hemostasis

Overview of Hemostasis

  • Definition: Hemostasis refers to the arrest of bleeding or prevention of blood loss following injury to a blood vessel.

  • Importance: It is crucial for the body to react and respond to injuries (e.g., cuts) to prevent excessive blood loss.

Structure of Blood Vessels

  • Arteries:

    • Function: Carry oxygenated blood away from the heart to the body.

    • Characteristics:

    • Carry blood under high pressure, hence have thick elastic walls.

    • Do not have valves.

    • Blood pressure measurement reflects arterial pressure.

    • The pulse felt in arteries indicates blood flow.

  • Veins:

    • Function: Return deoxygenated blood to the heart.

    • Characteristics:

    • Operate under low pressure; hence when injured, blood oozes rather than spurts.

    • Have thinner walls than arteries and contain valves to prevent backflow.

    • Visible through the skin surface, often appearing bluish due to deoxygenation.

    • Do not have a pulse.

  • Capillaries:

    • Function: Site of gas, nutrient, and waste exchange.

    • Characteristics:

    • Smallest type of blood vessels with tiny diameters.

    • Susceptible to damage (e.g., resulting in petechiae).

Overview of Platelets (Thrombocytes)

  • Normal Count: 150,000 to 400,000 platelets per cubic millimeter.

  • Production:

    • Platelets are produced in the bone marrow.

    • Stored in the liver and spleen for ready access during hemorrhaging.

  • Lifespan: 7 to 12 days; undergo apoptosis upon expiry.

  • Macrohages: Responsible for cleaning up the dead platelets.

  • Laboratory Test: Platelet count is a part of the Complete Blood Count (CBC).

Coagulation Cascade

  • Concept: The cascade is triggered by either external tissue trauma or internal vessel damage.

  • Pathways:

    • Extrinsic Pathway:

    • Triggered by external injury leading to the immediate release of coagulation factors from the liver.

    • Measured by PT (Prothrombin Time) test, normal range: 11 to 13.5 seconds.

    • Intrinsic Pathway:

    • Activated by internal vessel damage.

    • Measured by aPTT (Activated Partial Thromboplastin Time) test, normal range: 25 to 35 seconds.

  • Common Pathway: Coagulation factors converge to form fibrin, ultimately contributing to clot formation to help healing.

  • PT/INR Testing:

    • PT time assesses extrinsic pathway functionality.

    • INR indicates blood coagulation levels, especially relevant for patients on anticoagulants (e.g., warfarin).

    • Normal INR: 0.8 - 1.1; therapeutic range for anticoagulant therapy: 2 - 3.

Coagulation Disorders

  • Thrombocytopenia (Low Platelet Count):

    • Causes: Autoimmune disorders (e.g., lupus), trauma (e.g., prosthetic heart valves), dialysis (fistula), chronic alcoholism (liver damage), and chemotherapy-induced suppression of bone marrow.

  • Thrombocytosis (High Platelet Count):

    • Causes: Stress, cancers, infections, and sepsis (systemic response).

Specific Coagulation Disorders

  • Hemophilia:

    • Common Types: Hemophilia A (factor VIII deficiency) is most prevalent.

    • Symptoms: Extended bleeding, spontaneous bruising, and prolonged aPTT.

  • Vitamin K Deficiency:

    • Caused by malnutrition, poor absorption, or liver disease.

    • Involves prolonged clotting time due to the role of vitamin K in the coagulation cascade. Binds to factor VII, affecting extrinsic pathway; abnormal PT.

  • Disseminated Intravascular Coagulation (DIC):

    • Life-threatening condition where clotting and bleeding occur simultaneously, often triggered by severe trauma, burns, or septic shock.

    • Results in rapid consumption of coagulation factors and simultaneous activation of fibrinolysis.

Recognition of Bleeding Disorders

  • Petechiae: Small pinpoints of bleeding from broken capillaries, typically seen on the skin.

  • Hematomas: Larger accumulations of blood outside blood vessels, indicating significant trauma.

  • Ecchymosis: Bruises indicating bleeding under the skin due to ruptured larger vessels.

  • Purpura: Larger areas of petechiae-like discoloration on skin, indicating more extensive capillary breakage.

Conclusion and Practical Application

  • The clotting process involves primary hemostasis (temporary plug formation) and secondary hemostasis (fibrin clot formation).

  • Nurses should recognize and react appropriately to signs of bleeding, including the need for pressure dressings post-venipuncture.

  • Understanding the coagulation cascade is essential for addressing coagulation disorders and tailoring treatments accordingly.