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Veterinarian Technician November 2012 (Vol 33, No 11)

Equine Essentials: Disseminated Intravascular Coagulation in Horses

by Jamie DeFazio, AS, CVT, VTS (EVN)

    Disseminated intravascular coagulation (DIC) is the most commonly seen hemostatic disorder in horses.1 Affected horses are considered to be critically ill. DIC develops secondary to a primary disease—most commonly, gastrointestinal disease or sepsis. DIC can also develop secondary to neoplasia, renal disease, or hemolytic anemia. Because DIC is often initially subclinical, some clinicians recommend (1) regular monitoring of high-risk patients by coagulation profile screening2 and (2) treatment of DIC as early as possible. Delayed detection and treatment contribute to a high mortality rate and secondary complications such as laminitis. Performing clotting profiles daily may become expensive, and because the results must be significantly abnormal to definitively diagnose DIC, many veterinarians choose to initiate treatment based on the clinical “picture.”

    DIC changes as it progresses, making it difficult to diagnose and treat. The primary disease process triggers the coagulation cascade and initially causes a hypercoagulable state, resulting in clot formation. Once the clotting factors and platelets are consumed by coagulation, affected animals enter a hypocoagulable state, putting them at risk for life-threatening hemorrhage and multiple organ failure.

    Clinical Signs

    The Hypercoagulable State

    As subclinical DIC progresses to the clinical form, a commonly observed clinical sign is venous thrombosis. All veins are at risk, particularly those used for venipuncture or intravenous catheterization. In some cases, distal limb circulation may be affected, causing swelling and lameness due to thrombosis.3

    The Hypocoagulable State

    As the platelets and clotting factors are consumed, the clinical picture becomes more serious. One early sign is prolonged bleeding at venipuncture or intravenous catheter sites. Petechiation (small purple spots caused by microvascular hemorrhage) is often observed on the mucous membranes; this can be a clinical sign of thrombocytopenia. A coagulation profile should be obtained to substantiate a diagnosis of DIC. Depending on the treatment or progression of the underlying disease(s)/condition(s), hemorrhage may be seen from various sites, such as the uterus, surgical sites, or the nares. The hemorrhage is often difficult to control and can be life threatening. There may be signs of other organ dysfunction, such as renal or hepatic disease, due to microvascular thrombosis.

    Diagnostic Testing

    Large animals with evidence of endotoxemia should be monitored closely for clinical signs of DIC, including venous thrombosis, petechiation, and prolonged bleeding. Once DIC becomes clinical, the prognosis worsens. If a clotting profile is performed during early DIC, coagulopathy may not be evident. Later in the course of the disease, although a diagnosis cannot be made using a single blood test, it can be supported by obtaining at least three abnormal clotting values within the diagnostic period.4 Some clinical laboratory tests are outlined below.

    Fibrinogen Testing

    Fibrinogen is an acute-phase protein and a sensitive marker of systemic inflammation in large animals, so the fibrinogen level should always be interpreted in the context of concurrent disease processes. Normal fibrinogen values for horses are 200 to 400 mg/dL.1 In some cases of early DIC, the fibrinogen level may be increased due to the inflammatory nature of the underlying disease process. As DIC progresses, hypofibrinogenemia is often seen. 

    Platelet Count

    The platelet count can be low in horses with DIC. A normal platelet count is >100,000/µL; when the platelet count drops to <40,000/µL, patients usually begin to show clinical signs such as prolonged bleeding time and hematoma formation after minor trauma. Petechiation may be seen on the oral mucous membranes of thrombocytopenic patients.

    Prothrombin Time

    Activity of the extrinsic and common coagulation pathways is measured by the prothrombin time (PT). In animals with DIC, PT can be prolonged. Normal PT in horses is approximately 8 to 13 seconds,5 but the normal reference range varies according to the facility performing the test.

    Activated Partial Thromboplastin Time

    Activated partial thromboplastin time is an indicator of the function of the intrinsic and common coagulation cascades. In healthy animals, the activated partial thromboplastin time is approximately 30 to 60 seconds, but it can be prolonged in horses with DIC.6 As with the PT, the normal reference range varies according to the facility performing the test.

    Fibrinogen Degradation Products

    Fibrinogen degradation products result from the breakdown of blood clots; therefore, an increase in the number of fibrinogen degradation products indicates increased clot formation as well as breakdown due to lysis.

    Treatment and Prevention

    Treating the primary disease process is essential to treating DIC and stopping its progression. Because most horses that develop DIC have had a septic or toxic insult, much of the initial patient support involves stabilization using intravenous fluids, antiendotoxic agents, and antiinflammatory medications (e.g., flunixin meglumine) as well as other treatments specific to the underlying disease(s)/condition(s).

    Administration of intravenous crystalloid and colloid fluids is important for treating dehydration, replacing electrolytes, and improving tissue perfusion. In some cases of shock, use of hypertonic saline may increase vascular perfusion by drawing in extravascular fluid to expand the vascular space, but use of hypertonic saline is controversial in patients with DIC-associated bleeding because the saline may exacerbate bleeding. Aminocaproic acid, an antifibrinolytic agent, is contraindicated for treating DIC because it may enhance hypercoagulation. To replace coagulant and anticoagulant proteins, fresh plasma or whole blood can be administered to treat life-threatening hemorrhage due to DIC. Some clinicians administer heparin within a unit of plasma to achieve antithrombin activation.

    Preventing DIC in at-risk patients is key. Heparin is a commonly used preventive in equine patients. Low-molecular-weight heparin is more effective at reducing thrombus formation and has fewer adverse effects than unfractionated heparin.1,7 Administering heparin before DIC develops or during early DIC may prevent clot formation.

    Conclusion

    Early DIC is likely underdiagnosed in critically ill equine patients. The prognosis for patients with DIC depends on the successful treatment of the underlying disease(s)/condition(s) and the speed and severity of the progression of DIC. Once signs of a bleeding diathesis are evident, the prognosis for affected patients is poor. Therefore, early recognition and effective treatment of the primary disease are key to a positive outcome.

    Ms. DeFazio discloses that she is a consultant for International WIN, ltd. She is also the Equine Essentials section editor for Veterinary Technician.

    1. Monreal L. Treating disseminated intravascular coagulation. Compend Equine Contin Educ Vet 2008;3(6):326-330.

    2. Kahn C. Monitoring procedures for the critically ill animal. In: The Merck Veterinary Manual. 9th ed. Philadelphia, PA: National Publishing; 2005:1412-1413.

    3. Reed S, Hubbell J, Latimer C, et al. In: Rood and Riddle Equine Hospital Formulary of Medications in Use and Laboratory Manual. Lexington, KY: Rood and Riddle Equine Hospital; 2011:243, 284-286.

    4. French TW, Blue JT, Stokol T. Fibrin(ogen) degradation products. In: Hemostasis: Tests of Hemostasis. http://ahdc.vet.cornell.edu/clinpath/modules/coags/fdps.htm. Ithaca, NY: Cornell University. Accessed June 2012.

    5. Orsini J, Divers T. Blood coagulation disorders. In: Manual of Equine Emergencies, Treatments and Procedures. Philadelphia, PA: Saunders; 2003:340-342.

    6. Colahan P, Mayhew I, Merritt A, et al. Hemolymphatic system. In: Manual of Equine Medicine and Surgery. St. Louis, MO: Mosby; 1999:513-514.

    7. Dolente B, Wilkins P, Boston R. Clinicopathologic evidence of disseminated intravascular coagulation in horses with acute colitis. J Am Vet Med Assoc  2002;220(7):1034-1038.

    References »

    NEXT: Final View: A Not-So-Safe Safety Pin

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    Did you know... Disseminated intravascular coagulation is the most commonly seen hemostatic disorder in horses.Read More

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