Chapter Two Haemorrhagic Disorders and Fibrinolysis

This chapter discusses normal and disordered haemostasis, its diagnosis and treatment, and reviews the current status of thrombolytic therapy. The function of the normal haemostatic mechanism is to prevent blood loss from intact vessels and to stop excessive bleeding from severed vessels. The arrest of bleeding following trauma is controlled by three interrelated mechanisms. These are (1) the reaction of the blood vessel wall to injury, (2) the formation of a haemostatic plug of platelets at the site of injury, and (3) blood coagulation. The fibrinolytic enzyme system plays an important role in maintaining the fluidity of blood and in contributing to the wound repair. The blood coagulation mechanism is linked to two other important defence mechanisms, namely, the inflammatory response and fibrinolysis. These three processes are initiated by activated Factor XII, which promotes (a) the formation of contact product in the coagulation system, (b) the conversion of plasminogen to plasmin in the fibrinolytic system, and (c) the activation of the kinin system. The kinin system is activated through the conversion of kallikreinogen to kallikrein; this latter enzyme converts circulating kininogen to kinin. The kinins are vasoactive substances that increase vessel permeability, produce pain and activate the complement system. The vascular disorders are a heterogeneous group of conditions that are characterized by easy bruising and spontaneous bleeding from small vessels.