Venous Thromboembolism

Silent in up to half. Up to 50% of DVTs are asymptomatic, detected only on screening ultrasound, and clinical diagnosis is unreliable, with a sensitivity of 50-60% and a specificity of 50%.

Symptoms. Calf pain is the most common, felt in the posterior calf and often described as cramping or tightness. The leg swells, acutely or insidiously, and feels heavy or aching, and the pain is worse with standing or walking.

Signs on examination:

• Unilateral leg oedema - a difference of more than 3cm between the calves is significant
• Pitting oedema
• Calf tenderness on palpation
• Increased warmth, and erythema that may be subtle
• Superficial venous distension, with visible collateral veins
• Homans' sign (calf pain on forced dorsiflexion) - unreliable, only 50% sensitive

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Reading the Wells score. The total sets the pretest probability:

• 0 or less - low probability (5% DVT prevalence)
• 1-2 - moderate probability (17% DVT prevalence)
• 3 or more - high probability (53% DVT prevalence)

The differential of the painful, swollen postoperative leg:

The classic triad is rare. Dyspnoea, pleuritic chest pain and haemoptysis occur together in less than 20% of patients.

Symptoms by frequency:

• Dyspnoea (73%) - sudden onset, and may be present only on exertion at first
• Pleuritic chest pain (66%) - sharp, worse on inspiration
• Cough (37%)
• Leg pain or swelling (26%)
• Haemoptysis (13%)
• Syncope (9%) - suggests massive PE
• Anxiety or a sense of impending doom

Signs. Tachypnoea (respiratory rate over 20) is the most common sign. The others:

• Tachycardia (heart rate over 100)
• Hypoxia (SpO2 less than 95%)
• Low-grade fever, less than 38.5 degrees Celsius
• Elevated JVP
• Loud P2 (pulmonary hypertension)
• Right ventricular heave
• Hypotension (massive PE only)
• Cyanosis (a late sign)

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Severity. Haemodynamic stability, right ventricular dysfunction and troponin sort PE into four risk groups, and the group sets the treatment:

What it is. Post-thrombotic syndrome (PTS) is the chronic complication of DVT, a state of venous hypertension from valve incompetence and venous obstruction. It affects 20-50% of patients after a proximal DVT, in most cases within 2 years. The risk factors are proximal DVT, recurrent ipsilateral DVT, obesity, poor anticoagulation and inadequate compression.

How it develops. The acute thrombus damages the venous valves, and valve incompetence leads to reflux. Residual thrombus obstructs the vein, and the resulting venous hypertension causes oedema and skin changes.

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Clinical features. Leg pain and heaviness, worse on standing and better with elevation, chronic swelling, and skin changes (hyperpigmentation, eczema, lipodermatosclerosis). Venous ulceration marks the severe cases, 5-10%. Treatment is compression, elevation and wound care for ulcers.

Prevention. Adequate anticoagulation of the acute DVT reduces recurrence, and patients mobilise early once anticoagulated. Catheter-directed thrombolysis for iliofemoral DVT reduces PTS by 50%. Compression stockings for 2 years after the DVT are the contested measure:

D-dimer. Highly sensitive (95%) but poorly specific (50%): it is raised by surgery, trauma, pregnancy, cancer, infection and inflammation. A negative D-dimer reliably excludes DVT only in patients with a low pretest probability.

Compression ultrasound is the gold standard. Inability to fully compress the vein with probe pressure is diagnostic, and the scan also shows thrombus echogenicity and venous flow patterns. Sensitivity is 95% for proximal DVT and 70-80% for calf DVT, specificity 98%, and the test is non-invasive, radiation-free and available at the bedside.

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When to image. The threshold is low:

• Any clinical suspicion of DVT postoperatively
• Unexplained leg swelling, pain or warmth
• A diagnosed PE - to look for the DVT source

Other imaging options:

• CT venography - pelvic and IVC extension, or when ultrasound is non-diagnostic
• MR venography - an alternative for the pelvic veins, without radiation
• Contrast venography - the historical gold standard, rarely used now because it is invasive

Putting it together. Pretest probability decides whether D-dimer has any place:

Initial assessment includes:

• ABG - hypoxaemia, hypocapnia, respiratory alkalosis; may be normal in a small PE
• ECG - sinus tachycardia (most common), S1Q3T3 (classic but rare), right heart strain, new RBBB
• Chest X-ray - often normal; Westermark sign (oligaemia), Hampton hump (wedge infarct), pleural effusion

CTPA is the gold standard, with a sensitivity and specificity of 95-98%. It shows the thrombus in the pulmonary arteries and also any RV dilation, which is prognostic. It needs IV contrast, so it is contraindicated in severe renal impairment or contrast allergy.

V/Q scan is the alternative when CTPA is contraindicated, and works best in patients with a normal chest X-ray. Scans are reported as normal, low, intermediate or high probability. A high-probability scan with a high clinical probability is 96% diagnostic, but many scans come back intermediate, which does not help.

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Echocardiography assesses RV function at the bedside. RV dilation, hypokinesis, McConnell's sign and septal bowing are signs of strain, useful for risk stratification and for the thrombolysis decision, but echo is NOT diagnostic of PE because it cannot visualise the pulmonary arteries.

Biomarkers. Troponin rises with RV strain and BNP/NT-proBNP with RV dysfunction; both are prognostic, and a positive troponin carries a higher mortality.

Routine screening is not recommended. ACCP and AAOS do NOT recommend routine postoperative ultrasound screening. Most of the DVTs it detects are asymptomatic calf DVTs of low clinical significance, and screening has no proven mortality benefit. Some centres screen high-risk patients at 2 weeks, but the evidence does not support routine surveillance; the focus should be adequate prophylaxis.

Where it has a place. Beyond the symptomatic patient:

• Before major revision surgery, to rule out residual DVT
• Before stopping anticoagulation, to confirm resolution if indicated
• High-risk patients with a contraindication to chemical prophylaxis

The Caprini score is the most widely used tool for VTE risk stratification in surgical patients.

Reading the Caprini score. The total sets the intensity of prophylaxis:

• 0 - very low risk (0.5% VTE): early ambulation only
• 1-2 - low risk (1.5% VTE): mechanical prophylaxis
• 3-4 - moderate risk (3% VTE): mechanical plus chemical prophylaxis
• 5 or more - high risk (6% VTE): mechanical plus chemical plus extended prophylaxis (up to 35 days)

NICE. The UK National Institute for Health and Care Excellence provides the alternative risk assessment. Every orthopaedic inpatient needs a VTE risk assessment, and every patient undergoing THA, TKA or hip fracture surgery is automatically high risk. Bleeding risk must be assessed alongside it, and prophylaxis individualised.

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Why mechanical. It addresses the stasis limb of Virchow's triad and carries no bleeding risk, so it can be used when chemical prophylaxis is contraindicated. In high-risk patients it should be combined with chemical prophylaxis, not substituted for it.

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When not to compress. Compression is contraindicated in:

• Peripheral arterial disease (ABPI less than 0.8)
• Severe peripheral neuropathy
• Severe lower limb oedema from cardiac failure
• Skin conditions that prevent application
• Active DVT (compression may dislodge thrombus)

LMWH. Enoxaparin is the widely used agent: 40mg SC daily, or 30mg SC BD as the higher dose for very high risk, reduced to 30mg daily when the CrCl is 15-30 mL/min. It starts 12h before surgery in the European protocol or 12-24h after in the North American, and runs for a minimum of 10-14 days, extendable to up to 35 days after THA, TKA and hip fracture (see Timing and Duration).

DOACs. Rivaroxaban (Xarelto) 10mg PO daily, and apixaban (Eliquis) 2.5mg PO BD. Dabigatran (Pradaxa) is given as 110mg x 2 PO on day 1, then 220mg daily, and is not approved for prophylaxis in some jurisdictions.

Aspirin. 100-300mg PO daily, which the AAOS considers acceptable for VTE prophylaxis. ACCP 2012 lists aspirin as a Grade 1B option alongside LMWH, fondaparinux, the DOACs, low-dose heparin and adjusted-dose warfarin, all carrying the same 1B recommendation for a minimum of 10-14 days. The preference for LMWH over those alternatives is a separate and much weaker suggestion (Grade 2C/2B): aspirin is not a downgraded choice in that guideline, and saying so misrepresents it. It may be used for extended prophylaxis (days 10-35) after LMWH during the hospital stay: aspirin for the extended phase after perioperative anticoagulation is the position of the AAOS, and the design EPCAT II actually tested.

Warfarin. Target INR 2-3, with monitoring, interactions and a slow onset. It is less commonly used now that DOACs are available, but may be appropriate if the patient is already on warfarin for another indication.

Choosing the agent. LMWH suits all high-risk patients, especially if bleeding is a concern. Rivaroxaban suits patient preference and outpatient compliance, and apixaban, with the lowest bleeding, the elderly and moderate CKD (CrCl 25-50). Aspirin suits lower-risk patients or the extended phase.

When to start each agent:

How long. ACCP 2012 recommends prophylaxis for a minimum of 10-14 days (Grade 1B) and separately suggests extending it to up to 35 days (Grade 2B). The extension is widely practised after THA, TKA and hip fracture surgery, but it is the weaker of the two claims, and quoting "35 days, Grade 1B" merges them and overstates the evidence. VTE risk persists for 6-12 weeks after surgery, and 25% of VTEs occur after hospital discharge.

Warfarin. Stop it about 5 days before surgery and confirm the INR is below 1.5 on the day. Bridging with therapeutic LMWH is reserved for genuinely high thrombotic risk: a mechanical mitral valve, a VTE or stroke within about 3 months, or a very high CHA2DS2-VASc. For most atrial-fibrillation patients the BRIDGE trial showed that routine bridging increases bleeding without reducing thromboembolism, so moderate-risk AF is not bridged.

DOACs. Rivaroxaban, apixaban and dabigatran need no bridging, because of their short half-life. Stop them about 2 to 3 days before surgery: roughly 24 to 48 hours for normal renal function and a low-bleeding-risk procedure, longer for high-bleeding-risk surgery or renal impairment, especially dabigatran, which is renally cleared. Restart at prophylactic timing postoperatively, and resume the full treatment dose once surgical haemostasis is secure, commonly at 24 to 72 hours.

Reversal. For emergency surgery or major bleeding:

• Warfarin - intravenous vitamin K plus four-factor prothrombin complex concentrate (PCC); FFP only if PCC is unavailable
• Dabigatran - idarucizumab, a specific monoclonal antibody
• Rivaroxaban and apixaban (factor Xa inhibitors) - andexanet alfa where available, otherwise PCC

Absolute indications for a filter:

• Acute proximal DVT or PE with an absolute contraindication to anticoagulation
• Recurrent PE despite adequate anticoagulation
• Complications of anticoagulation requiring it to stop (major bleeding)

Relative indications, all controversial:

• Prophylactic filter in very high-risk trauma (controversial, not recommended routinely)
• Free-floating iliofemoral thrombus (some advocate, others anticoagulate)
• Massive PE with residual DVT, where further embolisation would be fatal
• Poor cardiopulmonary reserve, where any PE would be catastrophic

Filters are not indicated for:

• Routine prophylaxis in trauma or orthopaedic surgery
• As an alternative to anticoagulation when anticoagulation is feasible
• Calf DVT only

Retrievable filters are designed for temporary placement, less than 3-6 months (Celect, Denali, Gunther Tulip, OptEase). The retrieval rate in practice is disappointingly low, 20-40%.

Permanent filters are for a permanent contraindication to anticoagulation (Greenfield, Bird's Nest, Simon Nitinol). They are rarely placed now, because most contraindications are temporary.

Placement. Percutaneously via the femoral or jugular vein, under fluoroscopic or intravascular ultrasound guidance. The filter sits below the renal veins to protect renal venous drainage, or suprarenally if there is infrarenal IVC thrombosis or pelvic DVT.

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Complications of filters:

• Filter thrombosis (5-10%)
• Filter migration (3-5%)
• IVC perforation (rare)
• Filter fracture and embolisation
• Increased DVT risk distal to the filter
• Retrieval complications (stuck filters)

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