Courtesy: Amr Abdelgawad, Maimonaides Medical centre, NY, USA

Overview

• Regulation of blood clot formation and prevention is crucial in orthopaedic practice

• Risk factors such as:

  • Surgery

  • Trauma

  • Prolonged immobilization
    increase the likelihood of:

  • Deep vein thrombosis (DVT)

  • Pulmonary embolism (PE)

 A sound understanding of:

• Coagulation cascade

• Diagnosis of pulmonary embolism

• Antithrombotic drugs

is essential for safe perioperative management

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Coagulation Cascade

The coagulation cascade represents a series of enzymatic reactions leading to clot formation.
It consists of:

• Extrinsic pathway

• Intrinsic pathway

• Common pathway

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Extrinsic Pathway

Key Features

• Activated rapidly after tissue injury

• Initiated by tissue factor (TF) from outside the vessel

Mechanism

• Tissue injury exposes factor VII to tissue factor

• TF–factor VII complex activates factor X

Laboratory Assessment

• Prothrombin Time (PT)

• Standardized using INR (International Normalized Ratio)

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Intrinsic Pathway

Key Features

• Activated by circulating blood factors

• Slower than extrinsic pathway

Factors Involved

• Factor XII

• Factor XI

• Factor IX

• Factor VIII

Outcome

• Activation of factor X

Laboratory Assessment

• Partial Thromboplastin Time (PTT)

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Common Pathway

Convergence Point

• Both pathways meet at factor X

Sequence

• Factor X — Prothrombin — Thrombin

• Thrombin — Fibrinogen — Fibrin

• Factor XIII stabilizes fibrin

Result: Formation of a stable cross-linked fibrin clot

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Pulmonary Embolism

Pulmonary embolism is a serious and potentially fatal complication, often arising from DVT, particularly in orthopaedic patients.

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Clinical Presentation

• Shortness of breath

• Tachypnea

• Chest pain

• Tachycardia

• Hypoxia (low oxygen saturation)

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Initial Evaluation

• Chest X-ray

• ECG

• Arterial blood gas (ABG)

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Arterial Blood Gas Findings

Typical Findings

• Hypoxemia

• Hypocapnia (due to hyperventilation)

• Respiratory alkalosis

• Increased A–a oxygen gradient

Severe Cases

• Hypercapnia

• Respiratory acidosis

• Metabolic acidosis (in shock)

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ECG Findings

• Sinus tachycardia

• Possible right bundle branch block

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Laboratory Markers

• Elevated D-dimer

• Increased natriuretic peptides (due to right ventricular strain)

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Imaging in Pulmonary Embolism

CT Pulmonary Angiography (CTPA)

• Gold standard in most settings

• Direct visualization of thrombus in pulmonary arteries

• Preferred in stable patients

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Ventilation–Perfusion (V/Q) Scan

• Assesses ventilation–perfusion mismatch

• Less commonly used today

• Useful when CTPA is contraindicated

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Antithrombotic Medications

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Unfractionated Heparin (UFH)

• Large molecular compound

• Enhances antithrombin activity

• Inhibits:

  • Factor Xa

  • Thrombin (factor IIa)

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Low Molecular Weight Heparin (LMWH)

• Smaller molecules

• Activates antithrombin

Key Feature

• Greater inhibition of factor Xa than thrombin

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Fondaparinux

• Synthetic pentasaccharide

• Selectively inhibits factor Xa via antithrombin

• Does not inhibit thrombin

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Direct Factor Xa Inhibitors

Examples

• Rivaroxaban

• Apixaban

Features

• Direct inhibition of factor Xa

• Oral administration

• Do not require antithrombin

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Direct Thrombin Inhibitors

• Directly inhibit thrombin (factor IIa)

• Available as:

  • Intravenous

  • Oral agents

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Warfarin

• Oral anticoagulant

Mechanism

• Inhibits vitamin K epoxide reductase

• Reduces activation of:

  • Factor II

  • Factor VII

  • Factor IX

  • Factor X

Pharmacology

• Metabolized in the liver

• Half-life: ~40 hours

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Aspirin

• Antiplatelet agent

Mechanism

• Inhibits cyclooxygenase (COX)

• Reduces thromboxane A2

• Decreases platelet aggregation

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Reversal and Drug Considerations

Warfarin

• Metabolized in liver

• Use cautiously in liver disease

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Heparin & LMWH

• Reversed by protamine sulfate

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Fondaparinux & LMWH

• Renal excretion

• Avoid or use cautiously in renal failure

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Dabigatran

• Specific reversal agent available

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Tranexamic Acid

Clinical Use

• Widely used in orthopaedic procedures:

  • Joint replacement

  • Major fracture surgery

Benefits

• Reduces perioperative blood loss

• Supports clot stability

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Mechanism of Action

• Acts on the fibrinolytic pathway

• Inhibits conversion of:

  • Plasminogen —}   Plasmin

Effect

• Reduces fibrin breakdown

• Promotes stable clot formation

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Key Takeaways

• Orthopaedic patients are at high risk for DVT and PE

• Coagulation cascade involves extrinsic, intrinsic, and common pathways

• CTPA is the preferred imaging modality for PE

• Anticoagulants act at different levels:

  • Factor Xa

  • Thrombin

  • Platelets

• Drug selection depends on patient factors (renal function, bleeding risk)

• Tranexamic acid plays a key role in reducing surgical blood loss