Haemostasis Overview and Importance

What is Haemostasis?

• The process of stopping bleeding
• Multiple processes occur when a blood vessel is damaged
• Important because blood is essential for organ nourishment and rapid blood loss can be life-threatening

Why is Haemostasis Important?

• When injured, rapid blood loss must be stopped
• Blood is a connective tissue essential for nourishing organs

Consequences of Rapid Blood Loss

• Minor Loss: Homeostatic mechanisms maintain blood volume and cell count
• Moderate Loss: Symptoms include headache, fatigue, nausea, sweating, and dizziness
• Severe Loss: Symptoms include clammy, cold, pale skin, rapid, shallow breathing, rapid heart rate, weakness, confusion, weak pulse, little or no urine output, blue lips and fingernails, light-headedness, loss of consciousness, and death

Stages of Haemostasis

• Primary Haemostasis: Includes vasoconstriction and platelet plug formation
• Secondary Haemostasis: Includes coagulation - the formation of a fibrin mesh

Primary Haemostasis

• Vasoconstriction: Blood vessels constrict, reducing blood flow. Platelets adhere to the damaged vessel wall and release serotonin (5-HT) and thromboxanes, which cause smooth muscle contraction.
• Platelet Plug Formation: Platelets clump around exposed collagen fibers, forming a plug. von Willebrand factor stabilizes the plug.
• Platelets release adenosine diphosphate (ADP), attracting other platelets to the site.

Bleeding Time

• Measures the time required for primary haemostasis (vessel constriction and platelet plug formation)
• Normal range is 2-7 minutes
• Prolonged bleeding time can be caused by thrombocytopenia, severe anemia, collagen disorders (e.g., Ehlers-Danlos syndrome), von Willebrand’s disease, or antiplatelet drugs (e.g., aspirin, clopidogrel).

Secondary Haemostasis

• Coagulation: A complex process involving the clotting cascade, which results in the formation of insoluble fibrin strands that stabilize the platelet plug.
• Fibrin Formation: Soluble fibrinogen is converted to insoluble fibrin through the clotting cascade.
• Fibrin Mesh: The fibrin mesh traps red and white blood cells, forming a clot.

Coagulation Cascade

• Extrinsic Pathway (Tissue Factor Pathway): triggered by tissue factor (factor III) released from damaged endothelial cells. Tissue factor converts factor VII to VIIa, which activates factor X to factor Xa, leading to the common pathway. Measured by Prothrombin Time (PT), with a normal value of 11-16 seconds.
• Intrinsic Pathway (Contact Pathway): triggered by exposure of blood to collagen fibers in the damaged vessel. Starts with activation of factor XII, which, upon exposure to collagen, becomes factor XIIa and initiates the clotting cascade. Measured by Activated Partial Thromboplastin Time (aPTT), with a normal value of 25-35 seconds.

Dental Relevance

• Dental procedures can cause bleeding
• Bleeding should stop naturally within 4-10 minutes depending on the wound.
• There are many causes of prolonged bleeding, which are addressed in a separate lecture
• Bleeding in dentistry can be controlled by applying pressure, sutures, packing with hemostatic agents (e.g., Surgicel), electrosurgery units, or lasers.

Summary

• Haemostasis is a vital process that stops bleeding and involves primary (vasoconstriction and platelet plug formation) and secondary (coagulation) phases
• The clotting cascade is critical for fibrin formation and clot stabilization
• Understanding haemostasis is important for dental hygienists and therapists who need to manage bleeding during dental procedures

Haemostasis

• The process of stopping bleeding
• Involves three stages: vasoconstriction, platelet plug formation, and coagulation

Vasoconstriction

• Blood vessels constrict to reduce blood loss
• Mediated by factors like serotonin and thromboxanes released by platelets

Platelet Plug Formation

• Platelets adhere to exposed collagen in damaged vessel walls
• Von Willebrand factor facilitates platelet adhesion
• Platelets release ADP and other factors to attract more platelets, forming a temporary plug

Coagulation

• A complex cascade of events leading to fibrin formation
• Fibrin strengthens the platelet plug, forming a stable clot

Clotting Cascade

• Two pathways converge to form a common pathway:
  • Extrinsic pathway: Triggered by tissue factor (Factor III)
    • Measured by Prothrombin Time (PT)
  • Intrinsic pathway: Triggered by blood exposure to collagen
    • Measured by Activated Partial Thromboplastin Time (aPTT)
• Common pathway:
  • Prothrombin is converted to thrombin
  • Thrombin converts fibrinogen to fibrin
  • Fibrin forms a mesh, stabilizing the clot

Clot Retraction

• Occurs within 24 hours
• Clot shrinks by about 90%
• Pulls the edges of the wound together

Clot Breakdown (Fibrinolysis)

• Plasminogen, a precursor trapped in the clot, is converted to plasmin
• Plasmin breaks down fibrin
• Thrombin-activated fibrinolysis inhibitor (TAFI) stabilizes clots by inhibiting fibrinolysis

Dental Relevance

• Dental procedures often cause minor hemorrhage
• Knowledge of haemostasis is crucial for managing bleeding effectively
• Typical bleeding stops within 4-10 minutes
• Dental tools like pressure, sutures, haemostatic agents, electrosurgery, and lasers can be used to control bleeding

Clotting Disorders

• Haemophilia (A, B, C) causes deficiencies in clotting factors like Factor VIII, IX, and XI.

Anticoagulants

• Medications like Warfarin, Heparin, and Rivaroxaban interfere with the clotting cascade.
• Their use in dental patients requires careful management to prevent excessive bleeding

Bleeding Time

• Time taken for primary haemostasis (vasoconstriction and platelet plug formation)
• Normally 2-7 minutes
• Prolonged in conditions like thrombocytopenia, von Willebrand disease, and anti-platelet drug use

Fibrinolysis Abnormalities

• Enhanced fibrinolysis: Seen in conditions like DIC and metastatic prostate cancer
• Depressed fibrinolysis: Occurs in conditions like alcoholic liver disease, antiphospholipid syndrome, hypothyroidism, chronic renal disease, and pregnancy

Thrombosis

• Formation of a blood clot (thrombus) within a blood vessel
• Caused by overactive coagulation or underactive fibrinolysis
• Most often begins at sites of endothelial damage

Haemorrhage in Dentistry

• Usually managed with:
  • Pressure
  • Sutures
  • Haemostatic agents
• Less common methods include electrosurgery and lasers

Coagulation Factors and Vitamin K

• Most clotting factors are synthesized in the liver
• Vitamin K is essential for the formation of several clotting factors (Factors II, VII, IX, and X)
• Liver disease can impair clotting factor production, leading to bleeding disorders

Summary of the Coagulation Cascade

• Extrinsic and intrinsic pathways converge on the common pathway
• Prothrombin is converted to thrombin
• Fibrinogen is converted to fibrin, forming a stable clot
• Extrinsic pathway is triggered by tissue damage and measured by PT
• Intrinsic pathway is triggered by blood exposure to collagen and measured by aPTT

This quiz covers the essential processes of haemostasis, the body's mechanism for stopping bleeding. It explores the importance of rapid blood loss management and the consequences associated with varying degrees of blood loss. Understand the stages of haemostasis and their significance for organ nourishment.