- Venous thrombosis is significant cause of morbidity and mortality
- Pulmonary embolus accounts for 10 - 25 % of hospital deaths
- At least 20% patients with a DVT develop a post-thrombotic limb
- Most calf DVTs are clinically silent
- 80% of calf DVTs lyse spontaneously without treatment
- 20% of calf DVTs propagate to the thigh and have increased risk of PE
- Thrombus formation and propagation depends on the presence of Virchow's triad
- Venous stasis
- Hypercoagulable state
- Endothelial damage
- Immobility contributes to venous stasis
- Endothelial damage can result from external compression
- A hypercoagulable state can be due to drugs or malignancy
Risk factors for venous thrombosis
||Disease or surgical procedure
||Trauma or surgery esp. pelvis, hip, lower limb
||Recent myocardial infarction
||Lower limb paralysis
|High-dose oestrogen therapy
||Inflammatory bowel disease
|Previous DVT or PE
|Antithrombin III deficiency
|Protein C deficiency
||Paroxysmal nocturnal haemoglobinuria
|Protein S deficiency
- It is estimated that about 1:250 of the population have a congenital thrombophilia
- Potential for venous thrombosis can be investigated by a thrombophilia screen
- FBC and blood film
- >Clotting studies - APPT / PT / TT
- Reptilase test
- Protein C & S and Antithrombin III assay
- Lupus anticoagulant
Epidemiology of DVT and pulmonary embolus
|Low risk group
|Moderate risk group
|High risk group
Risk of venous thrombosis during surgery
- Low risk
- Minor surgery (<30 min) + no risk factors other than age
- Major surgery (> 30 min) , age <40 yrs + no other risk factors
- Minor trauma or medical illness
- Moderate risk
- Major general, urological, gynaecological, cardiothoracic, vascular or neurological surgery + age
>40 yrs or other risk factor
- Major medical illness or malignancy
- Major trauma or burn
- Minor surgery, trauma or illness in patients with previous DVT, PE or thrombophilia
- High risk
- Fracture or major orthopaedic surgery of pelvis, hip or lower limb
- Major pelvic or abdominal surgery for cancer
- Major surgery, trauma or illness in patient with previous DVT, PE or thrombophilia
- Major lower limb amputation
Prevention of thromboembolism
Prevention of stasis
- Early mobilisation
- Graduate compression stockings
- Intermittent pneumatic compression (e.g. Flowtron boots)
Pharmacologically reduce hypercoagulable state
- Acidic mucopolysaccharide
- Unfractionated heparin (MW = 15 kDa)
- Low Molecular Weight Heparin (MW = 5 kDa)
- Both potentiate Antithrombin III by inactivating activated clotting factors
- Unfractionated heparin anti-Xa activity = anti IIa activity
- Low Molecular Weight Heparin anti-Xa activity 4x > than anti IIa activity
- Does not have significant effect on APPT
- Side effects of unfractionated Heparin
- Idiosyncratic thrombocytopenia
- Coumarin derivative & vitamin K antagonist
- Inhibits vitamin K dependent post translational carboxylation of factors II, VII, IX & X
- Graduated compression stockings reduce incidence of DVT by 50%
- No proven benefit of thigh-length compared to calf-length stockings
- Unfractionated and low molecular weight heparin are equally effective
- Reduce DVTs by 70% and PEs by 50%
- Unfractionated heparin usually given 5000u 3x daily
- Low Molecular Weight Heparin - Enoxaparin 20 or 40 mg daily
- New drugs useful in DVT prophylaxis include
- Thrombin inhibitors (e.g. hirudin)
- Specific factor Xa inhibitors (e.g. fondaparinux)
- Factor Xa inhibitors may be more effective than LMWH
Current recommendations for DVT prophylaxis
- All hospital inpatients
- Should be assessed for clinical risk factors and overall risk of thromboembolism
- Should receive prophylaxis according to degree of risk
- Prophylaxis should continue until discharge
- Low risk patients should be mobilised early
- Moderate risk patients should receive specific prophylaxis
Clinical features of DVT
- Clinical presentation of a DVT can be very non-specific
- Many are asymptomatic
- Clinical features depends on site of venous occlusion
- Classical clinical features of a calf DVT are:
- Calf pain and tenderness
- Persistent tachycardia
- Homan's sign = pain on passive dorsiflexion of the ankle is a non-specific sign
- Occlusion of the ileofemoral vein can result in venous gangrene (phlegmasia cerulea dolens)
Picture provided by Chris Malkin, Leeds General Infirmary, Leeds, United kingdom
Investigation of suspected DVT
- Less than 50% of those suspected of having DVT have clot identified on imaging
- A fibrin degradation product that can be assayed in plasma
- Levels raised in the presence of recent thrombus
- A negative result almost excludes the presence of venous thrombosis
- Decision to proceed to venography or ultrasound often based on D-dimer result
- Gold standard
- Will identify both calf vein and proximal thrombus
- Painful and time consuming investigation.
- 2-3% of patients develop contrast reaction
- Technique has three components - all operator dependent.
- Venous compressibility
- Detection of Doppler flow
- Visualisation of clot
- In femoro-popliteal segment - sensitivity = 94%. specificity = 100%
- In calf veins - sensitivity = 73%. specificity = 86%
- Able to exclude femoro-popliteal or major calf DVT in symptomatic patients
Treatment of venous thrombosis
- Aims of treatment:
- Prevention of pulmonary embolus
- Restore venous and valvular function to prevent the post thrombotic limb
- Few aspects of treatment submitted to RCTs
- Main component of treatment
- Initially with unfractionated or low molecular weight heparin
- Followed by oral anticoagulation
- LMWHs have increased bioavailability and linear kinetics
- The treatment of isolated calf DVTs is of unproven benefit
- Optimal duration of treatment unknown
- No proof that treatment beyond 3-6 months is required
- Considered in massive ileo-femoral thrombosis associated with phlegmasia cerulea dolens
- Good early results with 62% complete and 38% partial clearance of ileo-femoral segment
- Unfortunately re-occlusion common
- Thrombolysis of unproven benefit
- Accounts for 3% of hospital inpatients deaths
- Untreated has a mortality of 30%
- Treated mortality reduced to about 2%
- Only 10% have clinical signs of a DVT
||Low grade pyrexia
|Pleuritic chest pain
||Neck vein distension
||Increased pulmonary second sound
Investigations of possible pulmonary embolus
- Arterial blood gases - hypoxia, hypocarbia but may be normal
- ECG - Signs of right heart strain - classically S1Q3T3
- CXR - Show oligaemia and central pulmonary markings and excludes other pathologies
- Ventilation / Perfusion scanning - May confirm or refute diagnosis
- Pulmonary angiography and echocardiography useful if haemodynamic instability
- Spiral CT might replace pulmonary angiography
- Lower limb investigations for DVT as above
Management of pulmonary embolus
- Depends on degree of suspicion and haemodynamic stability
- If high degree of suspicion but stable:
- Anti-coagulate with heparin or LMWH
- Oxygen, analgesia, colloid to increase CVP
- Warfarinise for at least 3 months
- If haemodynamically unstable:
- Consider pulmonary thrombolysis via pulmonary artery catheter
- If thrombolysis contraindicated consider pulmonary embolectomy
Inferior vena caval filters
- Inserted percutaneously usually via femoral vein
- Present a physical barrier to emboli
- Indicated if:
- Recurrent pulmonary emboli despite adequate anti-coagulation
- Extensive proximal venous thrombosis and anticoagulation is contraindicated
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