Key Facts

Venous thromboembolism encompasses deep vein thrombosis and pulmonary embolism. Hospital-associated thrombosis accounts for a significant proportion of preventable hospital deaths. Systematic risk assessment and appropriate prophylaxis are fundamental to safe surgical care.

Epidemiology

VTE affects approximately 1-2 per 1,000 of the UK population annually. Without prophylaxis, DVT rates reach 40-60% after major orthopaedic surgery and 15-30% after general surgery. PE is the direct cause of death in approximately 1-2% of all hospital inpatients.

Aetiology

Virchow's triad underpins VTE pathogenesis:

• Stasis: Immobility, bed rest, long-haul travel, venous obstruction
• Endothelial injury: Surgery, trauma, central venous catheters
• Hypercoagulability: Malignancy, inherited thrombophilia (Factor V Leiden, prothrombin gene mutation), OCP/HRT, pregnancy, antiphospholipid syndrome

Additional surgical risk factors: operative duration >90 minutes, pelvic/abdominal surgery, malignancy, obesity (BMI >30), age >60 years.

Pathophysiology

Venous thrombi typically originate in valve sinuses of deep leg veins where blood flow is slowest. The clot consists of a fibrin-rich red thrombus with entrapped red cells. Proximal propagation increases the risk of embolisation to the pulmonary vasculature. Thrombus formation is initiated by tissue factor exposure and propagated via the coagulation cascade, with inadequate natural anticoagulant regulation (protein C, protein S, antithrombin).

DVT

• Unilateral leg swelling, warmth, and erythema
• Calf tenderness, distended superficial veins
• Homan's sign (unreliable — calf pain on dorsiflexion)
• May be asymptomatic (especially post-operative)

Pulmonary Embolism

• Sudden-onset dyspnoea, pleuritic chest pain, haemoptysis
• Tachycardia, tachypnoea, hypoxia
• Massive PE: cardiovascular collapse, raised JVP, right heart strain

Post-Thrombotic Syndrome

• Chronic leg swelling, pain, skin changes (lipodermatosclerosis)
• Venous ulceration (typically above medial malleolus)

Red Flags

• Bilateral leg swelling with back pain — consider IVC obstruction (malignancy)
• Post-operative sudden cardiovascular collapse — consider massive PE
• Persistent unexplained tachycardia post-surgery — investigate for PE
• Phlegmasia cerulea dolens — massive iliofemoral DVT with limb ischaemia

Bedside

• VTE risk assessment: Department of Health tool — within 14 hours of admission
• Wells score for DVT: Score ≥2 = DVT likely → USS; <2 = unlikely → D-dimer
• Wells score for PE: Score >4 = PE likely → CTPA; ≤4 → D-dimer

Bloods

• D-dimer: High sensitivity, low specificity; age-adjusted cut-off (age × 10 µg/L if >50 years)
• FBC, coagulation screen: Baseline before anticoagulation
• Renal function: Adjust LMWH dose in renal impairment (eGFR <30)
• Thrombophilia screen: Only after acute event treated; not routinely recommended (NICE)

Imaging

• Compression USS: First-line for suspected DVT; sensitivity >95% for proximal DVT
• CTPA: Gold standard for PE diagnosis
• V/Q scan: Alternative if CTPA contraindicated (contrast allergy, renal impairment)
• Echocardiography: Assess right heart strain in massive PE

Special Tests

• Anti-Xa levels: Monitor LMWH in extremes of body weight, renal impairment, pregnancy
• HIT screen: Platelet count monitoring; PF4 antibodies if HIT suspected

Non-pharmacological

• Early mobilisation: The single most important non-pharmacological measure
• Anti-embolism stockings (AES): Thigh-length preferred; contraindicated in peripheral arterial disease (ABPI <0.8)
• Intermittent pneumatic compression (IPC): Recommended for all surgical patients where possible (NICE NG89)
• Adequate hydration: Avoid dehydration perioperatively

Pharmacological

• Standard prophylaxis: Enoxaparin 40mg SC OD (or dalteparin 5,000 units SC OD), started 6-12 hours post-operatively
• Renal impairment (eGFR <30): Unfractionated heparin 5,000 units SC BD/TDS
• Post-orthopaedic surgery: Rivaroxaban 10mg OD for 14 days (knee) or 35 days (hip) — or LMWH for same duration
• Cancer surgery: Extended prophylaxis 28 days with LMWH (ENOXACAN II trial)
• HIT: Fondaparinux 2.5mg SC OD as alternative
• Aspirin 75mg OD: Adjunct only in orthopaedic surgery (not sole prophylaxis)

Surgical/Interventional

• IVC filter: Consider in patients with confirmed proximal DVT and contraindication to anticoagulation
• Retrievable filters: Should be removed once anticoagulation can be safely started

Referral Criteria

• Confirmed VTE — haematology if recurrent or thrombophilia suspected
• HIT — urgent haematology input for alternative anticoagulation
• Massive PE — critical care and consideration of thrombolysis or embolectomy

• Appropriate VTE prophylaxis reduces DVT incidence by 60-70% and fatal PE by 50-65%
• Post-thrombotic syndrome develops in 20-50% of patients after proximal DVT within 2 years
• Mortality from untreated PE is approximately 30%; with treatment, mortality reduces to 2-8%
• Recurrent VTE occurs in approximately 5-10% within 1 year of completing anticoagulation
• Hospital-associated VTE accounts for approximately 50-60% of all VTE events

VTE Risk Factors (Surgical Patients)

LMWH Dosing by Indication

Key Trials