Pulmonary Embolus

  • Written By: Paul Y. Ko, MD, SUNY Upstate Medical University, Syracruse, New York
  • Edited By: Rahul Patwari, MD, Rush University Medical Center, Chicago, Illinois

Pulmonary Embolus Objectives

  • Discuss the signs and symptoms classic for PE & DVT
  • Use clinical decision rules to develop a pre-test probability for patients with possible PE or DVT
  • Discuss the use of the D-dimer in the diagnosis of pulmonary embolus and DVT
  • Compare imaging modalities used in the workup of patients with suspected thromboembolic disease.

Deep vein thrombosis (DVT) and pulmonary embolism (PE) together comprise a disease process called venous thromboembolism (VTE). A relatively common diagnosis (60,000 hospitalization/year for DVT), VTE may often be deadly, and as such cannot be missed during diagnostic workup in the emergency department (ED).

The deep venous system of the lower extremities includes the:

  • calf veins (anterior tibial, posterior tibial, and peroneal veins),
  • popliteal vein,
  • femoral veins, and the
  • external iliac veins.

The superficial femoral vein, despite its name, is actually part of the deep and not superficial venous system.

VTE can be difficult to diagnosis as patients can present with atypical symptoms and presentation, therefore it is important to have a high index of suspicion and to understand the workup in ruling out this disease process in our ED patients.

Initial Actions & Primary Survey

Initial ABC evaluation of patient presenting with PE is important. Isolated DVT does not typically result in severe morbidity or mortality. The concern with DVT is extension and embolization to the lungs, thereby becoming a PE. PE may present as mild shortness of breath, chest pain, fatigue, or a number of other non-specific symptoms. A massive pulmonary embolism can cause a patient to present in cardiac arrest with PEA (pulseless electrical activity). These patients may need to be intubated initially for airway support.

As with other patients complaining of chest pain or shortness of breath, those with suspected PE should be placed on a cardiac monitor, have IV access, and be supplied supplemental oxygen as needed.

An initial EKG and CXR should be obtained in patients you are concerned about a PE to rapidly evaluate for other items on the differential diagnosis (MI, pneumonia, pneumothorax).

Classic Presentation

Classic Presentation of Deep Venous Thrombosis

Initial DVT symptoms may be subtle and nonspecific. Complaints include general leg pain or a cramping sensation, fullness in the calf, swelling, edema or tenderness on palpation.

The differential diagnosis may include musculoskeletal strain or tear, cellulitis, superficial thrombophlebitis, venous insufficiency, lymphedema, or popiteal (BakerÕs) cyst. Signs of symptoms of the above diagnoses are therefore important to note as pertinent positive and negatives during your physical exam and documentation.

Classic physical examination findings of DVT include unilateral swelling or edema of the extremity, tenderness to palpation, and a palpable venous “cord.” Homan’s sign is the classic sign of pain in the calf on passive dorsiflexion of the foot with the knee in extension. This test is neither sensitive nor specific in ruling in or ruling out DVT of the extremity.

Your initial history and survey should include all the pertinent information to develop a differential and calculate a pretest probability. Risk factors may help estimate the risk of venous thromboembolism in patients and calculate a pretest probability. The Wells score is a clinical decision rule developed to assist in the determining the pretest probability of DVT as well as PE, and to help guide futher diagnostic workup.

Pre-Test Probability (Wells Score) for DVT

Active cancer-treated within previous 6 months (1 point)
Parlaysis, paresis, or recent immobilization (1 point)
Recent bedridden >3 days or major surgery within 12 weeks
requiring general anesthesia (1 point)
Localized tenderness along the distribution of
the deep venous system (1 point)
Entire leg swollen (1 point)
Calf swelling at least 3 cm greater than other side (1 point)
Pitting edema confined to symptomatic leg (1 point)
Collateral superficial veins (non-varicose) (1 point)
Previously documented DVT (1)
Alternative diagnosis at least as likely as DVT (-2 points)
Score: 0=low probability, 1-2=moderate, >3=high

Classic Presentation of Pulmonary Embolus

The classic presentation of PE includes complaints of shortness of breath or chest pain. Additionally, syncope as well as vague complaints of general malaise or functional deterioration may be presenting features. While often vague, patients may describe a pleuritic component to the chest pain (hurts worse with deep breaths). Unilateral leg symptoms (DVT symptoms-see above) may be present, as well as signs of right sided heart failure (jugular venous distention, peripheral edema). The most common vital sign abnormality seen is tachycardia in the setting of normal pulse oxygenation.

Pretest Probability (Modified Wells Criteria) for Pulmonary Embolism

Clinical symptoms of DVT (3 points)
Other diagnosis less likely than pulmonary embolism (3 points)
Heart rate >100 (1.5 points)
Immobilization (3 days) or surgery in the past 4 weeks (1.5 points)
Previous DVT/PE (1.5 points)
Hemoptysis (1.0 points)
Malignancy (1 points)
Clinical Probability: Low probability less than 2, Moderate 2-6, High more than 6

Diagnostic Testing

Clinical decision rules developed for risk stratification of suspected PE include the Pulmonary Embolism Rule Out Criteria (PERC) as well as WellÕs Criteria for PE. These rules can help guide diagnositic testing. In the patient deemed very low risk based on clinical judgement, PERC may be used to support a clinical decision to pursue no further testing. A low-risk patient who passes the PERC rule would not benefit from further testing. A patient who is not judged as lowest risk, or who does not pass PERC, may be evaluated using WellÕs Criteria. WellÕs uses clinical features to determine low, moderate, or high-risk patients. Low risk patients have a low enough pretest probability that a negative d-dimer will essentially rule out PE, while moderate and high risk patients need further workup.

Radiographs

A CXR is useful to rule out other diagnosis such as pneumothorax, congestive heart failure, pneumonia. Sometimes one can see unilateral atelectasis as suggestive of PE, or Hampton’s hump (pulmonary infarct leading to pleural based wedge shaped area of infiltrate) or Westermark’s sign (unilateral lung oligemia).

Note the Hampton’s Hump on the CXR to the left.

X-ray of the lower extremity may be helpful in the workup of DVT if you are concerned about possible skeletal trauma related to the leg pain or swelling.

EKG

EKG findings are usually nonspecific. The most common EKG abnormality is sinus tachycardia, although other findings such as right bundle branch block or evidence of right heart strain (an S wave in lead I and Q and inverted T in lead III, the S1Q3T3 pattern) may be seen.

D-dimer

The utility of a d-dimer directly relates to the pretest probability that the patient has a DVT or PE, as determined above by WellÕs criteria.

D-dimer is a protein derived enzymatic breakdown of cross-linked fibrin. Increased levels indicate the presence of clot formation somewhere in the body. It can be elevated in many diseases, including malignancy, infection, inflammation, MI, strokes, advanced age, and pregnancy and is therefore a very nonspecific test that cannot be used to definitely diagnose any disease process, including DVT and PE. To further complicate matters, there are also several different laboratory techniques of measuring D-dimer that may affect the sensitivity of the test.

Overall, as a test, a D-dimer generally has good sensitivity and negative predictive value, but poor specificity and positive predictive value. In a setting of a patient with a low pre-test probability, a negative d-dimer virtually rules out venous thromboembolism. The d-dimer should not be used in patients with moderate or high pre-test probability, as a negative d-dimer in those patients does not result in a posttest probability low enough to comfortably rule out VTE.

Duplex Ultrasonography

Venous duplex ultrasonography is currently the diagnostic test of choice in most centers for DVT. In the hand of a experienced sonographer, the sensitivity and specificity is approximately 95%.

The classic finding on ultrasound for a positive study is the inability to fully compress the vein in the deep venous system of the leg. Other processes (such as a Baker cyst) can also be seen on ultrasound.

Ventilation Perfusion scan

Patients with a moderate or high pre-test probability for PE should have a imaging study with either CT Pulmonary Aniography (CTPA) or V/Q scan.

To perform a V/Q scan, pictures of the lung are taken while radionuclides are supplied through ventilation (airspace) and perfusion (blood flow). Most areas are both ventilated and perfused. Areas of the lung which are ventilated yet not perfused represent a mismatch and likely pulmonary embolus blocking blood flow. However, various factors affect interpretation of the results, such as preexisting airspace disease, which creates ventilation defects (and therefore possible perfusion defects).

The test becomes relatively useless if patients have other airspace disease, creating ventilation defects.

CT scan

CTPA is now the accepted study to diagnosis PE in most emergency departments. A CT can also show other possible etiologies of the symptoms including pneumonia, masses, effusions, aortic dissection or pneumothorax. Risks include the use of iodinated contrast and its potential for contrast-induced nephropathy as well as radiation exposure. Sensitivity of CT scanning is very high but there are limitations; patients with the highest risk of PE or those whose scans are inadequate should have venous ultrasonography performed to rule out DVT, and then again several days later to evaluate for recurrent DVT after an embolic event.

CT venography can also be used in conjunction with CT pulmonary angiography to evaluate both for PE and DVT. This has the added risk of increased amounts of IV contrast, and additional radiation to the pelvis and extremities.

So how do you make the diagnosis?

All diagnostic labs and imaging should be used in conjunction with your pre-test probability. Although many times a CT thorax or V/Q scan will confirm the diagnosis of a pulmonary embolism, false negatives do occur, and interpretation may be subject to the experience of the radiologist reading it. Therefore a negative CT or V/Q study in a patient with a high pre-test probability should result in further testing or potentially empiric treatment.

Treatment

Those with confirmed PE or DVT on imaging should be treated with anticoagulation. Either unfractionated heparin or low-molecular weight heparins (e.g. enoxaparin) may be used in most cases. This may be started before imaging confirmation in patient with a high pre-test probability of the disease.

Contraindications to anticoagulation include patients with active bleeding (cerebral or GI) as well as patients with previous reaction to heparins. These patients may benefit from having a inferior vena cava (IVC) filter placed. Generally patients with PE should be admitted to the hospital for anticoagulation. Warfarin has a theoretical transient hypercoagulable effect so generally patients are placed on heparin until Coumadin reaches a therapeutic level (INR 2-3).

Thrombolytic therapy in the setting of PE is controversial and indicated in the setting of a massive PE with significant cardiopulmonary compromise or submassive PE with evidence of right heart strain (most commonly echocardiographic diagnosis.)Disposition

Disposition

Generally patients with PE should be admitted to the hospital for anticoagulation. If the PE is large enough to case cardiopulmonary compromise (large A-a gradient, low BP or pulse ox), ICU admission should be considered.

Patients with an isolated DVT without PE sometimes can be set up to receive anticoagulation at home (subcutaneous enoxaparin) with oral anticoagulation (warfarin). This requires teaching and proper coordination with social services and primary care physicians.

Pearls and Pitfalls

  • PE & DVT should be considered as they are common diagnoses with potential fatal outcomes
  • Clinical decision rules such as PERC and WellÕs Criteria help determine pretest probability and guide further workup.
  • The D-dimer is a useful diagnostic test in patients with a low pre-test probability of the disease
  • Neither the CT or V/Q scan are 100% sensitive or specific, so patients with a high clinical pre-test probability may be treated or admitted for further diagnostic workup.

References

  1. Van Belle, A, Buller, HR, Huisman, MV, et al. Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography. JAMA 2006; 295:172.
  2. Wells, PS, Anderson, DR, Rodger, M, et al. Excluding pulmonary embolism at the bedside without diagnostic imaging: management of patients with suspected pulmonary embolism presenting to the emergency department by using a simple clinical model and d-dimer. Ann Intern Med 2001; 135:98.
  3. Fengler, BT and Brady, WJ. Fibrinolytic therapy in pulmonary embolism: an evidence-based treatment algorithm. Am J Emerg Med 2009; 27: 84-95.
  4. Kline JA, Courtney DM, Kabrhel C et al. Prospective, multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost 2008; 6: 772-80.
  5. Stein PD, Fowler SE, Goodman, LR et al. Multidetector computed tomography for acute pulmonary embolism. N Engl J Med 2006; 354: 2317.