Pathogenesis
Volume overload is uncommon in adult horses receiving blood transfusions, but may occur with smaller patients such as miniature horses and foals [16]. Massive transfusion, defined as transfusion of one blood volume or more within 24 hours or 50% of one blood volume within 3 hours, may lead to additional complications [17]. Massive transfusion can cause hypocalcemia associated with citrate toxicity. Liver failure has been reported in neonatal foals receiving large volume transfusions to treat neonatal isoerythrolysis, likely due to iron overload [18].
Prevention
Volume overload can be avoided with careful calculation of total fluid volume planned for treatment of the patient. In normovolemic patients, packed RBCs should be used, when available.
Diagnosis
Clinical signs include dyspnea and cyanosis. Signs of pulmonary edema may be seen on thoracic ultrasound or radiographs.
Treatment
Discontinue the transfusion (if still in progress) and administer supplemental oxygen. Furosemide (1.1 mg/kg IV) should be administered as a diuretic.
Expected outcome
Prognosis is good if the condition is recognized early and treated appropriately, assuming there are not underlying clinical conditions such as heart failure, renal failure, or sepsis.
Transfusion‐Transmitted Infections
Definition
Transfused blood may transmit infection due to unrecognized donor infection or due to bacterial overgrowth in the blood product.
Risk factors
Improper collection and storage of blood, including skin contamination during collection, refrigeration without strict temperature control, break in sterility during warming or administration of blood
Blood‐borne disease in donor horse
Pathogenesis
Bacterial contamination can occur at many points during the collection, storage, and administration of blood products. Horses are most often transfused with fresh whole blood, so the risk of substantial bacterial contamination is low since the blood is not stored. Donor horses may transmit viral, bacterial, and protozoal diseases, such as equine infectious anemia (EIA), piroplasmosis, and equine parvovirus.
Prevention
The USDA issues standards for equine plasma labelled for treatment of failure of passive transfer of immunity and treatment of specific diseases. These standards include testing plasma donors for EIA, piroplasmosis, dourine, glanders, and brucellosis. The USDA recommends additional testing for equine viral arteritis, West Nile virus, and equine parvovirus. The USDA does not have regulatory oversight of whole blood or packed RBCs, but the guidelines for plasma donors are logical for blood donors as well. Blood donors should not give blood if they are showing any signs of illness, including fever.
The blood collection site (usually jugular vein) should be clipped and prepared with a surgical scrub, especially if blood will be stored. Sterile technique should be used with needle or catheter placement and a closed collection system should be used to limit potential for bacterial contamination. Stored blood should not be used if there are any signs of contamination or disruption of the bag. Do not leave blood products at room temperature for more than 4–6 hours.
Diagnosis
Bacterial contamination and production of toxins may result in immediate clinical signs of systemic inflammatory response syndrome in the transfused patient. Fever, tachypnea, and tachycardia can occur for a variety of reasons during transfusion, and regardless of the suspected cause, the transfusion should be stopped. Unfortunately, transmission of viral or protozoal disease will not be immediately apparent, so prevention through donor testing is strongly recommended.
Treatment
The transfusion should be stopped if there are any signs of reaction or suspicion of contamination. Any remaining donor blood can be cultured if bacterial contamination is suspected.
Expected outcome
Outcome will depend on the underlying infection. In humans, approximately 10% of transfusion‐related deaths were due to transfusion‐transmitted infections [19].
RBC Storage Lesion
Definition
The storage lesion refers to red blood cell and biochemical changes that occur during blood storage. These include hemolysis, decreased red blood cell deformability, increased 2,3‐diphosphoglycerate (DPG) levels, increased potassium and lactate, and decreased glucose.
Risk factors
Long duration of storage. The RBCs continue to break down throughout the storage period.
Improper collection or storage. Collection into glass bottles inactivates platelets and increases hemolysis. Improper storage solution will not support RBC metabolism and will lead to more rapid RBC breakdown.
Pathogenesis
The morphologic and biochemical changes in stored blood occur, even in storage solutions that provide dextrose and balance pH. Ongoing RBC metabolism and breakdown lead to an increase in potassium and lactate and a decrease in 2,3‐DPG [20]. As the cell membrane deteriorates, increased hemolysis can be detected and hemoglobin microparticles are released. Large‐volume transfusion of stored blood can introduce high levels of potassium and lactate.
As storage time increases, post‐transfusion viability of the RBCs decreases. The post‐transfusion lifespan of equine autologous RBCs stored for 28 days was 59 days, compared to a lifespan of 99 days for fresh, biotinylated blood [21].
Prevention
Fresh whole blood is most often used for equine transfusions, so “storage lesion” (hyperkalemia, hyperlactatemia, decreased 2,3‐DPG) is not usually a concern. When collecting blood intended for storage, use CPDA‐1 storage bags to support RBC viability. Use a dedicated blood bank refrigerator at 4°C.
Diagnosis and monitoring
Stored blood should be discarded if hemolysis is evident, and storage of equine blood beyond 28 days is not recommended. Horses receiving stored blood should be monitored for hemolysis, hyperkalemia, and poor tissue oxygenation, along with other transfusion reactions.
Treatment
There is no specific treatment indicated for animals that receive older units of RBCs. The decrease in 2,3‐DPG is reversible, so the limitations of oxygen delivery should not be long‐lasting. Additional blood transfusion may be needed if RBC viability has been severely compromised by storage.
Expected outcome
The biochemical and functional changes that occur during RBC storage are similar across species. In dogs, age of the stored RBCs is associated with the risk of transfusion‐related hemolysis, but not with fever or mortality [3].
References
1 1 Hurcombe. S.D., Mudge. M.C., and Hinchcliff, K.W. (2007).