Practical in-clinic hemostasis (Proceedings)


Practical in-clinic hemostasis (Proceedings)

Nov 01, 2009

Hemostasis results through a complex interaction between platelets, blood vessel wall and coagulation factors. This system is also intimately tied to inflammatory responses so that diseases that are associated with significant inflammation will also activate the hemostatic system, for instance sepsis, infectious canine hepatitis, FIP, and IMHA. The ultimate goal of the hemostatic system is to form a clot to prevent further hemorrhage. Counterbalancing the clotting reaction is fibrinolysis and a variety of proteins meant to inactivate active clotting factors. This helps limit clotting to the area where it is needed. Hemostasis can be divided into primary hemostasis, coagulation and fibrinolysis. By knowing the clinical signs of various hemostatic problems and a few simple in house tests it is often possible to narrow down the cause of abnormal hemorrhage and be able to develop an appropriate therapeutic and diagnostic plan.

Primary hemostasis

This is a result interaction between blood vessel walls and platelets and functions to seal small and large rents in vessels rapidly. Effective primary hemostasis is dependent upon platelet numbers, platelet function, vessel wall integrity and the presence of von Willebrand factor (vWf). As a result defects in any of these areas can result in problems forming an initial platelet plug. Petechia, ecchymoses, epistaxis, hyphema, pinpoint retinal hemorrhages, and hematuria are the typical clinical signs. It is rare to see extensive bruising or hemorrhage into body cavities (thorax, pericardium, abdomen, joint).

The most commonly seen problem of primary hemostasis is thrombocytopenia. This can be caused by decreased production (bone marrow disease, Ehrlichia, neoplasia, estrogen), increased use (or loss as through DIC, hemorrhage, rat poison) or increased destruction (immune-mediated thrombocytopenia, Ehrlichia).

It is also possible, though rare, to see problems with platelet function. There are congenital diseases that have been identified though they are uncommon. More common are acquired platelet function defects. The use of aspirin can result in platelet function problems. Thrombocytopathies can also be seen when abnormal proteins coat the platelets (usually a gammopathy), this is occasionally encountered with Ehrlichia or multiple myeloma. If a procedure is planned that could be associated with hemorrhage in an animal with a significantly elevated globulin level, I do recommend a buccal mucosal bleeding time (BMBT) be performed first.

Vasculitis tends to relatively rare. It can be seen with rickettsial diseases such as Rocky Mountain Spotted Fever or FIP. Generally these diseases cause DIC by having widespread endothelial damage.

Von Willebrand disease represents the most common inherited hemostatic disorder encountered. There are various forms of the disease depending upon whether all forms of vWf are reduced, only the large multimeres are missing or there is no vWf at all. The disease is common in Dobermans, although it is rare to see spontaneous clinical bleeding. Usually these animals just tend to ooze more. In the severe forms of vWd as seen in Scotties and other breeds it is possible to see fatal hemorrhages. Generally the most severe forms of the disease tend to cause premature death at an early age so that it is rarely seen in practice. Genetic testing is available for some forms of the disease, though data from most of these tests have not been subjected to peer review scrutiny.