11. Thromboembolism, Thromboprophylaxis

I. Thromboembolism: Basic Concepts

Thrombosis

• Thrombosis: Formation of a blood clot inside a blood vessel during life
• Cause: Virchow's triad → Endothelial damage + blood-flow stasis + hypercoagulability
• Risk factors: Age, obesity, CV disease, pelvic/orthopedic surgery, immobility, long operation, malignancy

Types of Thrombosis

1. Arterial thrombosis: Platelet-rich clot → Stroke, myocardial infarction, acute limb/organ ischemia
2. Venous thrombosis: Stasis/hypercoagulability-related clot

• DVT: Deep vein thrombosis, most often lower limb/femoral-pelvic veins → Pulmonary embolism risk
• Portal vein thrombosis: Cirrhosis, pancreatitis, intra-abdominal infection/malignancy → Portal hypertension
• Budd-Chiari syndrome: Hepatic vein thrombosis → Abdominal pain, ascites, hepatomegaly
• Renal vein thrombosis: Flank pain, hematuria, renal dysfunction

Embolism

• Embolism: Vessel blockage by material that traveled from another part of the body
• Thromboembolism: Thrombus forms → Dislodges → Travels → Occludes another vessel
• Other emboli: Fat embolism, air embolism, septic embolism, amniotic fluid embolism

II. DVT and Pulmonary Embolism

Deep Vein Thrombosis

• DVT: Clot in deep veins, most commonly lower limbs
• Clinical features: Calf/leg pain, swelling, warmth, erythema, tenderness, superficial vein dilatation
• Homan's sign: Pain on dorsiflexion; unreliable, do not use alone
• Diagnosis: Duplex compression ultrasound first-line
• D-dimer: Sensitive but non-specific; useful mainly to exclude VTE in low-risk patients
• Venography: Historical gold standard, rarely used

Pulmonary Embolism

• PE: Blockage of pulmonary artery/branches, usually embolus from DVT
• Clinical features: Sudden dyspnea, chest pain, tachycardia, tachypnea, hypoxia, hemoptysis
• Severe PE: Syncope, hypotension, shock, cardiac arrest or sudden death
• Diagnosis: CT pulmonary angiography (CTPA) first-line in stable patients
• V/Q scan: Alternative if CTPA contraindicated
• ECG: Tachycardia common; S1Q3T3 possible but not sensitive
• Echocardiography: Right ventricular strain in massive/high-risk PE

III. Treatment

Anticoagulation

• Main treatment for DVT and stable PE if no contraindication
• Options: LMWH, UFH, fondaparinux, DOACs, warfarin
• Goal: Prevent clot extension, recurrence and fatal PE
• Balance benefit against bleeding risk

High-Risk PE and Contraindications

• Massive/high-risk PE: Hemodynamic instability, shock or cardiac arrest
• Treatment: Anticoagulation + systemic thrombolysis if bleeding risk acceptable
• Catheter-directed thrombolysis/thrombectomy or surgical embolectomy → Selected cases if thrombolysis contraindicated or fails
• IVC filter: Only if acute VTE and anticoagulation is contraindicated, or recurrent PE despite adequate anticoagulation

IV. Thromboprophylaxis

• Thromboprophylaxis: Measures to reduce VTE risk in high-risk patients
• Assess VTE risk + bleeding risk for every surgical patient
• Use mechanical prophylaxis if bleeding risk is high; add pharmacological prophylaxis when safe

Indications

• Major surgery, especially orthopedic, cancer, pelvic/abdominal surgery
• Trauma, spinal cord injury, ICU stay
• Immobile medical patients: Stroke, heart failure, severe infection/respiratory failure
• Previous/family history of VTE, known thrombophilia, active malignancy
• Long operation and postoperative immobility

Mechanical Prophylaxis

• Stimulate venous return → Prevent stasis
• Early mobilization
• Active/passive movement of extremities, ankle pump exercises
• Graduated elastic compression stockings
• Intermittent pneumatic compression (IPC)

Pharmacological Prophylaxis / Anticoagulants

• UFH: Binds antithrombin → Inhibits thrombin (FIIa) and FXa
• LMWH: Shorter heparin chains → Mainly inhibits FXa; common surgical prophylaxis
• Fondaparinux: Synthetic indirect FXa inhibitor; not LMWH
• Warfarin / coumarin: Vitamin K antagonist → Decreases FII, VII, IX, X; slow action, INR monitoring, food/drug interactions
• DOACs: Dabigatran inhibits FIIa; rivaroxaban, apixaban, edoxaban inhibit FXa

Timing and Duration

• Start when surgical hemostasis is secure and bleeding risk is acceptable
• General surgery: Until fully mobilized, often 7-10 days depending on risk
• Major orthopedic surgery: Extended prophylaxis, up to 35 days in hip/knee/hip-fracture surgery protocols
• Major abdominal/pelvic cancer surgery: Extended prophylaxis up to 4 weeks if bleeding risk is acceptable