Deep Venous Thrombosis Flashcards
Describe the venous anatomy of the legs
What is a DVT?
Deep vein thrombosis (DVT) is the development of a blood clot in a major deep vein in the leg, thigh, pelvis, or abdomen, which may result in impaired venous blood flow and consequent leg swelling and pain. DVT may also occur in the upper extremities or the brain.
Venous thromboembolism (VTE) includes DVT and pulmonary embolism.
What is the aetiology of thrombus formation?
Virchow’s triad:
- Alterations in blood flow - stasis in veins or turbulence in arteries
- Vessel wall damage
- Hypercoagulability
What are risk factors for DVT?
- previous DVT or PE
- major surgery (esp abdo or orthopaedic)
- immobility
- pregnancy/post-partum/COCP/HRT
- trauma
- malignancy
- hereditary thrombophilia syndrome (eg. protein C/S def, vWf)
- antiphospholipid antibody syndrome
- recent long-distance air travel
- increasing age
- obesity
What are the symptoms of DVT?
- localised pain along deep venous system
- calf swelling
What are the signs of DVT?
- pyrexia
- warm leg
- piting oedema
- unilateral calf swelling
- calf tenderness/erythema
- superficial venous distension
- Homan’s sign -> forced foot dorsiflexion causes increased pain in posterior calf BUT risk of dislodging thrombus
- Pratt’s sign -> squeezing posterior calf causes pain
What are differential diagnoses for (unilateral) leg swelling?
- vascular -> DVT, vasculitis, obstruction, vascular abnormalities
- infection -> cellulitis (can be cause + consequence of DVT)
- trauma
- inflammatory -> arthritis
- ruptured Baker’s cyst
If bilateral, consider cardiac, hepatic or renal failure, medications or pelvic venous congestion (?tumour)
Wells’ criteria are the most widely accepted algorithm used in the clinical diagnosis of DVT.
What is the Wells’ criteria for DVT diagnosis?
- Score ≥2.0 — High (probability ~40%)
- Score <2.0 — Low (probability ~15%)
What investigations are done next, given a DVT is ‘unlikely’ (Wells’ 1 point or less)?
- perform a D-dimer test and if it is positive, arrange:
- a proximal leg vein ultrasound scan within 4 hours
- if a proximal leg vein ultrasound cannot be carried out within 4 hours, LMWH should be administered whilst waiting for the proximal leg vein ultrasound scan (which should be performed within 24hrs)
If low pretest Wells score probability and negative D-dimer test -> exclude DVT
What investigations are done next, given a DVT is ‘likely’ (Wells’ 2 points or more)?
- a proximal leg vein ultrasound scan should be carried out within 4 hours and, if the result is negative, a D-dimer test
- if a proximal leg vein ultrasound scan cannot be carried out within 4 hours a D-dimer test should be performed and low-molecular weight heparin administered whilst waiting for the proximal leg vein ultrasound scan (which should be performed within 24 hours)
What is the use/purpose of a venous duplex ultrasound scan?
- asesses venous flow by use of doppler + vein compression
- first-line test in all high-probability pts (Wells’ 2+) or in low-probability pts (Wells <2) w/ an elevated D-dimer level to assess popliteal, deep femoral, femoral and common femoral veins
- high sensitivity + specficity (95%+)
- Venous ultrasound has a high sensitivity because: 1) deep veins in the lower extremities are easily visualised; 2) it scans multiple areas, making it likely that at least a portion of a clot is detected; and 3) compression readily identifies intravascular thrombus. Non-compressibility is the only sign prospectively validated with a high positive predictive value when compared with venography.
- In high-probability patients, a repeat ultrasound is indicated in 1 week if the initial ultrasound test is normal
- In low-probability patients, a repeat ultrasound is indicated in 1 week if D-dimer level is elevated and initial ultrasound is normal
What other blood tests can be done to aid diagnosis of DVT?
- INR and aPTT (required before starting IV heparin for baseline)
- urea + creatinine (to check for renal impairment)
- LFTs (may detect abnormalities associated w/ underlining provking factor eg cancer)
-
FBC (baseline + detect haem malignancy)
- high platelets -> essential thrombocytosis or myeloproliferative disorder
The main aim of therapy is to prevent PE. What is the treatment of DVT?
- do coagulation screen + platelet count - exclude pre-existing thrombotic condition
- first-line → apixaban or rivaroxaban (now instead of LMWH when DVT suspected)
- if neither apixaban or rivaroxaban are suitable then either LMWH followed by dabigatran or edoxaban OR LMWH followed by a vitamin K antagonist (VKA, i.e. warfarin)
Below, if using heparin: - check APPT (degree of coag) daily 4-6hrs after every dose of heparin -> maintain APPT of 1.5-2.5
- start 5-10mg warfarin (oral) at same time as heparin -> as warfarin is pro-thrombotic for first 48 hours -> must maintain INR at 2-3
- heparin + warfarin for at least 5 days until INR is in therapeutic range
- stop heparin when INR is 2-3
- treat for 3 months if post-op/6 months if no cause found/lifelong in recurrent DVT
see table for durations of warfarin
What lifestyle advice should be given to patients taking warfarin?
- medications - pts taking warfarin should consult the healthcare provided before starting any new drugs (OTC, prescription or herbal). Common meds that affect warfarin are antibiotics, anti-inflammatory agents, vitamins (vit K), ginseng, ginger and St John’s Wort
- alcohol - pts on warfarin should avoid drinking, limiting consumption to 1-2 servings of alcohol occasionally. Alcohol has antiplatelet effects and increases risk of the severe bleeding, even if INR remains in the target range
- foods - certain foods interfere w/ the effectiveness of warfarin, particularly those high in vitamin K (liver, broccoli, sprouts and green leafy vegetables). Large changes in diet should be avoided. Grapefruit and cranberry juice can also interact w/ warfarin
What is INR?
- international normalised ratio
- INR = (PTtest/PTnormal)ISI
- it is the ratio of a pt’s prothrombin time to a normal (control) sample, raised to the power of the ISI value for the analytical system used
- normal INR range for a healthy person is 0.9-1.3, and for people on warfarin therapy 2.0-3.0
- if the INR is high -> risk of bleeding
- if the INR is low -> risk of clotting
