pulmonary%20thromboembolism
PULMONARY THROMBOEMBOLISM
Pulmonary embolism is the blockage of the blood vessels in the lungs usually due to blood clots from the veins, especially the veins in the legs and pelvis.
Dyspnea, chest pain, syncope or tachypnea (respiratory rate of ≥20/min) occur in most cases of pulmonary embolism.
Pleuritic chest pain with or without dyspnea is one of the most frequent presentations of this disease.
Syncope or shock are the hallmark signs of central pulmonary embolism and usually result in severe hemodynamic repercussions.
Signs of hemodynamic compromise and reduced heart flow are also usually present.

Diagnosis

  • Clinically unstable patients may have massive pulmonary embolism (PE)
  • Thrombolytic therapy should be considered

Assessment

Clinical Probability

  • Evaluating the likelihood of pulmonary embolism (PE) in an individual patient according to the clinical presentation is of utmost importance in the interpretation of diagnostic test results & the selection of an appropriate diagnostic strategy
  • A reasonable clinical suspicion is required to avoid missing the diagnosis of PE
  • Clinical evaluation allows patients to be classified into probability categories corresponding to an increasing prevalence of PE
  • Clinical probability may be estimated implicitly by clinical judgment or explicitly by a validated prediction rule
  • All patients w/ possible PE should have clinical probability assessed & documented
  • Patients should also be evaluated for risk factors for venous thromboembolism (VTE)

Prediction Rule vs Clinical Judgment

  • To identify a patient w/ a high likelihood of PE, prediction rules appear to be more accurate than clinical judgment
  • Clinical judgment is accurate to discern whether patient is of low likelihood of PE
    • Patients that have low clinical probability of PE, no lower limb deep vein thrombosis (DVT) & nondiagnostic lung scan have low risk of PE

Estimation of Pretest Probability of PE

  • Methods: Wells, Wicki, Kline, revised Geneva score
    • Wells method is the most frequently used clinical prediction rule
  • In any of the methods used, the proportion of patients w/ PE is around 10% in the category of low probability, 30% in moderate probability, & 65% in high probability
  • Clinical evaluation allows patients to be classified into probability categories corresponding to an increasing prevalence of PE

Wells (Canada) Method

  • Requires that the patient have clinical features suggestive of PE (eg breathlessness, &/or tachypnea w/ or w/o pleuritic chest pain, &/or hemoptysis)
  • Along w/ 2 other features:
    • The absence of another reasonable clinical explanation
    • The presence of a major risk factor
  • If both are true then the probability is high
  • If only one of the above is true then the probability is intermediate
  • If neither is true then the probability is low
Modified Wells Pre-Test Probability Scoring System
 Variable  Points  Pretest probability  Total points
 Clinical signs & symptoms of DVT  = 3.0  Based on likelihood of PE  
 Alternative diagnosis is less likely than PE  = 3.0  PE less likely  ≤4
 HR >100 beats/min  = 1.5  PE likely  >4
 Immobilization or surgery in the last 4 days  = 1.5  According to risk groups  
 Previous DVT/PE  = 1.5  High  >6
 Hemoptysis  = 1.0  Intermediate  5-6
 Malignancy (w/ treatment w/in the last 6 months or palliative)  = 1.0  Low  ≤4
Modified from: Institute for Clinical Systems Improvement. Health care guideline: venous thromboembolism diagnosis and treatment. 13th ed. Jan 2013.

Pulmonary Embolism Rule-Out Criteria (PERC)

  • Helps exclude patients at very low risk for PE
  • Studies show that PERC validation done prior to D-dimer testing is 100% sensitive
  • Presence of any of the following indicates a positive PERC
    • Age > 49 years old
    • Pulse rate >99 bpm
    • Pulse oximetry <95% at room air
    • Hemoptysis
    • Patient on exogenous Estrogen therapy
    • Clinical history of venous thromboembolism
    • Previously intubated due to surgery or trauma or hospitalization w/in the last 4 weeks
    • Unilateral leg (calf) swelling

Massive PE

  • In patients who are too unstable for lung imaging, right ventricle (RV) dysfunction can usually be found at the bedside
    • Left parasternal heave, distended jugular veins & systolic murmur of tricuspid regurgitations that increases w/ inspiration
    • ECG may show new right bundle branch block, RV failure, or other evidence of RV strain (eg inverted T waves in leads V1-V4)
  • The most useful initial test is echocardiography which is able to show indirect signs of acute pulmonary hypertension & RV overload if acute PE is the cause of hemodynamic compromise
  • When patient has already been stabilized by supportive treatment, definite diagnosis should be determined
  • CT pulmonary angiography may be used to confirm diagnosis (≥50% decreased perfusion)

Laboratory Tests

  • First-line diagnostic tests such as electrocardiography (ECG), chest X-ray (CXR) & arterial blood gases (ABG) are indicated to assess clinical probability of PE & general condition of patient
  • Laboratory results can be normal but some abnormal findings increase the suspicion for PE

Arterial Blood Gas (ABG)

  • Can show hypoxemia, hypocapnia, & widened (A-a) O2 difference

Chest X-ray (CXR)

  • May demonstrate atelectasis, pleural-based infiltrates or effusions, or engorged central pulmonary artery associated w/ a paucity of peripheral vessels

Electrocardiogram  ECG)

  • Can show right axis deviation, supraventricular arrhythmia, S1Q3T3 pattern or P-pulmonale

B-type Natriuretic Peptide (BNP) & Troponin

  • Consider in a patient w/ substantial clot burden, abnormal echocardiogram, or clinical findings suggestive of PE
  • Elevated BNP & troponin are associated w/ RV strain & increased mortality even in the absence of hemodynamic instability, especially if considering massive PE

D-Dimer

  • D-dimer is a highly sensitive but a nonspecific screening test for the presence of PE
    • Sensitivity may be decreased if the duration of VTE manifestations is >2-3 days prior to testing, if the patient is on Heparin therapy, &/or w/ history of recent surgical procedure or trauma
    • Best used for evaluation of outpatients in the emergency department
  • Recommended confirmatory test for patients w/ low pretest probability & positive for PERC
  • A negative D-dimer test via any D-dimer method (simpliRed, Vidas or MDA) reliably excludes PE in patients w/ low clinical probability; such patients do not require imaging for VTE
  • A negative D-dimer test using ELISA (Vidas) reliably excludes PE in patients w/ intermediate probability
  • A positive D-dimer requires further evaluation to exclude PE adequately
    • However, raised levels of D-dimer does not confirm the presence of VTE because such levels are found in hospitalized patients, obstetrics, peripheral vascular disease, cancer & many inflammatory diseases as well as increasing age
  • CV D-dimer should not be performed in those w/ high clinical probability of PE
    • Computed tomographic pulmonary angiography (CTPA) is recommended as initial test for these cases; if not available, or if patient is unstable or has contraindications, bedside echocardiography is recommended
  • D-dimer is inappropriate for suspected VTE w/ recent surgery or trauma
    • These patients should proceed directly to radiologic studies (eg duplex US or CTPA)

Imaging

Echocardiography

  • Most useful initial test which typically shows indirect signs of acute pulmonary hypertension & RV overload if acute PE is the cause of hemodynamic changes
  • If patient is unstable, thrombolytic treatment or surgery can be done based only on compatible echocardiography findings
  • If patient has been stabilized, a definitive diagnosis should be pursued
    • Both lung scan, spiral computed tomography (sCT) & bedside transesophageal echocardiography (TEE) are usually able to confirm diagnosis
    • Normal lung scan or sCT angiogram suggests that another cause of shock should be found

Computed Tomographic Pulmonary Angiography (CTPA)

  • CTPA is recommended as the initial lung imaging modality for non-massive PE
  • Increasingly used as an adjunct or alternative to other imaging modalities & is superior in specificity to isotope lung scanning
  • Enables direct visualization of the pulmonary emboli & may provide information about parenchymal abnormalities that might help to establish an alternative diagnosis
  • More useful for patients w/ underlying cardiac & pulmonary disease
  • Has a high specificity & sensitivity for central clots
  • The main disadvantage of CTPA to that of conventional pulmonary angiography is that subsegmental clot is less likely to be seen
  • In patients w/ a high pretest probability, negative CTPA may not be able to exclude significant pulmonary thrombi, therefore, these cases may require further investigation (refer to section 6 further work-up)
  • Most experts agree that a patient, in whom CTPA shows PE, may be treated w/o further tests

Further Work-Up

  • Recommended for patients w/ persistent signs & symptoms despite a negative CTPA & D-dimer test

Venous Duplex Ultrasonography (US)

  • Most pulmonary emboli arise from the deep veins of the legs thus it is rational to search for a residual DVT in suspected PE patients
  • Normal US exam of the leg veins does not rule out PE
  • US studies may have false positive or may detect residual abnormalities from past VTE
    • Only definite positive studies under certain clinical circumstances (eg patient w/o history of VTE but has a high clinical probability of PE) should serve as a basis for the start of therapy
  • May improve estimation of the clinical probability of PE & avoid more invasive testing in patients w/ a negative lung imaging study

Ventilation-Perfusion Lung Scanning (V/Q scan)

  • Preferred imaging study when CTPA is contraindicated
  • Normal or near normal lung scans are sufficient to exclude PE, regardless of pretest probability
  • Low probability scans in combination w/ a low pretest probability make probability of PE low
  • High probability scans provide the predictive power to establish diagnosis in context of reasonable clinical suspicion of PE
  • Presence of pulmonary vasculature occlusion of ≥50% may signify massive PE
  • Further tests should be performed in all other combinations of V/Q scan result & clinical probability

Echocardiography

  • Useful for rapid triage in acutely ill patients w/ suspected massive PE
    • Usually reliable to differentiate between illnesses that have radically different treatment compared to PE (eg AMI, pericardial tamponade, infective endocarditis, aortic dissection)
    • May suggest/reinforce clinical suspicion of PE w/ the findings of RV overload & dysfunction in the presence of Doppler signs of increased pulmonary arterial pressure
    • May also definitively confirm diagnosis of PE by visualization of proximal pulmonary arterial thrombi
  • It has not been confirmed if echocardiography can identify patients who would benefit from thrombolytic therapy if they present w/o shock or hypotension

Magnetic Resonance Angiography (MRA)

  • Appears to be promising in human & animal models
  • It avoids ionizing radiation but has a poor sensitivity for subsegmental clots & limited access is likely to continue for several years

Conventional Pulmonary Angiography

  • Historically considered the gold standard for the diagnosis of PE
  • Limitations include: Requirement of expertise in performance & interpretation, it is invasive & there are associated risks
    • W/ subsegmental clot, there can be interobserver disagreement in up to 1/3 of cases
  • Angiography should be reserved for patients in whom noninvasive tests remain inconclusive or are not available
  • Use of pulmonary angiography may also depend on patient’s clinical status & necessity to obtain an absolute diagnosis
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