Venous Thromboembolism

Major cause of perioperative and in-hospital morbidity and mortality. Perioperative VTE:

• Is the most preventable cause of death in inpatients
• May be responsible for up to 10% of hospital-related death

Epidemiology and Risk Factors

Epidemiology:

• May affect up to 25% of inpatients

Risk factors:

• Surgery
  Single most important risk factor, although varies with type of surgery.
• Immobility
• Hospitalisation
• Malignancy
• OCP use
  4-fold risk.
• Factor V Leiden
  7-fold risk.

Pathophysiology

Thrombi:

• Develop in regions of reduced flow:
  • Commonly around valve pockets
  • Due to venous stasis
    Two types of venous flow:
    • Continuous venous flow
      Laminar flow due to vis a tergo, and dependent on organ flow. May be impaired by venous outflow obstruction:
      • Positioning
      • Tissue oedema
    • Intermittent flow
      Due to muscular pump, and important in preventing stasis in valve pockets. Impaired by:
      • General anaesthesia
      • Bed rest
• Initially consist of ‘red clots’
  Predominantly RBCs and fibrin, and are key in clot formation.
  • White clot forms as platelet and leukocyte layers accumulate
    These components are key in clot propagation.

Valve function is dependent on normal endothelial function:

• Venous valves secrete:
  • Greater amounts of anti-coagulant factors
    Thrombomodulin, endothelial cell protein C receptor.
  • Lower amounts of procoagulant factors
    ul-VWF.

Aetiology

Clinical Manifestations

Diagnostic Approach and DDx

Investigations

Management

Prevention

• Multiple strategies exist
• Institutional guidelines will dictate practice
• Implementation of guidelines is usually poor

Methods include:

• Mechanical
  • Minimise non-pulsatile flow
    • Early ambulation after surgery
    • Regular foot and calf exercises
      At least every 2 hours.
  • Intermittent pneumatic compression devices
    • Cornerstone of prevention
      • Should be used for at least 18 hours/day whilst non-ambulant
      • Should be applied intraoperatively for high risk cases
      • Patient compliance is critical
    • More effective than stockings
    • May be as effective as pharmacological methods, without ↑ risk
    • Contraindications:
      • Presence of acute DVT
      • Severe peripheral vascular disease
      • Recent skin graft
      • Deformity
      • Pressure injury
      • Peripheral neuropathy
  • Graduated Compression Stockings
    Provide no benefit when used in addition to pharmacological prophylaxis.
    • May still be indicated in other settings
      e.g. Heart failure.
    • Should not be worn under intermittent pneumatic compressors
    • Should only be applied in high risk patients, with a contraindication to pharmacological prophylaxis, and pneumatic compressors are not available or contraindicated
  • Inferior vena caval filters
    Can be considered if pharmacological prophylaxis is contraindicated and there is either a:
    • Spinal cord injury
    • Major pelvic fracture
    • Known acute VTE
• Pharmacological
  Institution of pharmacological prophylaxis needs to be tailored to bleeding risk.
  • Aspirin
    • Anti-platelet effect limits clot propagation
    • Reduced bleeding and infectious complications compared with anticoagulants
      May not be additive with anticoagulants.
    • May be as effective as warfarin in LMWH
  • Enoxaparin
    • Favoured due to best efficacy/bleeding risk
    • Dosing:
      • Usual: 40mg SC daily
      • CrCl <30ml/min: 20mg daily
      • Weight <50kg: 20mg daily
      • Weight >130kg: 60mg daily or 40mg BD
        Consider seeking haematological advice.
  • UFH
    • Reasonable alternative to LMWH in patients with renal insufficiency
  • Fondaparinux
    • Reasonable alternative to LMWH and UFH in HITS
  • NOACs
    • Equivalent risk reduction to LMWH
    • Evidence in favour of use stronger in some orthopaedic populations
    • ↑ bleeding complications relative to LMWH

Risk Assessment

In general, surgery risk is proportional to the duration and extensiveness of the surgery, and period of post-operative immobilisation

Into high-risk and low-risk of clotting, by inpatient type:

• Medical patient
  High risk
  • Age > 60
  • Ischaemic CVA
  • Previous VTE
  • Active malignancy
  • Decompensated CCF
  • Acute-on-chronic lung disease
  • Acute inflammatory disease
  • Acute neurological disease
  • Sepsis
  • Obesity
  • Varicose veins
  • OCP use
• Surgical patient
  • Major trauma
    • Multitrauma
    • TBI
    • Truncal trauma
    • Spine fracture or SCI
    • Long bone fracture
  • Malignancy
  • Major abdominal surgery
  • Laparascopic major abdominal surgery with one other risk factor

Anaesthetic Considerations

Marginal and Ineffective Therapies

Prevention:

Complications

Prognosis

Key Studies

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References

1. Gordon RJ, Lombard FW. Perioperative Venous Thromboembolism: A Review. Anesthesia & Analgesia. 2017 Aug;125(2):403–12.