Alterations in Hemostasis

Chapter 22: Alterations in Hemostasis

Definition of Hemostasis

  • Hemostasis: Defined as "stoppage of blood flow."

  • Abnormal Hemostasis can include:

    • Inappropriate Clotting: Formation of clots when not needed.

    • Insufficient Clotting: Failure to form clots leading to excessive bleeding.

  • Key Points:

    • The liver synthesizes coagulation factors, which are crucial for hemostasis.

    • Vitamin K is essential for the formation of several clotting factors.

Hemostatic Response to Injury

  • Initial Response:

    • When injury occurs, there is a rapid vessel spasm due to:

    • Smooth muscle contraction of the vessel wall following endothelium injury.

    • This reaction serves to minimize blood loss immediately post-injury.

  • Formation of the Platelet Plug:

    • Von Willebrand factor (vWf) causes platelets to become 'sticky’, promoting aggregation and forming a platelet plug.

Coagulation Pathways

  • Intrinsic Pathway: Activated by damage to the endothelium.

  • Extrinsic Pathway: Activated by tissue injury.

  • Common Features in Both Pathways:

    • Both pathways lead to:

    • Activation of Factor Xa which converts prothrombin into thrombin.

    • Thrombin then converts fibrinogen into fibrin, forming a fibrin mesh that stabilizes the platelet plug.

Clot Retraction and Dissolution

  • Clot Retraction: The process by which the clot contracts and stabilizes the wound site.

  • Clot Dissolution (Lysis): The process involving plasminogen activators that convert plasminogen to plasmin, which dissolves the fibrin mesh. This mechanism is vital for healing and restoring normal blood flow.

Disorders of Hemostasis

Hypercoagulability

  • Causes of hypercoagulability include:

    • Increased platelet count (Thrombocytosis).

  • Symptoms that may arise:

    • Formation of thrombus (blood clots).

    • Development of embolus (clots that travel and obstruct vessels).

Virchow’s Triad

  • Virchow’s Triad refers to three factors that increase the risk of thrombosis:

    • Stasis: Immobility or pooling of blood.

    • Endothelial Injury: Occurs from surgery or trauma to blood vessels.

    • Hypercoagulable State: Influenced by smoking, genetics, birth control use, obesity, medications, etc.

Under Coagulation and Bleeding Disorders

  • Thrombocytopenia: Defined as a decreased number of platelets (<100,000).

    • Causes:

    • Decreased production due to bone marrow dysfunction.

    • Increased destruction caused by autoimmune disorders.

    • Symptoms can include excessive bleeding, purpura, ecchymosis (bruising), epistaxis (nosebleeds).

    • Diagnosis: Based on complete blood count (CBC), prothrombin time (PT), partial thromboplastin time (PTT).

Idiopathic Thrombocytopenic Purpura (ITP)

  • Characteristics:

    • Excessive destruction of platelets primarily in the spleen and liver.

    • More common in children following viral infections and in adults without an identifiable trigger.

    • Symptoms include purpura, petechiae, and bruising.

    • Treatment options include corticosteroids, immunoglobulins, or splenectomy for severe cases.

Impaired Platelet Function

  • Conditions that can cause impaired function include:

    • Kidney disease (renal failure).

    • Drugs (e.g., NSAIDs, aspirin, heparin).

    • Conditions leading to acidosis affecting functionality.

Bleeding Associated with Coagulation Factors

  • Coagulation factors include Factors V, VII, prothrombin, and fibrinogen, which are affected by:

    • Liver disease (disrupting factor synthesis).

    • Vitamin K deficiency, which is critical for synthesis of various clotting factors.

Von Willebrand Disease

  • Characterized by:

    • A defect in the Von Willebrand factor, critical for platelet adhesion.

    • Inherited in an autosomal pattern.

    • Symptoms include abnormal bleeding tendencies, especially during surgeries.

    • Treatment includes administration of factor VIII.

Hemophilia

  • A genetic disorder characterized by deficiencies in coagulation factors, primarily Factor VIII (Hemophilia A) or Factor IX (Hemophilia B).

    • It is X-linked recessive, predominantly affecting males, although 30% of cases may occur without a family history.

    • Symptoms include bleeding into joints (hemarthrosis), gastrointestinal tract, and soft tissues.

    • Treatment involves factor infusions and education on managing bleeding episodes.

Disseminated Intravascular Coagulation (DIC)

  • A complex disorder that is a secondary complication due to various clinical conditions (e.g., sepsis, trauma).

    • Features include:

    • Massive activation of the clotting cascade.

    • Formation of widespread fibrin clots leading to occlusive phenomena, tissue ischemia, and systemic hemorrhage.

    • Symptoms can vary based on the underlying cause.

    • Treatment includes relieving the underlying condition and supporting clotting factor replacement (e.g., transfusions).

    • Potential risks include profound bleeding due to depleted clotting factors.