frequently observed sign of a transfusion-related reaction is the development of pyrexia, this may or may not be accompanied by changes to the respiratory rate/rhythm and/or heart rate/rhythm.
Other clinical signs that may accompany a transfusion reaction are urticaria, oedema, a change in mucous membrane colour and gastrointestinal signs such as vomiting and diarrhoea. In the event of a potential or actual transfusion reaction, the VS must be immediately alerted, and the transfusion should be discontinued.
Both immunological and non-immunological reactions may occur during the recovery period. Thus, the RVN must be able to recognise subtle changes in the patient's condition.
After the administration of large volumes of blood products, complications such as dyspnoea/tachypnoea, tachycardia and cough are associated with circulatory overload as a result of an extremely fast transfusion rate. In severe cases, or those with pre-existing cardiac/renal disease, pleural effusion and pulmonary oedema may develop.
Hypocalcaemia can occur. Hypocalcaemia in the immediate post-transfusion phase is likely caused by citrate intoxication from the anticoagulant used during blood collection. Clinical signs may include hyperaesthesia, muscle tremors, collapse, seizures, vomiting and cardiac arrhythmias (Gibson and Callan, 2018).
Delayed non-immunological transfusion reactions such as sepsis can occur if using incorrectly stored blood products because of bacterial contamination/growth. This can lead to endotoxic shock, disseminated intravascular coagulation and death. Signs are reported to develop 1-2 days post-transfusion and include vomiting, diarrhoea, tachycardia, pyrexia, collapse, hypotension and haemolysis.
Donor cat
The donor should be monitored carefully during the recovery period in a quiet environment. It is recommended by the (Pet Blood Bank 2023) that they are cage rested for 3-4 hours after the donation process and that close monitoring continue during this period. Post-procedure monitoring should include an assessment of the patient's temperature, heart rate, respiration rate/effort, MM colour, CRT and NIBP (Figure 9).
Fluid therapy may be prescribed to the donor by the veterinary surgeon. In the experience of the author, this is usually a crystalloid solution administered at 3 0ml/kg over 3 hours. Monitoring the donor closely post-donation will enable fast identification of any potential complications that may arise, for example, fluid overload and pulmonary oedema.
Once they have recovered and appear alert, they may be offered a small meal and fresh water. Donors may return home once they have recovered from the procedure, have received all prescribed treatments and have eaten. In the authors’ opinion, it is recommended to keep outdoor cats inside for 24 to 48 hours so that their owners can continue to monitor them at home, returning them to the practice if they are concerned.
Conclusion
As highlighted throughout this article, RVNs are indispensable when it comes to nursing when it comes to feline blood transfusions. However, some RVNs may find the idea of feline transfusion medicine daunting. By being advocates for patients, promoting feline-friendly practice and maintaining good knowledge of feline donation requirements, RVNs can promote better patient outcomes. With good knowledge and collaboration, being involved with these cases can be extremely rewarding as they require a lot of nursing input leading to a feeling of fulfilment.
KEY POINTS
- Feline blood transfusions are a vital lifesaving intervention for various conditions.
- Cats have three blood types (A, B, and AB), and compatible transfusions are critical due to naturally occurring antibodies.
- Blood typing and cross-matching are essential to ensure compatibility and prevent fatal reactions.
- Donor selection and health testing are crucial to ensure the safety of both the donor and recipient.
- Careful monitoring during and after the transfusion is essential to detect and manage any potential complication.