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Investigations for PE and DVT, including sensitivity and specificity. + venous anatomy and V/Q mismatch

Investigations of DVT

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Investigations for PE and DVT, including sensitivity and specificity. + venous anatomy and V/Q mismatch. Investigations of DVT. Wells Criteria, for DVT . These clinical prediction rules are designed to increase the probability of an accurate diagnosis of deep venous thrombosis - PowerPoint PPT Presentation

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Investigatsions for PE and DVT, including sensitivity and specificity. + venous anatomy and V/Q mismatch

Investigations for PE and DVT, including sensitivity and specificity.

+ venous anatomy and V/Q mismatchInvestigations of DVT

Wells Criteria, for DVT These clinical prediction rules are designed to increase the probability of an accurate diagnosis of deep venous thrombosis

Active cancer (1 point) Paralysis, paresis, or recent plaster immobilisation of the lower extremities (1 point) Recently bedridden for 3 days or more, or major surgery within the previous 12 weeks requiring general or regional anaesthesia (1 point) Localised tenderness along in the distribution of the deep venous system (1 point) Entire leg swollen (1 point) Calf swelling at lease 3cm larger than that on the asymptomatic side (measured 10cm below tibial tuberosity) (1 point) Pitting oedema confined to the symptomatic leg (1 point) Collateral superficial veins (nonvaricose) (1 point) Previously documented DVT (1 point) Alternative diagnosis at least as likely as DVT (-2 points)

Score of 2 or higher = DVT likelyScore of less than 2 = DVT unlikelyKey Points on DVTClinical prediction rules (eg Wells Criteria) may be used to categorise patients into low, medium or high risk Low risk and negative serum D-Dimer effectively excludes DVT Medium and high risk patients should undergo doppler ultrasound without D-Dimer estimation Ultrasound is highly sensitive for proximal lower limb deep vein thrombosis (97%). Specificity also >95%.US is less sensitive for deep calf vein thrombosis (73%) and for iliac vein thrombosis After a negative doppler ultrasound, follow-up US in patients with high clinical suspicion may be indicated to exclude a calf thrombosis that is propagating proximally

US procedureEach venous segment is assessed for the presence of thrombosis, indicated by venous dilation and incompressibility during probe pressure (B-mode)Doppler findings suggestive of acute DVT are absence of spontaneous flow, loss of flow variation with respiration, and failure to increase flow velocity after distal augmentation.

DVT Differential DiagnosisLocalized muscle strain, contusion, or Achilles tendon rupture can often mimic the symptoms of DVT. Cellulitis may cause edema, localized pain, and erythema. Unilateral leg swelling can also result from lymphedema, obstruction of the popliteal vein by Baker cyst, or obstruction of the iliac vein by retroperitoneal mass or idiopathic fibrosis. Bilateral leg edema suggests heart, liver, or kidney failure or IVC obstruction by tumor or pregnancy.

The Virchow triad (stasis, vascular injury, and hypercoagulability) should be the cornerstone for assessment of risk factors for DVT. In most cases, the cause is multifactorial.

Investigations for PE

Investigation of PE in shock

Wells Criteria for PEPrior to imaging, one must clinically calculate the probability of PE.

- Clinical signs and symptoms of deep venous thrombosis (leg swelling and deep venous pain): 3 points. PE as or more likely than an alternative diagnosis: 3 points. Previously objectively diagnosed DVT or PE: 1.5 points. Active cancer (less than 6 months since therapy or palliative stage): 1 point. Recent Immobilisation: 1.5 points Bedrest for at least 3 consecutive days. Surgery in the previous 4 weeks. Heart rate greater than 100 per minute: 1.5 points. Haemoptysis: 1 point. Total Score: 0-1 = Low, 2-6 = Intermediate, 7+ = High probability

Key Points on PE investigationsThe role of a chest Xray in suspected Pulmonary Embolism (PE) is to exclude other causes that may mimic PE and to guide further investigations Although the CXR is abnormal in most patients with pulmonary embolization with infarction, the abnormalities are often nonspecific (e.g., atelectasis, pleural effusions, small infiltrates). The Westermark sign (dilated pulmonary vasculature proximal to embolus with oligemia distal) and Hampton's Hump (a pleural-based density with a rounded border facing the hilum) are specific though uncommon findings in pulmonary emboli.

D-DimersPatients who are at low probability for PE should have a D-Dimer. A negative D-Dimer in a low probability case of suspected PE rules out the diagnosis and no further investigation is indicated Patients with moderate to high pre-test probability of PE should have further imaging

Key Points on PE investigationsCT Pulmonary Angiography demonstrates PE by showing filling defects, within the contrast filled pulmonary arteries. Preferred in patient with chronic lung disease and abnormal CXR, as they already have V/Q mismatch.The Prospective Investigation of Pulmonary Embolism Diagnosis II (PIOPED II) trial reported a sensitivity of 83% and specificity of 96% Another study both >85

Ventilation/Perfusion Scans (V/Q) Lung perfusion images are taken after the intravenous injection of technetium-99m macroaggregated albumin. A PE characteristically appears as a pleural based segmental perfusion defect. 1 Any perfusion defects are compared to ventilation images (involves pt breathing in technetium labelled argon) and any regions of mismatch are considered suspect for PE Specific but not sensitive ie. negative test does not rule it out and need to preoceed to CTPA if clinical suspicion persist It is preferred in younger patients due to lower radiation dose and in patients with contraindicates for CT contrast CXR: There is a peripheral wedge shaped opacity representing pulmonary infarction and atelectasis secondary to a pulmonary embolus (arrow). This radiographic sign is referred to as Hampton's Hump.

Axial and reconstructed images of bilateral pulmonary arterial emboli (arrows)

Ventilation Perfusion Scan of Bilateral Embolism: The ventilation series demonstrates uniform distribution of tracer throughout both lung fields. The perfusion series demonstrates generalised reduced tracer uptake in the right lung with multiple segmental and subsegmental perfusion defects throughout both lung fields. These findings have a high probability for recent pulmonary embolism.

Other tests Arterial Blood GasesA clinically significant pulmonary embolism is almost always associated with hypoxemia (oxygen saturation