Pulmonary Embolism: Difference between revisions

'''Pulmonary embolism''' ('''PE''') is a blockage of the main artery of the lung or one of its branches by a substance that has travelled from elsewhere in the body through the bloodstream ([[embolism]]). Usually this is due to embolism of a [[thrombus]] (blood clot) from the |deep veins in the legs, a process termed [[venous thromboembolism]]. A small proportion is due to the embolization of air, fat, talc in drugs of intravenous drug abusers or amniotic fluid. The obstruction of the blood flow through the [[lung]]s and the resultant pressure on the [[right ventricle]] of the heart leads to the symptoms and signs of PE. The risk of PE is increased in various situations, such as [[cancer]] or prolonged [[bed rest]].<cite>Goldhaber</cite>

Symptoms of pulmonary embolism include difficulty breathing, chest pain on inspiration, and [[palpitation]]s. [[Clinical sign]]s include low blood [[oxygen saturation]] and [[cyanosis]], rapid breathing, and a rapid heart rate. Severe cases of PE can lead to collapse, abnormally low blood pressure, and sudden death.<cite>Goldhaber</cite>

Symptoms of PE are sudden-onset [[dyspnea]] (shortness of breath), [[tachypnea]] (rapid breathing), [[chest pain]] of a "pleuritic" nature (worsened by breathing), [[cough]] and [[hemoptysis]] (coughing up blood). More severe cases can include signs such as [[cyanosis]] (blue discoloration, usually of the lips and fingers), collapse, and circulatory instability due to decreased blood flow through the lungs and into the left side of the heart. About 15% of all cases of sudden death are attributable to PE.<cite>Goldhaber</cite>

The most common sources of embolism are proximal leg [[deep venous thrombosis]] (DVTs) or pelvic vein thromboses. Any risk factor for DVT also increases the risk that the venous clot will dislodge and migrate to the lung circulation, which happens in up to 15% of all DVTs. The conditions are generally regarded as a continuum termed [[venous thromboembolism]] (VTE).

* ''Alterations in blood flow'': immobilization (after surgery, injury or long-distance air travel), [[pregnancy]] (also procoagulant), [[obesity]] (also procoagulant), [[cancer]] (also procoagulant)

There are additional prediction rules for PE, such as the Geneva rule. More importantly, the use of ''any'' rule is associated with reduction in recurrent thromboembolism. <cite>REFNAME9</cite>

Early primary research has shown that in low/moderate suspicion of PE, a normal [[D-dimer]] level (shown in a [[blood test]]) is enough to exclude the possibility of thrombotic PE. <cite>REFNAME13</cite> This has been corroborated by a recent [[systematic review]] of studies of patients with low pre-test probability (PTP) of PE and negative [[D-dimer]] results that found the three month risk of thromboembolic events in patients excluded in this manner was 0.14%, with 95% confidence intervals from 0.05 to 0.41%, though this review was limited by its use of only one randomized-controlled clinical trial, the remainder of studies being prospective cohorts. <cite>REFNAME14</cite> D-dimer is highly sensitive but not very specific (specificity around 50%). In other words, a positive D-dimer is not synonymous with PE, but a negative D-dimer is, with a good degree of certainty, an indication of absence of a PE. <cite>REFNAME15</cite>

When a PE is being suspected, a number of [[blood test]]s are done, in order to exclude important secondary causes of PE. This includes a [[full blood count]], clotting status (PT, [[aPTT]], TT), and some screening tests ([[erythrocyte sedimentation rate]], [[renal function]], [[liver enzyme]]s, [[electrolyte]]s). If one of these is abnormal, further investigations might be warranted.

The gold standard for diagnosing pulmonary embolism (PE) is ''[[pulmonary angiography]]''. Pulmonary angiography is used less often due to wider acceptance of CT scans, which are non-invasive. CT pulmonary angiography is the recommended first line diagnostic imaging test in most people.

CT pulmonary angiography (CTPA) is a [[pulmonary angiogram]] obtained using [[computed tomography]] (CT) with [[radiocontrast]] rather than right heart catheterization. Its advantages are clinical equivalence, its non-invasive nature, its greater availability to patients, and the possibility of identifying other lung disorders from the [[differential diagnosis]] in case there is no pulmonary embolism. Assessing the accuracy of CT pulmonary angiography is hindered by the rapid changes in the number of rows of detectors available in multidetector CT (MDCT) machines. <cite>REFNAME16</cite> According to a [[cohort study]], single-slice [[spiral CT]] may help diagnose detection among patients with suspected pulmonary embolism. <cite>REFNAME17</cite> In this study, the sensitivity was 69% and specificity was 84%. In this study which had a prevalence of detection was 32%, the [[positive predictive value]] of 67.0% and [[negative predictive value]] of 85.2% ([http://medinformatics.uthscsa.edu/calculator/calc.shtml?calc_dx_SnSp.shtml?prevalence=32&sensitivity=69&specificity=84 click here] to adjust these results for patients at higher or lower risk of detection). However, this study's results may be biased due to possible incorporation bias, since the CT scan was the final diagnostic tool in patients with pulmonary embolism. The authors noted that a negative single slice CT scan is insufficient to rule out pulmonary embolism on its own. A separate study with a mixture of 4 slice and 16 slice scanners reported a sensitivity of 83% and a specificity of 96%. This study noted that additional testing is necessary when the clinical probability is inconsistent with the imaging results. <cite>REFNAME18</cite> CTPA is non-inferior to VQ scanning, and identifies more emboli (without necessarily improving the outcome) compared to VQ scanning. <cite>Anderson2007</cite>

''[[Ventilation/perfusion scan]]'' (or ''V/Q scan'' or ''lung [[scintigraphy]]''), which shows that some areas of the lung are being ventilated but not perfused with blood (due to obstruction by a clot). This type of examination is used less often because of the more widespread availability of CT technology, however, it may be useful in patients who have an allergy to [[iodinated contrast]] or in [[pregnancy]] due to lower radiation exposure than CT. <cite>REFNAME19</cite>

Tests that are frequently done that are not sensitive for PE, but can be diagnostic.

*''[[Chest X-ray]]s'' are often done on patients with shortness of breath to help rule-out other causes, such as [[congestive heart failure]] and [[rib fracture]]. Chest X-rays in PE are rarely normal, <cite>REFNAME20</cite> but usually lack signs that suggest the diagnosis of PE (e.g. [[Westermark sign]], [[Hampton's hump]]).

*''Ultrasonography of the legs'', also known as ''leg doppler'', in search of [[deep venous thrombosis]] (DVT). The presence of DVT, as shown on [[ultrasonography]] of the legs, is in itself enough to warrant anticoagulation, without requiring the V/Q or spiral CT scans (because of the strong association between DVT and PE). This may be valid approach in [[pregnancy]], in which the other modalities would increase the risk of birth defects in the unborn child. However, a negative scan does not rule out PE, and low-radiation dose scanning may be required if the mother is deemed at high risk of having pulmonary embolism. {{Citation needed|date=August 2011}}

In massive and submassive PE, dysfunction of the right side of the heart can be seen on [[echocardiography]], an indication that the [[pulmonary artery]] is severely obstructed and the heart is unable to match the pressure. Some studies (see below) suggest that this finding may be an indication for [[thrombolysis]]. Not every patient with a (suspected) pulmonary embolism requires an echocardiogram, but elevations in cardiac troponins or [[brain natriuretic peptide]] may indicate heart strain and warrant an echocardiogram. <cite>REFNAME23</cite>

In most cases, anticoagulant therapy is the mainstay of treatment. Acutely, supportive treatments, such as oxygen or [[analgesia]], are often required.

}}</ref>  A randomised trial of 344 patients (171 outpatients and 168 inpatients) found that outcomes were equivalent whether patients were treated in hospital or at home (there was one death at 90 days in each group).<ref name="Aujesky2011"/><ref>{{cite web

| accessdate = July 4, 2011}}</ref> This confirms the findings of an earlier [[systematic review]] of observational studies. <cite>REFNAME29</cite>

Warfarin therapy often requires frequent dose adjustment and monitoring of the INR. In PE, INRs between 2.0 and 3.0 are generally considered ideal. If another episode of PE occurs under warfarin treatment, the INR window may be increased to e.g. 2.5-3.5 (unless there are contraindications) or anticoagulation may be changed to a different anticoagulant e.g. [[low molecular weight heparin]]. In patients with an underlying malignancy, therapy with a course of [[low molecular weight heparin]] may be favored over warfarin based on the results of the CLOT trial. <cite>REFNAME30</cite>

The use of thrombolysis in non-massive PEs is still debated. The aim of the therapy is to dissolve the clot, but there is an attendant risk of bleeding or stroke. <cite>REFNAME35</cite> The main indication for thrombolysis is in submassive PE where right ventricular dysfunction can be demonstrated on [[echocardiography]], and the presence of visible thrombus in the atrium. <cite>REFNAME36</cite>

If anticoagulant therapy is contraindicated and/or ineffective, or to prevent new emboli from entering the pulmonary artery and combining with an existing blockage, an [[inferior vena cava filter]] may be implanted. <cite>REFNAME38</cite>

Mortality from untreated PE is said to be 26%. This figure comes from a trial published in 1960 by Barrit and Jordan <cite>Barritt</cite>, which compared anticoagulation against placebo for the management of PE. Barritt and Jordan performed their study in the [[Bristol Royal Infirmary]] in 1957. This study is the only placebo controlled trial ever to examine the place of anticoagulants in the treatment of PE, the results of which were so convincing that the trial has never been repeated as to do so would be considered unethical. That said, the reported mortality rate of 26% in the placebo group is probably an overstatement, given that the technology of the day may have detected only severe PEs.