Perioperative Pulmonary Embolism

1. Pathophysiology and Virchow's Triad in Surgery

• Venous stasis - immobility, positioning on the operating table, general anaesthesia reducing venous tone
• Hypercoagulability - the systemic inflammatory and prothrombotic response to surgical trauma, increases in coagulation factors (V, VIII, X, von Willebrand factor)
• Endothelial injury - direct vessel trauma, especially in pelvic, orthopaedic, and vascular surgery

• Increased right ventricular afterload → RV dilation and dysfunction
• Ventilation-perfusion mismatch → hypoxaemia
• Release of vasoactive mediators (serotonin, thromboxane A2) causing bronchoconstriction
• Reduced left ventricular preload → hypotension and shock

2. Risk Factors

• Factor V Leiden, Prothrombin G20210A, antithrombin deficiency, protein C and S deficiency, factor XI elevation

• Hip and knee arthroplasty (disproportionately elevated risk)
• Major abdominal and pelvic surgery (colorectal, gynaecological, urological)
• Neurosurgery and spinal surgery
• Operations involving renal cell carcinoma with IVC extension

3. Preoperative Risk Stratification

• Caprini Score and Rogers Score - these take into account the number of VTE risk factors and recommend prophylactic anticoagulation for moderate-to-high risk patients. Orthopaedic patients are excluded from general risk scores due to their disproportionately elevated VTE risk and are managed separately.
• The 9th edition ACCP Guidelines for Prevention of VTE in Non-Orthopaedic Surgical Patients recognise both scores and provide risk-stratified prophylaxis recommendations.

4. Prophylaxis

• Graduated compression stockings
• Pneumatic sequential compression devices (applied to the lower limbs intraoperatively and postoperatively)

• Low-molecular-weight heparin (LMWH) - e.g., enoxaparin
• Unfractionated heparin (UFH) - low dose subcutaneous
• Direct oral anticoagulants (DOACs) - particularly for orthopaedic surgery (rivaroxaban, apixaban, dabigatran)
• Low-dose aspirin - the Pulmonary Embolism Prevention (PEP) trial showed benefit in orthopaedic surgery

• Standard: duration of hospital stay
• Extended prophylaxis (>3 weeks post-surgery) is necessary for major procedures such as hip/knee arthroplasty, major abdominal/pelvic surgery for cancer, and surgery for IBD (LMWH for up to 28 days after any abdominal procedure for IBD - Bailey & Love, 28e)

• If the acute PE occurred >1 year earlier, the risk from temporarily stopping anticoagulation is probably small - Morgan & Mikhail's Clinical Anaesthesiology, 7e
• Emphasis is on preventing new embolic events with adequate perioperative prophylaxis

5. Intraoperative PE

• Sudden cardiovascular collapse, severe hypotension
• Hypoxaemia (unexplained fall in SpO₂)
• Bronchospasm
• Sudden decrease in end-tidal CO₂ (increased dead space - not specific but suggestive)
• Elevated central venous pressure (on invasive monitoring)
• TEE: right heart dilatation and dysfunction (may not directly visualise the clot)

• Intravenous fluids and vasopressors/inotropes (supportive care)
• Aspiration of air via central venous catheter if air embolism is suspected
• Cardiopulmonary bypass for emergency pulmonary embolectomy in extreme cases
• Postoperative consideration of IVC filter placement

6. Postoperative PE: Clinical Presentation

• Dyspnoea - most common (75-80% of cases); may be absent in ~25%
• Chest pain - second most common; may be pleuritic (worsened by inspiration) - only present in 20%; suggests peripheral infarction
• Haemoptysis - with pulmonary infarction
• Unilateral leg swelling (DVT symptoms) - <30% of PE patients
• Palpitations, syncope, severe anxiety
• Low-grade fever (<38.6°C; higher temperature suggests infection rather than infarction)
• Shock index >1 (HR > systolic BP) with impending arrest

7. Diagnosis

Clinical Probability Assessment

• Wells Score (PE version) and Revised Geneva Score - stratify patients into low, intermediate, and high pre-test probability (PTP)
• PERC Rule (Pulmonary Embolism Rule-Out Criteria) - if ALL 8 criteria met in a low-PTP patient, PE can be excluded without further testing - Rosen's:

D-Dimer

• 95-98% sensitive, 40-55% specific - Rosen's
• Useful to exclude PE in non-high PTP patients (NPV 99-100% with normal result)
• Age-adjusted threshold: Age × 10 ng/mL (when standard threshold is 500 ng/mL) - increases the number who can avoid CT by 5-6% overall and 10-20% in patients >70 years old
• False negatives: subacute/chronic PE, severe lipaemia, ongoing warfarin therapy
• Important caveat in postoperative patients: D-dimer is almost universally elevated after surgery due to wound healing - it has essentially no diagnostic utility in the early postoperative period and imaging is required when suspicion exists

Imaging

• CT Pulmonary Angiography (CTPA) - first-line recommended imaging when PE is suspected - Miller's Anesthesia, 10e
• V/Q scan - used when CTPA is contraindicated (contrast allergy, renal insufficiency, pregnancy - halving the perfusion dose is standard in pregnancy)
• Echocardiography - NOT recommended in initial diagnostic evaluation, but has utility in risk stratification, prognostication, and monitoring response to therapy once diagnosis is established - Miller's Anesthesia, 10e

Biomarkers

• Troponin - elevation indicates myocardial injury from RV strain; associated with high short-term mortality - Murray & Nadel, 2e
• BNP/NT-proBNP - marker of RV pressure overload
• ABG - hypoxaemia, hypocapnia (hyperventilation), respiratory alkalosis; increased alveolar-arterial oxygen gradient

8. Risk Stratification and Treatment

Classification - Miller's Anesthesia, 10e:

Treatment Table - Rosen's Emergency Medicine, 10e:

Anticoagulation

• Unfractionated heparin (IV infusion) - preferred when thrombolysis or surgical embolectomy is planned (short half-life, reversible)
• LMWH (e.g., enoxaparin) - for stable patients; predictable pharmacokinetics; avoid or dose-adjust in renal failure
• DOACs (rivaroxaban, apixaban, dabigatran) - preferred for low/intermediate risk if no contraindications; avoid in haemodynamic instability

Respiratory and Haemodynamic Support - Rosen's:

• Supplemental oxygen to target SpO₂ >90% (hypoxaemia worsens pulmonary vasoconstriction)
• Avoid intubation if possible - positive pressure ventilation increases intrathoracic pressure, reduces RV preload, and can precipitate haemodynamic collapse in severe PE
• If intubation is unavoidable: pre-optimise haemodynamics with vasopressors before induction
• Vasopressors (noradrenaline) + inotropes (dobutamine) for RV support

Systemic Thrombolysis

• Alteplase (rtPA) 100 mg IV over 2 hours - indicated for massive PE without contraindications
• Relatively contraindicated in recent surgery - the perioperative period itself is a relative contraindication; the risk of haemorrhage must be weighed against the risk of death from massive PE
• Catheter-directed thrombolysis delivers lower doses locally for intermediate-high risk PE with unacceptable bleeding risk

Surgical / Interventional Options

• Catheter-directed thrombectomy - mechanical clot disruption/aspiration
• Surgical pulmonary embolectomy - reserved for massive PE with contraindications to thrombolysis or failed thrombolysis; patients are critically ill and often haemodynamically unstable; cardiopulmonary bypass is required - Morgan & Mikhail, 7e
• IVC filter - placed percutaneously under local anaesthesia + sedation; indicated when anticoagulation is contraindicated (recent surgery with high bleeding risk) or has failed; protects against further embolization but does NOT treat the existing PE and may increase long-term DVT risk

9. Special Situations

Pregnancy

• Leading cause of maternal mortality (15% of maternal deaths, USA 2003-2011) - Murray & Nadel, 2e
• Risk ~5x higher than non-pregnant women due to raised coagulation factors (V, VIII, X, von Willebrand factor), fall in protein S, and venous stasis from IVC compression
• Peak incidence: postpartum, especially after caesarean section
• D-dimer is not reliable in pregnancy - the pregnancy-adapted YEARS algorithm (clinical signs of DVT + haemoptysis + PE as most likely diagnosis + D-dimer) can assist but has limitations
• Imaging: V/Q scan (halved perfusion dose) or CTPA, both acceptable with radiation modifications
• Treatment: LMWH throughout pregnancy; warfarin teratogenic; DOACs contraindicated

IBD Surgery

• IBD carries 3x increased VTE risk; postoperative VTE rate ~3% - Bailey & Love, 28e
• 74% of VTE events occur during initial hospitalisation, 61% within first 2 weeks
• Extended prophylaxis with LMWH for up to 28 days post-surgery recommended

10. Summary: Key Perioperative Considerations

• Miller's Anesthesia, 2-Volume Set, 10e - Perioperative PE classification, imaging, risk stratification
• Morgan & Mikhail's Clinical Anaesthesiology, 7e - Intraoperative PE, anaesthetic management
• Rosen's Emergency Medicine, 10e - Clinical features, diagnosis (PERC, D-dimer, CTPA), risk stratification and treatment table
• Schwartz's Principles of Surgery, 11e - Risk factors, Caprini/Rogers scoring, prophylaxis guidelines
• Murray & Nadel's Respiratory Medicine, 2e - Troponin prognostication, PE in pregnancy
• Current Surgical Therapy, 14e - VTE prophylaxis within ERAS; mechanical + pharmacological strategies
• Bailey & Love's Short Practice of Surgery, 28e - Extended prophylaxis in IBD surgery