Coagulation Defects and Anesthesia

Abstract

Summary N ormal hemsotasis is dependent on precisely regulated interactions between the blood vessel wall, platelets and plasmas clotting factors, the hemostatic mechanism includes: vascular spasm, formation of platelet plug, blood coagulation and growth of the fibrous tissue into the blood clot to close the hole in the vessel permanently, within seconds of the vessel injury, activated platelets aggregate, forming a hemostatic plug in an initial process called "primary hemostasis". It is accompanied by activation of the plasma coagulation system and the formation of a definitive fibrin clot, a process called "secondary hemostasis". The coagulation cascade consists of intrinsic and extrinsic pathways, which terminate in a final common pathway. Fibrinolytic system prevents extension of the clot formation to the surrounding tissues. Coagulation disorders either disorders of hemostasis or disorders of thrombosis. Disorders of hemostasis either be inherited or acquired, most common inherited disorders are hemophilias and von Willdebrand's disease. Hemophilias are characterized by deficiency of coagulant factors which lead to increase bleeding at surgery and in the postoperative period, hemophilias are either hemophilia A, B or C. von Willebrand's disease is an inherited bleeding disorder secondary to vWF deficiency. vWF is important for primarily in platelet adhesion to the subendothelial layer of the exposed endothelium, in addition, it carriers the factor VIII molecules in the plasma. Acquired disorders of hemostasis including multiple diseases such as, Vitamin K deficiency which is necessary for promotion of formation of four of the most important clotting factors (II, VII, IX and X). Consumption coagulopathy (DIG) which characterized by widespread small vessel thrombosis associated with generalized bleeding as a result of consumption of the coagulation factors and excessive flbrinolysis. it may occur secondary to trauma, sepsis, malignancies. Thrombocytopenia is one of the causes of excessive bleeding during surgery, it is either idiopathic or secondary to drug intake, malignancy or postinfection. Idiopathic thrombocytopenic purpura is a persistent thrombocytopenia, caused by antiplatelets immunoglobulins low platelet count. Intraoperative bleeding may reflect not only alteration in the number but also the function of circulating platelets and procoagulants. Coagulation disorders may be predisposed by pathology elsewhere include renal diseases, liver diseases, SLE or hematological malignancy. Disorders of thrombosis "hypercoagulable state" are either congenital or acquired occur when there is an imbalance between the anticoagulant and procoagulant activities of plasma in which the procoagulant activities predominate. Antithrombin III, protein C and protein S deficiencies are the most common hypercoagulable state. Evaluation of the coagulation state depends upon a proper history taking, physical examination and laboratory tests. The most commonly used are proghtombin time (PT) which evaluates the extrinsic and the common pathways, and partial thromboplastin time (PTT) which evaluates the intrinsic and the common pathways, other tests including clotting time, bleeding tine and specific estimation of the coagulation factors, also thrombo-elastography is a rapid and reliable method of testing the entire coagulation systems. Preoperatively, the patient is assessed and specific replacement therapy (e.g. FFP, cryoprecipitate, ...) is given as required.