of the transfusion. Any signs of anaphylactic reaction warrant immediate discontinuation of the transfusion and treatment with epinephrine (0.01–0.02 mg/kg IV).
Expected outcome
FNHTR is usually self‐limiting. There is a risk of recurrence with subsequent transfusions. Mild allergic reactions can usually be treated successfully. Anaphylactic reactions may be fatal.
Transfusion‐Related Acute Lung Injury
Definition
Transfusion‐related acute lung injury (TRALI) is a new onset of bilateral pulmonary infiltrates within 6 hours of transfusion. TRALI follows the criteria for acute lung injury (ALI), defined as acute onset respiratory difficulty with evidence of pulmonary capillary leakage, no evidence of left atrial hypertension, and PaO2/FiO2 of less than 300 mmHg [12]. TRALI is an important cause of transfusion‐related mortality in humans. TRALI has been described in dogs but has not been reported in horses. Nonetheless, it is an important potential adverse reaction to consider and include in the list of differential diagnoses for dyspnea or hypoxemia after transfusion.
Risk Factors
Leukocyte antibodies in the donor may react with leukocyte antigens in the recipient, leading to sequestration and activation of neutrophils in lung tissue.
Activation of cytokines and lipids may also cause damage to the pulmonary vascular endothelium.
Activation of neutrophils related to infection, inflammation, or trauma may be the “first hit” prior to the “second hit” of the transfusion.
Pathogenesis
Activation of neutrophils (see above) leads to damage to the pulmonary capillary endothelium, with subsequent capillary leak. Priming of the neutrophils may occur from an initial event (e.g. trauma, surgery, infection). Activation of the neutrophils in the pulmonary endothelium then occurs secondary to transfusion‐related immune stimulation.
Prevention
Leukocyte antibodies in donor blood can be reduced by processing whole blood into packed RBCs and by washing RBCs.
Diagnosis
Clinical signs of TRALI include hypoxemia, cyanosis, tachypnea, and tachycardia, usually within 6 hours of transfusion. Volume overload, allergic reaction, and systemic inflammatory response syndrome should also be considered as differential diagnoses.
Treatment
Hypoxemic patients should be treated with supplemental oxygen. Conservative fluid therapy is indicated to reduce the risk of volume overload.
Expected outcome
TRALI is usually self‐limiting in humans, with recovery in 48 to 96 hours, although mortality is reported as high as 25% [13]. The incidence of TRALI in dogs appears to be low (3.7%) and not significantly different than the incidence of ALI in critically ill dogs that have not received transfusions [14].
Nonimmune Reactions
Volume Overload
Definition
Volume overload, or transfusion‐associated circulatory overload (TACO), is recognized when signs of respiratory distress and pulmonary edema occur after a large volume transfusion.
Risk factors
Large volume of whole blood given to normovolemic patient
Total dose (ml/kg) of blood products was a risk factor in a study of dogs receiving packed RBC transfusions [15].
Large volume of crystalloid or colloid fluids administered in addition to blood transfusion
Preexisting conditions, such as heart failure and renal failure
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
