Haemostasis & Bleeding Disorders

Haemostasis & Bleeding Disorders

• Haemostasis is the prevention of blood loss or stoppage of bleeding.
• Haemostasis is a process of forming clots in the walls of damaged blood vessels to prevent blood loss, maintaining blood in a fluid state within the vascular system.

Major Components of Haemostasis

• Vascular injury initiates haemostasis.
• Collagen and tissue factor are involved.
• Platelet activation leads to a platelet plug (primary haemostasis).
• Coagulation cascade (secondary haemostasis) results in blood clot formation, involving thrombin, fibrinogen, and fibrin.
• Antithrombotic mechanisms control clot formation.
• Fibrinolysis and clot degradation are part of the process.

Platelets (Thrombocytes)

• Platelets are small, non-nucleated oval cells.
• They are formed in bone marrow.
• Normal platelet count is 150,000 - 450,000 cells/cmm.
• Platelets have a lifespan of 8 days.
• Platelets are activated when they encounter damaged blood vessel walls or abnormal surfaces.

Platelet Plug Formation

• Platelet adherence (platelets attach to damaged vessel wall).
• Platelet activation (platelets become activated and release substances).
• Platelet aggregation (activated platelets clump together forming a plug).

Haemostasis Stages

• Vascular spasm: Narrowing of the blood vessel.
• Platelet plug formation: Platelets aggregate at injury site.
• Blood clot formation (coagulation): A fibrin mesh forms, trapping blood cells. Clot retraction strengthens the clot.

Blood Clot (Coagulation) Formation

• If there is a large hole, a blood clot is needed.
• The clot begins to develop few seconds after the injury.
• Coagulation pathways: Intrinsic and extrinsic pathways lead to the common pathway, culminating in thrombin converting fibrinogen to fibrin.

Blood Coagulation (clotting)

• Three main steps: formation of prothrombin activators, conversion of prothrombin into thrombin, conversion of fibrinogen into fibrin threads.

Intrinsic vs Extrinsic Pathways

• Intrinsic pathway: Activated when blood contacts a rough surface.
• Extrinsic pathway: Activated when blood comes into contact with material from damaged tissues.
• Both pathways converge at a shared pathway, leading to clot formation.

Classification of Bleeding Disorders

• Blood vessel defects: Hereditary (e.g., hereditary hemorrhagic telangiectasia), Connective tissue diseases (e.g., Marfan's syndrome, Ehlers-Danlos syndrome), Acquired (e.g., severe infections, drugs).
• Platelet defects: Thrombocytopenia (decreased platelet production or destruction), Decreased platelet function (e.g., Bernard-Soulier syndrome).
• Coagulation defects: Hereditary (e.g., hemophilia A, B, Von Willebrand disease), Acquired (e.g., anticoagulants, liver disease, DIC).

Thrombocytopenia

• Thrombocytopenia is caused by a decrease of circulating platelets.
• It is characterised by spontaneous skin purpura & hemorrhage & prolonged bleeding after trauma.

Causes of Thrombocytopenia

• Failure of platelet production (e.g., bone marrow failure).
• Increased platelet consumption (e.g., immune-mediated thrombocytopenia, disseminated intravascular coagulation).

Haemophilia

• A group of inherited blood disorders with a lifelong defect in clotting.
• Caused by a deficiency or absence of functional coagulation factor VIII (Haemophilia A) or factor IX (Haemophilia B).

Haemophilia Inheritance

• X-linked recessive trait.
• Inherited through the X chromosome.
• Common in males.
• Females can be carriers.

Haemarthrosis

• Haemarthrosis describes bleeding into a joint. A characteristic symptom of severe haemophilia.

Blood Transfusion

• A common medical procedure.
• Stored in components such as packed red blood cells (PRBCs), individual factor concentrates and fresh frozen plasma (FFP), and platelet concentrates.

Indications for Blood Transfusion

• Loss of large amount of blood as in hemorrhage
• Severe anemia
• Severe leucopenia (decreased WBCs)
• Thrombocytopenic purpura (decreased platelets)
• Haemophilia.

Complications of Blood Transfusion

• Febrile reactions
• Transfusion-associated circulatory overload
• Allergic reaction
• Infections (e.g., hepatitis C)
• Human immunodeficiency virus infection.
• Fatal hemolysis (ABO incompatibility)

Anticoagulants

• In vitro anticoagulants: Used outside the body to prevent clotting (e.g., smooth siliconized containers, oxalate compounds, citrate compounds, heparin).
• In vivo anticoagulants: Used inside the body to prevent clotting (e.g., heparin, coumarin).