The coagulation system and blood clot stability

Perioperative hemorrhage is one of the major challenges in the care of patients undergoing surgical and other invasive procedures. The etiologies can include technical difficulties and complications of surgery, and coagulation abnormalities. The coagulation cascade, a very dynamic process involving series of enzymatic reactions, is pivotal to a normal blood circulation and hemostasis. Hemostasis can be achieved by activation of intrinsic pathway or extrinsic pathway. It is also critical to maintain a delicate balance between the clot formation and the fibrinolysis. Hemostasis can be categorized as primary hemostasis (platelets adhere to the site of injury) and secondary hemostasis (coagulation activation leading to fibrin and clot formation). The normal coagulation process can include three phases: the initiation phase, the amplification phase and the propagation phase. The most important regulation mechanisms in coagulation are their multiple zymogens and cofactors all requiring activation prior to exerting their effects. The basic principle of clot stability is maintaining a balance between clot formation and fibrinolysis. This balance is regulated by numerous factors including molecular, metabolic, mechanical, and pharmacologic. And the processes of coagulation and fibrinolysis frequently occur simultaneously in many clinical scenarios. The many steps in coagulation and fibrinolysis can also be the targets for pharmacological interventions.