Page 94 - WSAVA2017
P. 94

An Urban Experience
absolute PCV a patient will show clinical signs is variable and the need for transfusion determined on a case by case basis. In general, once the PCV falls below 15% a transfusion is administered. It is ideal to confirm blood type of the patient using immunochromatographic methods (Abaxis/DMS) and transfuse with the same type blood. Erroneous results can be obtained with card blood typing methods in extremely anemic animals (PCV < 10%). It is recommended that all cats have a cross match, and dogs having had a previous transfusion have a cross match to identify the potential for a transfusion reaction. However, auto-agglutination will mask a true allogenic reaction and may not be reliably assessed. Fluid administration rates depend on the severity of clinical signs related to the anemia and/or the presence of hypovolemia. In general, the amount of blood administered is enough to increase the PCV to an acceptable level for reestablishing adequate tissue oxygenation without causing fluid overload,
usually around 20-25%, understanding that ongoing destruction may require additional infusion. The amount of reconstituted pPRBC that is needed can be calculated as follows:
2 X Desired PCV(%) X Body Weight (kg)
Definitive treatment of IMHA requires treating any underlying disease processes and suppression of the immune system. The most common immunosuppressive medication used is prednisone (2 mg/kg q 24h, up to 40 mg/dog; 2-4 mg/kg q24h in the cat). Dexamethasone (0.3-0.5 mg/kg IV) can be substituted for prednisone
as an injectable corticosteroid during induction of immunosuppression and if the patient is unable to tolerate oral medication. Common side effects of this drug include increased water intake, urination and increased appetite as well as excessive panting. Occasionally gastrointestinal ulcer formation can occur. If the side effects of prednisone become intolerable or severe gastrointestinal ulceration occurs, alterations in the dose and frequency may be made necessary. Corticosteroids should never be acutely discontinued if treatment has been long enough to cause adrenal suppression.
Other immunosuppressive medications can be used to allow earlier reduction of prednisone dose, and potentially improve controlled immunosuppression. In our practice, we combine prednisone with azathioprine (2 mg/kg q 24h) in all canine cases of IMHA, and add cyclosporine-A (5 mg/kg IV or PO q24h) if repeated transfusion necessary after 48 hours. In smaller patients, it may be easier to dose cyclosporine-A than azathioprine. In rare cases, mycophenolate (10 mg/kg PO q8h) is used when azathioprine and cyclosporine have not provided adequate immunosuppression after 5-7 days. Vomiting and bone marrow suppression are potential side effects in addition to increased risk for infection. In cats, prednisolone is usually effective without the addition of cytotoxic drugs.
Results of infectious disease testing may not be readily
available; therefore, it is reasonable to treat for regional tick-borne infections with doxycycline, pending results. Concurrent long term therapy with antimicrobials is not indicated without evidence of infection, as this practice promotes antimicrobial resistance.
RBC destruction also results in liberation of cell membrane phospholipid and additional microparticles, which are potent initiators of endothelial damage, inflammation and coagulation. This can result in both arterial and venous thrombosis, problems that more commonly manifest
after identification of IMHA and initiation of treatment. Anticoagulation using platelet inhibitors (e.g. clopidogrel 1-5 mg/kg q 24h PO and/or aspirin [0.5 mg/kg q 24h PO]) and coagulation factor inhibitors such as unfractionated heparin (UFH), or low molecular weight heparin (LMWH; enoxaparin, dalteparin) may also be considered. Fixed doses of UFH (150 IU/kg SC q6-8h) in dogs with IMHA appears to convey variable and inadequate therapeutic levels to sufficiently suppress Factor Xa activity. Individual adjusted dosing based on weekly monitoring of Factor XA activity appears to provide more reliable plasma heparin levels, and may
be associated with reduced mortality. LMWH have not been yet shown to be reliable and easy to dose in ill dogs and cats and/or are relatively expensive. Rivaroxaban,
and oral, direct Factor Xa inhibitor, may prove to be useful in the future. Factor Xa analysis is only available through
a single lab, Cornell University Comparative Coagulation Lab. Platelet inhibitors and heparin should be avoided if a thrombocytopenia is already present. Treatment is generally required for several months, and medication is slowly tapered based on laboratory test results.
Although the risk of immunosuppressive treatment is less than the effects of IMHA, life-threatening side effects of the medication can occur. Splenectomy in the case of refractory IMHA has been described in a small number of dogs. Human IVIG has also been used in cases of canine IMHA, but has not been proven to be more effective
than immunosuppression alone in the small number of cases reported. This contrasts with its use in presumed immune-mediated thrombocytopenia, where there may be a faster recovery, decreased need for transfusion, and decreased hospital stay with Human IVIG administration.
Prognosis of IMHA is variable and unpredictable. Fatalities are reported in 20-70% of cases, most occurring within the first 2 weeks of initiating treatment. Thrombosis has been identified in up to 80% of cases
at post mortem. Success of treatment depends on the underlying disease process, organ dysfunction, response to therapy, or side effects to treatment, and rapid identification and institution of therapy in the ER may make a difference.
Available on request

   92   93   94   95   96