This is part of a recurring series examining landmark articles in Emergency Medicine, in the style of ALiEM’s 52 Articles.
Discussing: Wells, P., Anderson, D., & Rodger, M. (2001). 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. Annals of Internal Medicine, 135(2), 98–107.
Main Points: Wells’ scoring system for risk of PE, when combined with a negative D-dimer, is useful to rule out patients unlikely to have significant illness from PE within the next 90 days.
- This scoring system combined with D-dimer measurement does not accurately identify patients who are likely to have PE at this encounter or subsequent encounters.
Background: Pulmonary embolism (PE) is a common disease (CDC estimates for 2015 are up to 1 in 1,000 persons) and half of patients with PE are not properly diagnosed in the ED due in part to non-diagnostic results of a V/Q scan. This reality presents a diagnostic challenge to ED physicians who are determining which patients should receive a CT scan, and risk stratifying patients for a PE. This study sought to validate the Wells’ Criteria for determining pretest probability of pulmonary embolism in the ED population.
Methods: This was a prospective cohort study of consecutively recruited ED patients at four medical centers in Canada from September 1998 to September 1999. The authors excluded patients with upper extremity deep vein thromboses (DVTs) as the likely source of PE, patients who were symptom free for three days prior to presentation, those who had been on anticoagulation for 24-hours prior to presentation, patients who were not expected to live more than three months after presentation, or anyone who could not get IV contrast, was pregnant, lived too far away for follow-up, or was younger than 18 years of age.
Included patients were risk-stratified by ED physicians based upon the follow criteria:
- Objective clinical signs and symptoms of DVT (swelling and pain over deep vein region, 3 points)
- HR > 100 BPM (1.5 points)
- Immobilization (bed rest, except for using the bathroom, for more than 3 days) or surgery within the past fours weeks (1.5 points)
- Previously diagnosed DVT or PE (1.5 points)
- Hemoptysis (1 point)
- Malignancy (current diagnosis, diagnosis within the last six months, current chemo or palliative care. 1 point)
- PE as the most likely, or equally likely diagnosis (based upon clinical gestalt, 3 points)
A patient with a total score of less than 2 was considered low risk, 2-6 was moderate risk, more than 6 was considered high risk. Each patient’s D-dimer level was then measured, and he or she was evaluated for PE based upon an algorithm that can be found in the article (Figure 1). The evaluation included V/Q scan, bilateral lower extremity ultrasound, and/or pulmonary angiogram based upon risk stratification, D-dimer level, and imaging results.
All participants followed-up at 90 days via phone or in-person to recount events that occurred since the initial encounter.
Results: The data from 930 patients (average age of 50.5 years) were analysed, with prevalence of PE at 90 days found to be 9.5%. PE was diagnosed in 40.6% of patients with high pretest probability, 16.2% in moderate pretest probability group, and 1.3% in the low pretest probability group. These results indicate the negative predictive value of the d-dimer to be 97.3% in the entire cohort, and 99.5% in the low probability group, 93.9% in the moderate probability group, and 88.5% in the high probability group. In this study the Wells’ criteria/D-dimer model demonstrated poor positive predictive value because it only found PE in 16.9% of patients that were indicated to have any level of image testing (V/Q scan, DVT ultrasound, or angiography based upon the algorithm above). Seventeen patients (0.6%) who had PE and DVT ruled out based upon this model had suspicious events for PE or DVT on follow-up, with five of those events confirmed to be a PE or DVT.
While 17 people died during this study, none of the patients who had PE ruled out by the model died from a PE within 90 days of their initial presentation to the ED.
Points to consider:
- Ten percent of the patients enrolled in the study did not have the protocol followed exactly, which limits the external validity of the study.
- There were no imaging tests performed on the low-risk patients, so we cannot accurately say that they did not have a PE, only that they had a low risk of clinically meaningful event over the subsequent 90 days (either diagnosed PE or death).
- This study used the more specific SimpliRED D-dimer rather than the traditional immunoassay linked D-dimer thus decreasing the sensitivity of this model compared to the traditional D-dimer assay.
Further Study: Only 17% of patients who ruled in for testing were found to have a PE, so there is clearly room to increase the positive predictive value of this tool. Fortunately there have been a number of subsequent studies that have tested methods to increase the specificity of this model, and we have included citations to a few of those studies in the related articles below.
Level of Evidence:
ACEP Clinical Policy Grading Level IIB
- V/Q scan was the test that was used to determine presence or absence of PE, and the current standard is CTPA as it is a more reliable test.
- SimpliRED D-dimer was used in this study, not the traditional immunoassay linked D-dimer, which may affect how this criteria applies to patients your department.
- Low risk patients got no V/Q scan, so we cannot be sure of actual incidence of PE in these patients, though they were followed up on so we do know there are few risks to not testing these patients for PE.
Simplification of the revised Geneva score for assessing clinical probability of pulmonary embolism: http://archinte.jamanetwork.com/article.aspx?articleid=414578
Performance of 4 Clinical Decision Rules in the Diagnostic Management of Acute Pulmonary Embolism: A Prospective Cohort Study: http://annals.org/article.aspx?articleid=746965
Diagnostic accuracy of D-dimer assay in suspected pulmonary embolism patients: http://ac.els-cdn.com/S0422763813003166/1-s2.0-S0422763813003166-main.pdf?_tid=4ce51214-6b05-11e5-9303-00000aacb35d&acdnat=1444010801_80598bd9006f6434671a010c02d76997
Wells, P., Anderson, D., & Rodger, M. (2001). Bedside Without Diagnostic Imaging: Management of Patients With Suspected Pulmonary Embolism Presenting To the Emergency Department By Using a Simple Clinical. Annals of Internal Medicine, 135(2), 98–107.
ACEP Clinical Policy Committee. (2003). Clinical Policy: Critical Issues in the Evaluation and Management of Adult Patients Presenting With Suspected Pulmonary Embolism. Annals of Emergency Medicine, 41(2), 257–270.
Anderson, D. R., & Barnes, D. C. (2009). Computerized tomographic pulmonary angiography versus ventilation perfusion lung scanning for the diagnosis of pulmonary embolism. Current Opinion in Pulmonary Medicine, 15(5), 425–429.
Brown Ultrasound Tape Review – 9:3:2015
Article #1: Increased ICP via Optic Nerve Sheath Diameter (ONSD)
Amini, et al. (2013). Use of the Sonographic Diameter of Optic Nerve Sheath to Estimate Intracranial Pressure. American Journal of Emergency Medicine 2013; 31: 236–239.
In this 2013 study, Amini et al measured the ONSD of 50 non-traumatized patients undergoing LP and found that an ONSD >5.5mm correlated with an ICP >20mm Hg with a sensitivity and specificity of 100%. While this sounds great, we discussed well known concerns regarding inter-operator reliability and the technical aspects of accurately measuring the ONSD; measuring Optic Disc elevation is an alternative strategy.
The bottom line: while normal ONSD measurements cannot rule out increased ICP, it may be a useful adjunct in patients with low pre-test probability.
Article #2: Proximal Lower Extremity DVT
Crisp, et al. (2010). Compression Ultrasonography of the Lower Extremity with Portable Vascular Ultrasonography Can Accurately Detect Deep Vein Thrombosis in the Emergency Department. Annals of Emergency Medicine 2010; 56 (6): 601-611.
In this 2010 study by Crisp et al, 47 ED physicians performed “2 Point Compression” on the Common Femoral and Popliteal veins in 199 patients, and their results were compared to the “comprehensive” results from the Department of Radiology studies that each patient also received. The physicians took a 10 minutes training session, and the test was “positive” if a thrombus was visualized, or if the vein was non-compressible. When compared to the Radiology results, the ED docs were 100% sensitive and specific for DVTs in these locations. Our discussion centered around whether calf veins (which 2 Point Compression does not search for) are worth searching for (no one knows).
The bottom line: 2-point compression with a D-Dimer (and follow up comprehensive study if positive) may be an acceptable strategy for the management of DVT in the ED.
Special thanks and credit to Jon Thorndike
(OK, you don’t actually have to print it on real paper, but know that it is, in fact, available printed on paper in the leading medical education journal. Or you can just point and click. For free.)
The rapid expansion of free, open-access medical edutainment has led us headlong into debate. To sum up the discussion, these two letters to the editor refer to a previously-published article by Mike Mallin, an emergency physician and EM educator in Utah, and colleagues surveying the use by EM residents of asynchronous education resources, which they define as “a student-centered modality of teaching which involves sharing online learning resources and promotes peer-to-peer interactions,” and which includes podcasts, blogs and other online shareable media. (3) Known collectively/colloquially as FOAMed (Free Open-Access Meducation), these resources are now part and parcel of many EM training programs, able to be consumed at one’s own pace, on one’s own time.
Pescatore and colleagues, in their letter to the editor, worry aloud that the messages trumpeted via asynchronous resources are at risk of being interpreted as gospel truth by unsuspecting consumers without critical consideration of their merits. Particularly susceptible to this, they argue, are the most popular of these resources and the most junior of consumers. They cite a discussion about treatment of infant bronchiolitis on an episode of the EM:RAP podcast wherein a popular contributor to that podcast made a treatment recommendation that is not supported by – and may be frankly frowned upon – by national societies in pediatrics (and which, in fact, may have been dangerous). If taken as truth rather than opinion – a real risk when impressionable listeners are swayed by the near-celebrities on popular sites – this may lead to an increase in an arguably unsafe practice. Continue reading