Administering and Monitoring Blood Transfusions

Administering and monitoring blood transfusions, by Kate Tinney Cert IV VN, Dip VN (ECC), Cert IV TAA, AVN, RVN, VTS (ECC)

Canine Blood Types

Canines are blood typed according to the dog erythrocyte antigen or DEA system. There are currently 7 DEA types, they include DEA 1, DEA 3, DEA 4, DEA 5, DEA 6, DEA 7 and DEA 8. These antigens if not matched correctly between donor and recipient can cause immunological reactions.

The term universal donor is commonly associated with donor dog blood types, this means that their blood can be transfused into any canine recipient without causing immunologic reactions as they are negative for each of the RBC antigens. While this is technically virtually impossible as almost all canines are DEA 4 positive, and currently DEA 6 and DEA 8 are unable to be tested. In an ideal world, the closest that we can get to universal is DEA 1 neg, DEA 3 neg, DEA 5 neg, DEA 7 neg and DEA 4 positive. There are commercial blood typing kits that are easy to use in house to test for DEA 1 antigen and this is the most common antigen test used when selecting donors. The other RBC antigens that can be tested at selected external laboratories include DEA 3, DEA 4, DEA 5 and DEA 7. Because most of the antigens are not readily testable it is common practice to have a DEA 1 neg donor and perform a crossmatch prior to transfusion to identify any other antigen mismatches. In house DEA 1 testing is quick, easy and affordable and should be performed with all potential donors, with DEA 1 negative being the most ideal donor.

Feline Blood Types

The most widely accepted blood group for cats is the AB blood group system, it comprises three blood types, type A, type B and type AB. Type A is often most common, but some purebred breeds have a higher representation of type B cats while type AB is rare. Blood typing in cats is critically important, shortly after kittens are weaned, they can naturally develop alloantibodies to the opposite blood type to themselves even without prior sensitisation. These alloantibodies have the potential to cause fatal transfusion reactions and is the reason that every donor and recipient cat MUST be typed prior to transfusion. Type B cats have the strongest of these alloantibodies and as a result, even if they receive only a small volume of type A blood it can cause a fatal reaction. Type AB cats are the exception and do not have alloantibodies to either A or B blood, their ideal donor match would also be AB, however, they are uncommon and as such not commonly in donor programs. If an AB recipient requires blood and there is no AB donor available, the next best donor type is A, this is because type B cats have the strongest alloantibodies, however, it is important to understand that transfusion reactions are still possible. There are commercially available feline blood typing kits that can be used for in house typing, they are quick, easy and inexpensive to use.

Crossmatching

Crossmatching for both dogs and cats should still be performed even on first transfusions with matching blood types. Although it is often not commonly performed in clinic for first transfusions, it is important that if any subsequent transfusions are required, especially if several days have passed since the initial transfusion a crossmatch is performed to identify any incompatibility. This is due to the recipient developing antibodies several days following the first transfusion. Both canine and feline cross matching kits are commercially available for in house use. Crossmatching kits take approx. 20minutes to complete and although they have many steps to follow thorough instructions are provided.

Monitoring

It is important that any patient receiving any blood product is monitored closely to observe for potential transfusion reactions. Although most severe reactions will happen early in the transfusion, reactions can happen at any time during the transfusion and even hours to days after. If at any point you suspect a transfusion reaction the most important thing is to STOP the transfusion and notify the Veterinarian in charge of the patient and they will direct you to what additional steps will need to be taken to manage the reaction. If the Veterinarian directs you to administer other fluids or medications, the administration line, extension set and t-piece should be changed to minimise flushing further blood product into the recipient, this is especially important in the event of a severe reaction.

It is important when monitoring a transfusion that you take baseline vital signs prior to the transfusion starting, this helps to be able to identify any early changes which may indicate a reaction. Monitoring should include

• Demeanour
• Heart rate
• Respiratory rate and effort
• Temperature
• Mucous membrane colour and Capillary refill time
• Pulse Quality
• Blood pressure
• Oxygen saturation

Once the transfusion starts usually initially at a slow rate and gradually increasing. It is important to continuously monitor the patient and record vital signs every 5 mins for the first 20 minutes. If there is no evidence of a reaction after 20 minutes vital sign recording can be reduced to between 15-30 minutes depending on clinic protocol and patient tolerance. It is also important to record the donors name and PCV/TP for whole blood transfusions, or for component therapy products the batch number and expiry date. If your clinic does not have transfusion monitoring charts examples can be downloaded from the internet. In the ideal situation the patient would not receive any other medications or food during the transfusion as if these cause complications such as vomiting or blood pressure fluctuations which may be mistaken for a transfusion reaction. There is also a risk that the medications if administered intravenously can interact with the blood product. 0.9% NaCl should be the only fluid given concurrently if fluid therapy is indicated. Care must be taken to monitor for signs of circulatory overload. All administration lines, catheters etc should be flush with 0.9% NaCl before and after the transfusion.

It is important to remember that monitoring does not stop at the end of the transfusion, in addition to a final vital sign check at the end, the patient should have a PCV 1-2 hours, 12 hours and 24 hours post transfusion, this provides valuable information on PCV, total protein levels and serum colour. Serum colour change can indicate haemolysis has/is occurring, this can be extravascular (bilrubinemia) which is indicated by icterus or intravascular (hemoglobinemia) which is indicated by haemolysed serum. It is a good idea to keep a haematocrit tube from each sample so that the colour can be compared to previous samples.

Completed transfusion monitoring charts should be filed according to clinic protocol.

Transfusion Reactions

Clinical signs that can indicate a transfusion reaction can include one or more of the following: vomiting, fever, urticaria, oedema, hypotension, tachycardia or bradycardia, arrhythmias, abnormal mucous membrane colour, abnormal capillary refill time, tachypnoea or dyspnoea. Many of these signs can indicate either immunologic or non-immunologic. The most important thing to do if you suspect a transfusion reaction is to STOP the transfusion and notify the Veterinarian IMMEDIATELY. Treatment is usually supportive in nature. Transfusion reactions can range from mild to life-threatening and can be broken up into two main categories

• Immunologic reaction
• Immunological reactions are related to the recipient’s immune system. Examples include
  • Febrile non-haemolytic – these are the most common. Most likely from residual WBC in the blood product, which can increase cytokine production and therefore the associated inflammatory response.
  • Acute or delayed haemolytic – occurs when recipient antibodies react with donor RBC surface antigens. This leads to damage to the RBC membrane and intravascular haemolysis occurs.
  • Allergic – can range from urticaria to severe anaphylactic shock. In cats, this commonly manifests at tachypnoea/dyspnoea as the lungs are the shock organ. In dogs, they are most likely to have a hypotensive collapse and can often develop haemorrhagic gastroenteritis as the gastrointestinal tract is the shock organ.
• Non-immunologic reaction
• Non-immunologic reactions are not related to the recipient immune system. Examples include
  • Sepsis – from a blood product with bacterial contamination
  • Disease transmission – from inappropriately screened donors
  • Citrate toxicity – More common when patients receive large volumes of blood and therefore more anticoagulant causing hypocalcaemia
  • Circulatory overload – signs can include tachypnoea, pulmonary oedema

Preparation and Administration of transfusion

Refrigerated products such as stored whole blood and packed red blood cells can be given straight from the fridge. The initial slow rate of infusion allows the blood to reach room temperature as it travels through the administration set. For patients that are already hypothermic or smaller patients who at risk of becoming hypothermic the blood can be warmed to room temperature using a water bath at 37°C prior to infusion. To minimise the risk of bacterial contamination it must be warmed immediately before the transfusion begins as the blood should only be out of the fridge for a maximum of 4 hours (including transfusion time).

Frozen products such as FFP and FP need to be thawed prior to administration. To prevent contamination in the event of damage to the bag they should be placed in a double zip lock bag. To safely thaw the product they should be placed in a water bath that is at 37°C.

All blood products should be administered intravenously, however if venous access is unavailable, intraosseous can be used. Fluids that contain calcium or glucose should be avoided to prevent erythrocyte lysis or coagulation. 0.9% sodium chloride is safe to concurrently administer with blood products and all lines and catheters should be flushed with saline prior to commencing the blood transfusion and again at the conclusion of the transfusion. If patients are receiving saline infusion during transfusion they must be carefully monitored for signs of circulatory overload.

All blood products must be administered using a filter to remove clots and larger platelet aggregates. Canine blood products should be administered using a gravity flow through filtered administration set. These admin sets have filters ranging from 170-260µm depending on the brand. Canine blood products should not be administered through a in line micro-aggregate filter, as the filter in these is much smaller and causes shearing injuries to the canine erythrocytes, which dramatically reduces their life span, some studies suggest to less than 24hours. Gravity fed is the best method of delivery to preserve the red blood cells. The disadvantage of gravity fed is that it can be hard to accurately dose especially early in the transfusion when rates are slow. Specific blood infusion pumps are available, however they are expensive especially if not frequently used. It is common in clinic to administer blood through a volumetric pump, however this still carries some risk to the canine erythrocytes and may reduce their life span. Plasma products can be safely delivered through a volumetric pump. Feline products can be safely delivered through an in-line micro-aggregate filter and syringe driver. Feline erythrocytes are much smaller and can pass through the smaller filter without damage.

While the rate that the transfusion is administered will be determined by your Veterinarian, the severity of the case and patient tolerance. Common protocol is to start at 1ml/kg/hr for 10 mins, if there are no signs to indicate a reaction then the rate can be increase to 2ml/kg/hr for another 10mins, then 4mls/kg/hr. If there remains no reaction signs then most patients will be able to increased to a maximum of 10ml/kg/hr, although patients with higher risk of circulatory overload may have a maximum transfusion rate of 5mls/kg/hr. Patients with critical blood loss may require faster administration and in some cases it is required to be administered as fast as possible. If the patient is tolerating the transfusion it should be completed over a maximum of 4 hours, due to the increased risk of bacterial contamination when blood is at room temperature for greater than 4 hours.

Xenotransfusion

Xenotransfusion is the transfusion of blood from a different species of animal. While it is always ideal to have the most compatible donor, in situations where a compatible donor is not available and the recipient critically requires blood, a xenotransfusion could be considered. There are several studies where dog blood has been successfully transfused into cats. The process however is not without risks and must only performed once. While severe acute reactions are not commonly observed with first transfusion, the feline recipient will develop antibodies against the canine erythrocytes within several days. This antibody development means that subsequent canine transfusions result in fatal anaphylactic reactions in >66% of cats (Clark and Kiesel 1963; Bovens and Gruffydd-Jones 2013). The average life span of xenotransfused erythrocytes is short, on average lasting 3-4 days, while this is not long, it may allow time for a more suitable donor to become available. If a xenotransfusion is to be administer the Veterinarian must discuss the risks with the owner, it is also important that this owner notify future treating Veterinarians to prevent the recipient from receiving a dog blood product again.

Massive Transfusion

Massive transfusion is when a patient receives their total blood volume, dogs >90ml/kg and cats 66ml/kg or more in transfusion products in a 24hour period or half their blood volume in 3-4 hours. This extensive transfusion volume places the patient at higher risk of complications in addition to their underlying critical status.

In addition to the previously mentioned risks, massive transfusion administration holds additional risks such as:

• Electrolyte imbalances
  • Hypocalcaemia and Hypomagnesemia – caused by the anticoagulant citrate that rapidly binds to calcium and magnesium. Often electrolyte imbalances are short lived as the citrate is metabolised by the patient’s liver (providing they are not suffering from hepatic disease). In severe cases calcium and/or magnesium may need to be supplemented.
  • Hyperkalaemia – increased potassium can be from multiple causes, including potassium moving from intracellular to extracellular space secondary to acidosis and volume depletion and decreased potassium excretion from decreased urine production. In severe cases this can lead to life threatening arrythmias.
• Haemostatic defects
  • Patients often develop thrombocytopenia as they have used up their own platelet stores and stored blood has no viable platelets.
  • Platelets can become dysfunctional secondary to acidosis or hypothermia.
  • Secondary coagulopathy – they have used up all their clotting factors and depending on what transfusion products they are receiving coagulation factors may or may not be present.
  • The combination of hypothermia and shock plus cold blood products can affect function of coagulation factors leading to a secondary coagulopathy.
• Stored red blood cells use glucose, this metabolism increases lactic and pyruvic acids which in large volumes can increase the severity of metabolic acidosis.