Hemostasis phases

Primary hemostasis is the first phase of hemostasis consisting of platelet plug formation at the site of injury. It occurs within seconds and stops blood loss from capillaries, arterioles, and venules. Secondary hemostasis, in contrast, requires several minutes to be complete and involves the formation of fibrin through the coagulation cascade. 

HEMOSTASIS THROMBOSIS HAVE THREE COMMON PHASES... 

In hemostasis, there is initial vasoconstriction of the injured vessel, causing diminished blood flow distal to the injury. Then hemostasis and thrombosis share three phases ... 

A number of laboratory tests are available to measure the phases of hemostasis described above. The tests include platelet count, bleeding time, activated partial thromboplastin time (aPTT or PTT), prothrombin time (PT), thrombin time (TT), concentration of fibrinogen, fibrin clot stabifity, and measurement of fibrin degradation products. The platelet count quantitates the number of platelets, and the bleeding time is an overall test of platelet function. aPTT is a measure of the intrinsic pathway and PT of the extrinsic pathway. PT is used to measure the effectiveness of oral anticoagulants such as warfarin, and aPTT is used to monitor heparin therapy. The reader is referred to a textbook of hematology for a discussion of these tests. 

Little intravascular coagulation of blood occurs in normal physiological conditions. Hemostasis involves the interplay of three procoagulant phases vascular, platelet, and coagulation) that promote blood clotting to prevent blood loss (Fig. 22.1). The fibrinolytic system prevents propagation of clotting beyond the site of vascular injury and is involved in clot dissolution, or lysis (Fig. 22.2). 

In human medicine, starches with smaller average molecular weights have less profound effects on hemostasis (Treib et al 1999). This may also be the case in horses, although only one dose has been tested. In healthy horses, a 8ml/kg dose of a 10% pentastarch solution resulted in a slight decrease in the thrombin time 12 h after administration, which returned to normal after 24 h. No effect on prothrombin time or partial thromboplastin time was documented (Meister et al 1992). In healthy horses, the initial phase half-life of pentastarch is 5.6 h and the terminal phase half-life is 122 h. However, the effects on PCV, plasma total solids and plasma viscosity appear to last only 12-24 h (Meister et al 1992). In equine clinical cases, the half-life may be as short as 2h (Hermann et al 1990). Pentastarch, although available in the USA, is only approved for leukapheresis in human medicine. 

As a natural constituent of connective tissue and major structural protein, collagen is implicated in all phases of the wound healing process (hemostasis, inflammation, migration, proliferation and maturation) and controls the cellular functions such as cell shape and differentiation, migration, and synthesis of a number of proteins [100]. The use of collagen dressings may seem attractive in view of their functions to ... 

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