Page 1265 - Small Animal Internal Medicine, 6th Edition

CHAPTER 73 Common Immune-Mediated Diseases 1237

were administered together with glucocorticoids compared regimen for thromboprophylaxis based on measurement of
with prednisone alone. Cost is often a deterrent to using anti-Xa activity is associated with a better outcome in dogs
VetBooks.ir hIVIG, and there is potential for sensitization to human with IMHA rather than a fixed dose of 150 U/kg SC q6-8h
heparin (Helmond et al., 2010). (For a discussion of the use
proteins, so caution is advised when administering more
of low-molecular-weight heparin, see Chapter 87.) Low-dose
than one dose.
aspirin (0.5 mg/kg PO q24h) has also been used to prevent
BLOOD TRANSFUSION thromboembolic complications in dogs with IMHA. Weinkle
Most dogs and cats with acute, severe IMHA need oxygen- et al. (2005) reported that dogs treated with a protocol that
carrying support. Oxygen supplementation alone is of included prednisone, azathioprine, and low-dose aspirin
limited benefit. The need for blood transfusion depends on had the longest survival times. Low-dose aspirin may not
the severity, rate of onset and chronicity of the anemia, and result in appropriate platelet inhibition in all dogs. Aspirin
the presence and severity of concurrent disease such as pul- resistance was identified in 30% of dogs in one study, yet
monary thromboembolism and gastrointestinal blood loss. another 30% experienced only partial responsiveness to low-
No specific hematocrit level should be used as a transfusion dose aspirin. Clopidogrel bisulfate is an inhibitor of the ADP
trigger; rather, each patient should be considered individu- receptor on platelets and is the gold standard for prevention
ally. In general, transfusion should be considered when the of cardiogenic arterial thromboembolism in cats. Clopido-
dog has problems with tachycardia, tachypnea, anorexia, grel was compared with low-dose aspirin, prospectively, in a
lethargy, or weakness while at rest. Most dogs with acute group of dogs with IMHA, and survival was similar between
IMHA and a hematocrit less than 15% have some degree of the two groups. (See Chapters 12 and 87 for more informa-
tissue hypoxia and will benefit from a blood transfusion tion on treatment and prevention of thromboembolism.)
regardless of how the dog appears clinically. Severe tissue
hypoxia likely exacerbates the complications of IMHA, such SUPPORTIVE CARE
as hepatic necrosis, DIC, and thromboembolism. Aggressive supportive care is critical to a good outcome in
Transfusion of packed RBCs (pRBCs) is ideal; whole dogs with IMHA. Identification and treatment of underlying
blood is acceptable but less ideal because the plasma com- disease, detection of complications associated with immuno-
ponent is not necessary and may increase the risk of a trans- suppressive drug therapy, and good nursing care positively
fusion reaction. (See Chapter 82 for more information about influence outcome. In addition to transfusion, fluid therapy
blood transfusions.) should be administered in dogs with evidence of dehydra-
tion to improve tissue perfusion. In dehydrated dogs, fluid
PREVENTION OF THROMBOEMBOLISM therapy will decrease the measured hematocrit, but this does
The majority of dogs with IMHA are hypercoagulable on not change the total RBC mass. Fluid therapy should not be
presentation as assessed by thromboelastrography (TEG), withheld because of fear of exacerbating anemia. In reality,
a viscoelastic assessment of coagulation, and some have fluid therapy reveals the true severity of the anemia.
evidence of DIC. Abnormalities of the hemostatic system Careful investigation and treatment of underlying disease
that have been identified include prolongation of activated in dogs with IMHA is important. Immunosuppressive
partial thromboplastin time (aPTT) and prothrombin time, therapy is usually still necessary in dogs with secondary
increased D-dimer, increased fibrinogen degradation prod- IMHA. However, the duration of immunosuppression may
ucts (FDPs), decreased antithrombin (AT) concentration, be shorter if an underlying cause can be identified and
and hyperfibrinogenemia. treated. If an infectious disease is identified, addition of
Thromboembolic events (TEs) are a common compli- adjunctive immunosuppressive drugs should be avoided.
cation and important cause of death in dogs with IMHA. Complications of immunosuppressive drug therapy
TEs have been documented at necropsy in 29% to 100% of include bone marrow suppression, infection, gastrointestinal
dogs with IMHA. Intravenous catheter placement and iden- ulceration, and iatrogenic hyperadrenocorticism. Gastro-
tification of certain clinicopathologic abnormalities, such as intestinal hemorrhage can contribute to anemia in dogs with
thrombocytopenia, hyperbilirubinemia, leukocytosis, and IMHA, either from the gastrointestinal effects of high doses
hypoalbuminemia, are associated with an increased risk of of glucocorticoids or concurrent thrombocytopenia, vascu-
TE in dogs with IMHA. The pathogenesis of thrombus for- litis, ischemia, or other concurrent disease. Recognition of
mation is unknown, and effective regimens for prophylaxis occult gastrointestinal hemorrhage is important because the
have not been established. Treatment options currently used resulting anemia may be confused with a failure to respond
for prevention of thromboembolic complications include to treatment for IMHA (see Chapter 80). Drugs used for
heparin, low-molecular-weight heparin, aspirin, clopidogrel, treatment of gastrointestinal hemorrhage include gastro-
or a combination of these modalities. The recommended intestinal protectants such as sucralfate, H 2 blockers (e.g.,
starting dose for heparin in patients with IMHA is 200 to famotidine), and proton pump inhibitors (e.g., omeprazole).
300 U/kg subcutaneous (SC) q6h, and the dose is adjusted by
measuring anti-Xa activity (0.35-0.7 U/mL) or, less ideally, Prognosis
monitoring the aPTT with the aim to prolong aPTT by 25% In approximately 60% of dogs with IMHA, medications can
to 50% of baseline. An individually adjusted heparin dosing ultimately be discontinued after a slow tapering of the