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SGEM#119: B-Lines (Diagnosing Acute Heart Failure with Ultrasound)

SGEM#119: B-Lines (Diagnosing Acute Heart Failure with Ultrasound)

Podcast Link: SGEM119
Date: April 14th, 2015

Guest Skeptics: Dr. Alan Chiem. Alan is an assistant clinical professor and the director of ultrasound at UCLA Olive View.

Case: 78 year old man with a history of diabetes, hypertension and coronary artery disease presents with a two day history of increasing shortness of breath. He does not have any chest pain or fever. You have been doing more and more with ultrasound and wonder whether you can make the diagnosis of acute pulmonary edema before getting the standard CXR, ECG and lab tests.

Background: Acute heart failure is a condition where the heart cannot pump well enough to meet the demands of the body. It can be due to a number of different causes including: myocardial infarction, arrhythmias, valvular dysfunction, pneumonia, uncontrolled hypertension, anemia, hyperthyroidism and many other causes.

The diagnosis of heart failure before the 1990’s was fairly grim with 60-70% of patients dying within five years of diagnosis.

Things have improved tremendously over the last couple of decades with respect to mortality but heart failure is still the most common re-admission diagnosis within one month for patients over 65 years of age. In the U.S. we spent roughly 25 billion every year on acute heart failure hospitalizations alone.

The diagnosis of acute heart failure can be challenging because the signs and symptoms are insensitive and/or non-specific.

Clinical gestalt alone is moderately specific, but not sensitive (LR+ 4.4, LR- 0.45). Chest x-rays have been used for years to diagnose heart failure, but is also imperfect. For example the presence of interstitial edema has LR+ 17.1 but LR- only 0.7. In addition, chest x-ray interpretation agreement between radiologist and emergency physician can be less than 50%. This could result in many patients with acute heart failure being missed.

Serum markers of BNP and ProBNP sometimes help diagnose patients with acute dyspnea. A systematic review by Lam et al in Ann of Intern Med 2010 demonstrate ED testing may decrease hospital LOS by a day, and possibly reduce admission rates, but they did not really affect mortality rates. http://pmid.us/22123173

B-Lines via Matt Dawson

B-Lines on Ultrasound Via Matt Dawson

In 2012, BEEM and Dr. Peter Rosen published a review of 5 diagnostic RCTs that explored ED physician awareness of BNP or not (J Emerg Med). This study noted no consistent differences in any measurable outcome (diagnostic accuracy, ED length of stay, hospitalization rates, length of hospital admission, etc.)

POCUS is now part of the core curriculum for emergency medicine residents. Identifying B-Lines on thoracic ultrasound can be used to identify interstitial fluid.

Clinical Question: Can novice emergency medicine resident physician sonographers accurately identify B-lines in undifferentiated dyspnea patients to diagnose acute heart failure after a 30-minute training course?

Reference: Chiem AT, et al. Comparison of expert and novice sonographers’ performance in focused lung ultrasonography in dyspnea (FLUID) to diagnose patients with acute heart failure syndrome. AEM April 2015

  • Population: Sixty-six EM resident physicians from one inner-city ED with over 100,000 annual visits assessing patients >18 years old presenting with chief complaint of dyspnea.
    • Exclusion criteria included attending physician perspective that dyspnea due to cause other than CHF, incarcerated individuals, patients who were pregnant, on dialysis, on positive pressure ventilation, or receiving nebulizer treatment, or too ill to provide written consent. Non-English speaking patients were also excluded.
  • Intervention: Bedside ultrasound by EM resident assessing for three or more B-lines using eight-zone thoracic ultrasound on thoracic exam preset and curvilenear transducer. All EM residents received 30-minute lecture on technique and recognition of sonographic B-lines by the ED director of ultrasonography.
  • Comparison: No comparison group
  • Outcome:
    • Primary Outcome: Diagnostic accuracy (sensitivity, specificity, positive/negative likelihood ratio, positive/negative predictive value) of novice sonographers to identify B-lines by bedside ultrasound compared with an expert sonographer.
    • Secondary Outcome: Diagnostic accuracy of both novice and expert sonographers’ interpretation of ultrasound B-lines to diagnose acute heart failure syndrome, using two independent expert’s chart review as the criterion standard.

Authors Conclusions: Inexperienced sonographers can identify sonographic B-lines with greater than 80% sensitivity and specificity as compared to an expert sonographer after a brief tutorial. Lung ultrasonography has fair predictive value for pulmonary edema from acute heart failure in the hands of both novice and expert sonographers.

checklist-cartoonQuality Checklist for Diagnostic Trials:

  1. The clinical problem is well defined. Yes – Bedside exam is inaccurate and often unreliable for the diagnosis of CHF as the etiology of acute undifferentiated dyspnea in ED patients.
  2. The study population represents the target population that would normally be tested for the condition (ie no spectrum bias). Yes
  3. The study population included or focused on those in the ED. Yes
  4. The study patients were recruited consecutively (ie no selection bias). No
  5. The diagnostic evaluation was sufficiently comprehensive and applied equally to all patients (ie no evidence of verification bias). Unsure
  6. All diagnostic criteria were explicit, valid and reproducible (ie no incorporation bias). Unsure
  7. The reference standard was appropriate (ie no imperfect gold-standard bias). Yes
  8. All undiagnosed patients underwent sufficiently long and comprehensive follow-up (ie no double gold-standard bias). Yes
  9. The likelihood ratio(s) of the test(s) in question is presented or can be calculated from the information provided. Yes
  10. The precision of the measure of diagnostic performance is satisfactory. Yes

Key Results: Although EM residents not mandated to participate, 92% did with range of 1 to 28 ultrasounds and median of 3 per sonographer.

Over 50% of 1200 dyspnea patients presenting between May 2009 and June 2010 were ineligible using the authors’ criteria and 380 patients were included in the analysis (93% African American, mean age 55 years).

Acute heart failure syndrome was the cause of dyspnea in 35% of patients with a 92% agreement for CHF-as-cause between the two expert reviewers.

  • Primary Outcome: Diagnostic accuracy of novice sonographer to identify B-lines for each lung zone
    • Sensitivity 85% (95% CI 83%-88%) and Specificity 84% (95% CI 82%-85%)
    • LR+ 5.2 (95% CI 4.7-5.8) and LR- 0.2 (95% CI 0.1-0.2)
  • Secondary Outcome: Diagnostic accuracy of linking B-line identification to the correct diagnosis of CHF
    • Novice Sonographers:
      • Sensitivity 87% (95% CI 81%-92%) and specificity 49% (95% CI 42%-55%)
      • LR+ 1.7 (95% CI 1.5-2.0) and LR- 0.3 (95% CI 0.2-0.4).
    • Expert Sonographers
      • Sensitivity 85% (95% CI 78%-90%) and specificity 58% (95% CI 52%-64%)
      • LR+ 2.1 (95% CI 1.7-2.4) and LR- 0.3 (95% CI 0.2-0.4)

The Receiver Operating Characteristic Area Under the Curve was 0.77 (95% CI 0.72-0.82) for novice sonographers and 0.76 (95% CI 0.71-0.82) for expert sonographer.

Screen Shot 2015-04-25 at 3.11.12 PM1) This was a fascinating Level II Diagnostic Accuracy study exploring the reproducibility of ideal setting bedside sonography (handful of experts) in the real-world of mostly inexperienced EM sonographers.

Dr. Alan Chiem

Dr. Alan Chiem

  • I would argue that we are not making the diagnosis of acute heart failure, especially as it relates to type and severity, in a timely manner. Acute heart failure syndrome, being a syndrome, can occur from several etiologies and there are guidelines as to how best to treat a specific phenotype.
  • However, most clinicians assume that all patients with acute heart failure have the same hemodynamic issues and therefore manage them with nitrates and furosemide. This leads to complications such as hypotension and acute kidney injury, with associated increases in length of stay as well as mortality. This is one of the reasons that heart failure researchers are starting to look at ED-based enrollment, so that you can potentially identify acute heart failure type and severity, in order to tailor therapies and to potentially identify patients that improve dramatically in the ED for discharge.
  • POCUS (especially focused echocardiography) can really help with this problem, because it looks as patients’ hemodynamics in a way that no lab or imaging test can capture. I firmly believe that EP’s can be trained to do an acute heart failure ultrasound protocol, and the UCLA Clinical Science Testing Institute has given me some funding to test this out.
  • However, one of the key issues in POCUS is the balance between feasibility and accuracy. We want to be able to prove to clinicians that the amount of training involved in the ultrasound application is outweighed–and we hope by a large extent–the increase in clinical accuracy and efficiency. In using a large group of trainee physicians, this study is a good step in that direction, whereas the vast majority of studies use a small group of highly-trained clinician sonologists.

dreamstime_m_23118315Hierarchy of Evidence for Diagnostic Studies:

  1. Technical Efficacy – can we obtain the measures for diagnosis
  2. Diagnostic Accuracy Efficacy- sensitivity, specificity, likelihood ratios, predictive values and area under the curve
  3. Diagnostic Thinking Efficacy – confidence in diagnosis
  4. Therapeutic Efficacy – proportion of cases that further testing we avoided and changed management
  5. Patient Outcome Efficacy – cost per unit of change in outcome variable, morbidity avoided by testing, mortality
  6. Societal Benefit – cost effectiveness analysis from society perspective

2) The authors used appropriate chart review methods and adhered to the important elements of the Standards for Reporting of Diagnostic Accuracy (STARD) guidelines.

  • We attempted to follow the 25-point checklist, including reporting the number of patients excluded and exclusion reason, as well as blinding of ultrasound interpretation and ultimate primary diagnosis.

3) The reporting a kappa value rather than raw agreement in assessing the cause of dyspnea, as acute heart failure syndrome between two experts would have been more meaningful.

  • This was considered but was was not a primary outcome of interest. Rather, two expert reviewer diagnosis (which should take into account the clinical, laboratory, and imaging data presented) is the gold standard in acute heart failure studies.

4) We were uncertain whether expert chart reviewers were aware of the bedside ED ultrasound results when determining whether cause of dyspnea was congestive heart failure; if they were aware then incorporation bias would tend to increases estimates of sensitivity and specificity.

  • The expert reviewers were blinded to the ultrasound results. However, the study sonologists were not necessarily blinded to the clinical information at hand as they performed and interpreted the ultrasounds. However, the expert sonologist who reviewed the ultrasounds and made his own interpretation was blinded to all data. It is interesting to see the differences in false positive and negative rates among the two groups.

5) If ED clinicians used findings of B-lines to determine subsequent congestive heart failure (or other diagnostic) testing, partial verification bias increases estimates of sensitivity and decreases estimates of specificity.

  • This was largely avoided this issue because the ultrasound results were not available to the expert reviewers. We don’t think it influenced diagnosis since the expert reviews are based on primarily laboratory and imaging data, as well as discharge summaries. In fact, most internists and cardiologists have no idea what a B-line is when you ask them. They assume that you are talking about Kerley B-lines on chest radiographs.

roccomp6) You reported Receiver Operating Characteristics as Area Under the Curve (AUC). The AUC helps us estimate how good a test is at discriminating between disease and non-disease. To construct a ROC graph, we plot these pairs of values on the graph with the 1-specificity on the x-axis and sensitivity on the y-axis. The result can be between -1 and +1 with a perfect test having a value of 1. Your results were in the “good” range with both resident and attending having a value of 0.77 and 0.76 respectively.

  • An ROC curve looks at the signal to noise ratio of a test, by graphing the true positive rate (or sensitivity) to the false positive rate (or 1-specificity) of various points of the test, in order to arrive at an optimal cut-off. However, you can look at the area under the curve and use it to see in general how accurate the test is.

Comment on authors conclusion compared to SGEM Conclusion: We agree that inexperienced sonographers in a setting with ongoing ultrasound curricula and mentoring expertise can quickly acquire the skill to accurately identify B-lines by bedside ultrasound.

However, we are uncertain if this would be the same in settings without ultrasound expert to teach knobology, probe position, enhancing image quality, and facilitate balance between ED workflow and implementation of a new ultrasound skill.

  • Clinical ultrasonography is a rapidly expanding field. We are currently seeking subspecialty board certification.

Bedside ultrasound has two distinct skill requirements: (1) image acquisition and (2) image interpretation. Other imaging modalities (x-ray, CT, or MRI) do not require the ED provider to acquire the images.

  • That is true. It places imaging into the hands of clinicians and allows for expedited diagnosis in optimal circumstances. Both subsets need to be introduced relatively early in training, because we know that after training, it becomes more difficult to learn such a potentially powerful but difficult way to practice. That’s why most of us ultrasound gurus are also busy introducing ultrasound to medical students in anatomy and physical diagnosis courses, as well as teaching our emergency medicine trainees and colleagues.

Part of “knowledge translation” in bedside ultrasound is learning how to efficiently obtain images without disrupting busy ED workflow. Doing so for congestive heart failure, where a reasonably accurate and readily available test (chest x-ray) already exists, requires research in non-academic, non-ultrasound training EDs.

Additionally, the clinical impact of bedside ultrasound was not assessed in this study. Using the most accurate measures of bedside US for B-lines (LR+ 2.1, LR- 0.3 for expert sonographer), the 35% pre-test probability for CHF would increase to 53% with a positive ultrasound and 14% with a negative ultrasound.

Is this post-test shift is CHF probability meaningful? What are the test- and treatment-thresholds upon which individual clinicians alter subsequent management decisions?

These questions will only be answered with a diagnostic randomized controlled trial where half the dyspnea patients ED provider point-of-care ultrasound, half do not. This diagnostic RCT should assess ED length of stay, admission rates, ancillary testing, and total costs, but also patient-centric outcomes like time to relief of symptoms

  • The +LR 2.1 and -LR 0.3 is for 1/8 positive zones. B-lines can result from ARDS as well as para-pneumonic processes as well, especially if they are unilateral and/or if they are associated with sub-pleural consolidations, which we did not study. However, when all 8 zones have more than 3 B-lines, the +LR goes up to 9.2. What I’d like listeners to take away from this study is that with someone where there is reasonable suspicion that pulmonary edema is the cause, just doing B-line ultrasonography on two anterior zones gives a +LR of 4-5, with specificity for pulmonary edema of greater than 90%.

SGEM Bottom Line: Bedside ultrasound by inexperienced EM residents in a training program with an ultrasound fellowship to identify B-lines in non-critical ED patients with undifferentiated dyspnea is just as accurate as ultrasounds by experienced sonographers.

Whether this applies to non-academic settings without ultrasound expertise is unknown. If the diagnostic accuracy is confirmed in less academic settings, future studies should assess more meaningful outcomes than diagnostic accuracy such as length of stay, admission rates, ancillary testing, and resolution of patient symptoms.

Case Resolution: You get out the ultrasound machine and find B-Lines suggestive of acute heart failure. These ultrasound findings are verified by your attending.

While happy to have your skills confirmed you continue the work-up for the underlying cause of the patient’s dyspnea.

Clinically Application: Bedside ultrasound in dyspnea patients by inexperienced EM residents to identify B-lines with minimal training is accurate relative to more experienced sonographers. However, using ultrasound B-lines to rule-in (LR+ 1.7) or rule-out (LR- 0.3) CHF is problematic and somewhat underwhelming.

What do I tell my patient? There are many potential causes for your shortness of breath. One possibility is heart failure and several tests will help to assess this possibility. One test that we can conduct right now is an ultrasound of your lungs. The results of this test may help me to more quickly determine the probability of acute heart failure while more definitive tests are pending.

Keener Kontest: Last weeks winner was Greg Costello. He knew cows eating spoiled silage were noted to be having bleeding disorders in Wisconsin. Scientists at the University of Wisconsin found the chemical responsible for the bleeding and licensed it to DuPont, which continues to pay royalties to the University of Wisconsin Research Foundation (WARF). DuPont’s formulation of warfarin sodium is called Coumadin.

Listen to the podcast for this weeks keener question. If you know the answer send an email to TheSGEM@gmail.com with “keener” in the subject line. The first correct response will win a cool skeptical prize.

Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.

Conferences:

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  • Great article and discussion! I have a few observations:

    Bedside ultrasound has three distinct skill requirements: image acquisition, image interpretation, and image integration into care paths. I am able to generate an image of B-lines, I can recognize the B-lines, but can I put this finding into proper clinical context? As mentioned in the discussion above, B-lines are created by processes that create interstitial thickening which can include not only CHF, but interstitial pneumonia, ARDS, contusion, and fibrosis. How good am I at figuring out if which of these aetiologies best fits? Could there be more than one cause involved? The 8-zone positive patient is great but there are many who will not fit this pattern. Inexperienced clinicians (whether ultrasound savvy or not) may not be as good with this final step.

    Ultrasound research is trapped between assessing the untrained/minimally trained and the single highly experienced power user. From a research perspective this is understandable. The time and resources to train a large group of study participants in a skill is a huge barrier to recruitment. We also want to show the untrained masses that they should pick up a probe immediately and save lives. But I would argue it is not a fair assessment of this relatively new modality. These studies are great pilot projects but we need to move to the next step of properly training a larger group of participants in multi-centre settings.

    We know ultrasound is a user-dependent skill with a significant learning curve. It is analogous to running trials on how well a new surgeon does with laparoscopic appendectomies with a one hour teaching session and comparing this to surgeons with residency-long training (plus post graduate practice experience) in open appendectomy. Is this really the best way to test how effective a new procedure can be to patient care?

    In addition, the use of a single ultrasound finding potentially limits accuracy as well.
    It is like only auscultating the lungs but not assessing vitals, heart sounds, peripheral edema, etc. when putting together the whole clinical picture.

    I would like to see more studies where ultrasound assessment of heart failure includes ultrasound imaging of the heart, IVC, lungs (and even extremities if DVT/PE is suspected). Looking for signs of pulmonary effusion, consolidation, and pleural changes are helpful in further delineating aetiology of dyspnea.

    For example, Pirozzi, et al. Critical Ultrasound Journal 2014, 6:5 looked at early use of POCUS in assessing patients with dyspnea and demonstrated marked improvement in accuracy of early diagnosis from 50% to 95%.

    Another factor to consider is that ultrasound shows pulmonary edema before Xray and demonstrates response to therapy real-time, much faster than Xray. Thus the clinician can rapidly assess how their therapy is working and potentially avoid over-diuresis.

    As we develop a greater number of physicians well trained in ultrasound image generation, interpretation, and integration into patient care, I think we will have more success in determining patient-oriented outcome effect.

    • TheSGem

      Thank you Greg for taking the time to comment on the #SGEMHOP. You provide some very good insight into the issue of using B-Lines to diagnose acute heart failure.

      There does seem to be a divide between untrained/minimally trained and power users. This will change as the new residents work through system and become attendings.

      Having more studies as suggested will be helpful. Thank you for sharing the article from Pirozzi et al.

      We need to get a Canadian Ultrasound guru like you on the SGEM:)

  • Paul Olszynski

    Great review and great comments from Dr. Greg Hall. I echo his sentiments re: novice/expert divide found in current PoCUS research – it is limiting the impact of the intervention (as alluded to in the podcast as well). Take your smart phone for example: if we only studied phone calls to determine its impact on our lives, the results would be underwhelming. Add email, twitter, various med apps, texting, camera and more, and now you start to really get an appreciation of impact.
    PoCUS for dyspnea is the same, and includes various lung, cardiac and other views. As mentioned already, when combined, they can significantly assist with diagnostic accuracy and patient flow.
    Cheers,

    • TheSGem

      Thanks for your comments Paul.
      I like your last sentence about PoCUS.
      When a tool is used correctly in the ED it can improve care and flow.

  • Alan Chiem

    Thank you again for the opportunity to appear on SGEM, as well as the excellent comments.

    Yes, I agree that having a protocol involving assessment of LV systolic and diastolic function and IVC, in addition to B-lines, will improve specificity as well as the ability to identify AHF etiology.

    However, this takes more training and time to perform. So we should convince our novice sonologists of the benefit of a relatively simple US procedure like B-line identification first. When that is practiced more commonly, then I think we can approach more complex protocols. But the time and training required for each addition should be outweighed by the incremental increase in diagnostic accuracy.

    Also, to contextualize the likelihood ratios from our study, assuming an AHF prevalence of 30% (or pretest probability), this is the probability of AHF as the cause of dyspnea if there are:

    No positive zones= 10%
    1/8 zones= 50%
    Bilateral anterior zones= 70%
    All 8 zones= 80%

    Thanks again,
    Alan

    • TheSGem

      Great having you on the #SGEMHOP episode. Cutting the KT window down to <1 month. Best feedback, comments and tweets will be published in future AEM.

  • Peyvand Ashtarani

    I am a family doctor practicing in rural part of Ontario at
    the moment. I have practiced in different size communities and hospitals over
    the years. I believe whatever we learn will be of a use in the future.

    Clinical skills and ultrasound are the two crucial adeptness
    which will save lives in the rural settings. I have been using ultrasound
    during the 1.5 years. I have noticed a huge difference in my competency and I
    can diagnose and perform procedures which I was never able to do them before.
    In most places in the world we do not have the luxury of having imaging, labs,
    specialist support at all times. Transportation is not always that easy either.

    I diagnosed and transferred an ectopic pregnancy in just 20 minutes
    in the evening in our little hospital but in tertiary center obstetric service
    waited for formal ultrasound for over 10 hours to confirm the diagnosis. I
    removed a broken needle in a foot which was there for over a month and patient
    was walking on it every day. X-ray could not mark it properly and it was
    impossible for me to remove it without ultrasound. I diagnosed appendicitis in
    a 51 years old woman with diarrhea and mild abdominal pain which could have
    been diagnosed as gastroenteritis without ultrasound. I diagnosed a tamponade in a cancer patient with hypotension which
    was initially diagnosed as cardiomyopathy due to cancer, chemotherapy and
    radiation.

    Since many years ago when smart ER doctors in Germany and
    Japan started to use ultrasound for trauma patients in Second World War, we
    have found many other uses for ultrasound and I suspect that we will use
    ultrasound for almost all the patient in the near future. Ultrasound is a new
    stethoscope for 21 century.

    I want to thank you all for this podcast. We should spread the word. Ultrasound
    training should be started in medical school and any doctor should use it like
    a stethoscope.

  • Peyvand Ashtarani

    I am a family doctor practicing in rural part of Ontario at
    the moment. I have practiced in different size communities and hospitals over the years. I believe whatever we learn will be of a use in the future.

    Clinical skills and ultrasound are the two crucial adeptness
    which will save lives in the rural settings. I have been using ultrasound
    during the 1.5 years. I have noticed a huge difference in my competency and I can diagnose and perform procedures which I was never able to do them before. In most places in the world we do not have the luxury of having imaging, labs, specialist support at all times. Transportation is not always that easy either.

    I diagnosed and transferred an ectopic pregnancy in just 20 minutes
    in the evening in our little hospital but in tertiary center obstetric service
    waited for formal ultrasound for over 10 hours to confirm the diagnosis. I
    removed a broken needle in a foot which was there for over a month and patient was walking on it every day. X-ray could not mark it properly and it was impossible for me to remove it without ultrasound. I diagnosed appendicitis in a 51 years old woman with diarrhea and mild abdominal pain which could have been diagnosed as gastroenteritis without ultrasound. I diagnosed a tamponade in a cancer patient with hypotension which was initially diagnosed as cardiomyopathy due to cancer, chemotherapy and radiation.

    Since many years ago when smart ER doctors in Germany and
    Japan started to use ultrasound for trauma patients in Second World War, we have found many other uses for ultrasound and I suspect that we will use ultrasound for almost all the patient in the near future. Ultrasound is a new stethoscope for 21 century.

    I want to thank you all for this podcast. We should spread the word. Ultrasound training should be started in medical school and any doctor should use it like a stethoscope.

  • Daniel Theodoro MD

    I have a confession. I’ve always been skeptic of B lines on
    ultrasound for CHF. I’m skeptical because I guess (albeit incorrectly based on the gestalt data above) I trust my clinical acumen for making a presumptive diagnosis of CHF. If my pretest prob were 35% I think I would lean strongly towards admission. Maybe this will/should change with healthcare reform.
    But here’s my next confession. Thirteen years after my EM
    ultrasound fellowship I’ve come around—a bit. I still feel there’s a grey data
    zone (no pun intended) where I see a B line, then it goes away, then I see 3,
    then they go away and I’m still flummoxed. But every now and then I get 3 comet tails lighting up the dark universe of diagnostic uncertainty and at least I feel better about my thinking! Oh and I think novices are about as good as experts in this because it’s just not that hard. But I agree that there are other clinical variables that would make a more experienced EP take the findings differently than say a first or second year resident. Although I think in the context of the study (non-critically ill patients) ARDS would be (hopefully) excluded. I see EPs using the technology with the smoker without a diagnosis of COPD that is mildly swollen and SOB.
    The one tidbit I can offer is this: Lichtenstein, a pioneer
    in pulmonary ultrasound probably deserving of the title, “Founding Father,” did not use really advanced probes. He had a cardiac probe. Why is this important? Well pulmonary ultrasound is based on interpreting “artifacts.” That means what you see is really not there anatomically. It’s the result of what happens to sound waves as they echo back at the probe lung tissue (wet and dry) and air in the lungs. So, in this case, using less “advanced” technology might work to your advantage. So my big tip is pick the “least best” probe you have for the application (usually a phased array set on abdominal) and see if that makes it easier for you.

    PS: love the reviews. Especially on what study design and
    outcomes we should use for the next big step! Gets my research noggin’ going!

    You can follow me on twitter: @TeddyDaniels

    • TheSGem

      Glad to hear you “love” the reviews and it has stimulated your research noggin’

  • This is a great study, and one that I’m happy is out there. As far as the primary outcome, I think it answers this question very well: how accurate are novice sonographers at detecting b-lines compared to the expert sonographers. My question is not about the primary outcome, but rather the secondary outcome. The secondary outcome looked at how accurate EM sonographers were at using b-lines to diagnose heart failure exacerbations.

    The international lung ultrasound consensus statements defines pulmonary edema as >3 b-lines in 2 or more zones in each side (using 4 zones on each hemothorax), and when just that criteria is looked at, novice sonographers had a sns of 57% and a spc of 84%, +LR of 3.5 and a -LR of 0.5, while expert sonographers had a sns 38% and a spc 89%, +LR of 3.4 and -LR 0.7.

    To me, this is odd. Most of the studies I’ve read report a much higher accuracy for b-lines in the undifferentiated SOB patient. For instance, study that came out in chest this year (PMID: 25654562) included 1005 dyspneic patients and reported US to be 90.5% sensitive and 93.5% specific with +LR 14 and -LR 0.1 for acute decompensated heart failure (ADHF).

    Any thoughts as to why the discrepancy?

    • TheSGem

      I will see about Alan getting your some thoughts on this question.

  • Alan Chiem

    Jacob, good to hear from you and thanks for the comments!

    Regarding your question about the discrepancy in results from FLUID and other studies:

    One issue may be the definition of positivity. You mentioned in the lung US consensus statement
    about 2 or more positive zones bilaterally, but you can also do the abbreviated anterior two-region scan (B-D2-S2). There is not a set standard based on evidence. Even in the meta analysis by Al Deeb et al, there was not a set standard definition of positivity used. In addition, most of these studies involved patients in the ICU, where you would expect a higher likelihood of AHF patients or more difficult blinding sonographers to patient diagnosis because they’ve already had work-ups initiated. The ETUDES study by Andrew Liteplo and Vicky Noble is most similar to FLUID. It included 94 ED patients and 7 sonographers, and had similar +LR of 3.9 (95% CI, 1.6-9.7) and -LR 0.5 (95% CI, 0.3-0.8) for the same positivity definition.

    I haven’t had a chance to review the Pivetta et al paper in CHEST due to access issues, but I’m a firm believer in B-line ultrasonography and their results will definitely lend to wider adoption of the application.

    The differences in our results probably lie in the sample population as well as the methodology. Were all patients recruited consecutively to minimize selection bias? We attempted to do this in
    FLUID with research associates working set research shifts in the ED to recruit patients. Who were the subjects and what was their pretest likelihood of disease? For FLUID, we excluded patients that clearly had another cause of dyspnea, or were too sick (e.g., on BiPAP) to participate; so we looked at the middle of the spectrum where lung US is most likely to benefit. Our prevalence
    of AHF was 35%, which is similar to the Anderson et al and ETUDES study. What was the training of the study sonologists? Was it the same as our group of 66 novice sonologists or more advanced? Were they blinded to other imaging and lab criteria? Also, were the expert reviewers blinded to the US results? To the CXR and BNP results? If they are making the final diagnosis based on any of these, while at the same time comparing CXR, BNP, and US findings, then this leads to incorporation bias, which would inflate the accuracy estimates.

    Interestingly, though, Pivetta et al found that BNP had a lower accuracy estimate than US. I would
    expect the opposite, since the clinical teams are more likely to use BNP and CXR for the diagnosis, and their management–as reviewed by their discharge summaries–are typically used by independent expert reviewers to make the diagnosis of AHF or not.

    Thanks again for your comments!

  • Resuscitation

    The likelihood ratios from the papers cited are not as good at shifting from pre to post test probability in the intermediate pretest population as one might expect from a test that we would use in emergency medicine. Perhaps the message from these likelihood ratios is “Don’t use this test alone to rule in or rule out CHF.” To be clear, even the expert emergency
    physician would use clinical gestault, history, physical findings, laboratory
    findings, CXR, and lung ultrasound to create a differential diagnosis. This is
    strengthened by the fact that the gold standard in most CHF studies is actually expert chart review and the agreement of two physicians in studies.
    It seems the divide between ‘less’ trained and ‘more’ trained in this study was small (AUC was very similar). It is tremendously challenging to determine what the “truth” about lung ultrasound is in heart failure until we have consistency in practice. The International guidelines on lung ultrasound will go a long way at establishing some consistency but the user-dependency of ultrasound will always be a ‘problem.’ Radiologists have overcome this by accepting that those people who receive training and perform the test in clinical practice will also perform it in research. This means the centre-specific variability exists. For example, at Andrew’s centre sensitivity of ultrasound for appendicitis is not as good as he would expect. At HSC (less than an hours drive away) the sensitivity is 95%+.
    Likelihood ratios are useful in telling us how much to shift our pretest probability in a particular patient relating to the diagnosis of congestive (acute) heart failure. Patients present along the continuum with some being in greater and lesser degrees a congestive heart failure. Ultrasound in these patients must be used in conjunction with other data as mentioned above in order to make the diagnosis accurately.
    We are in an evolution of learning lung ultrasound for the diagnosis of CHF. As the population of physicians knowledge and skill surrounding lung ultrasound increase this modality will likely have a greater database to support its use and uptake. The likelihood ratios for the diagnostic
    capability of this test are moderate in strength so we should remain
    appropriately skeptical when applying it to the clinical setting and integrate
    it with other information about the patient giving it the appropriate weight.

    Andrew Healey MD
    Mark Mensour MD

    • Alan Chiem

      Thank you for the comments, Andrew, Mark, and Chris!

      FLUID did not incorporate the sonologists’ clinical gestalt to determine a pretest probability of AHF. If this had been done, we may have a better idea of the definition of positivity to use for each subset of patients based on their pretest probability. For example, someone who is deemed very unlikely to have AHF (10% or less) may require zero lung zones to rule out AHF, since a neg LR of 0.3 drops the post-test probability to below 5%. Someone who has intermediate probability (50%) may require two positive anterior zones (LR 5.7) or all 8 zones to be positive (LR 9.2) to give a post-test probability of 85-90% or above.

      A quick point about the use of expert chart review for AHF studies, and how this too may lead to problems with defining AHF. Many expert reviewers will implicitly give greater weight to a set of variables, say CXR or BNP, rather than other variables, to come to the diagnosis. We know that these variables have their own limitations, just as the physical exam in diagnosis. I argue that what is truly the gold standard is a transthoracic echocardiogram performed prior to treatment, as well as to monitor response to treatment, because this gives you the sensitive hemodynamic information needed. However, this is logistically impractical because that would mean having 24/7 presence of cardiologists in the ED (and very unhappy cardiologists!).

      What if we were able to train emergency physicians to perform a similar but abbreviated exam pre and post treatment? Would we not be able to diagnose the type and severity of AHF, as well as to monitor response to treatment? And possibly identify low-risk patients that can be safely discharged? Just a thought.

      Thanks again to SGEM and all listeners for sharing our study and for the excellent discussion!

  • SAEM EBM IG

    I
    don’t disagree with anything that Andrew and Mark have stated. As is
    true for most diagnostic “tests” (history, physical exam, labs, and
    imaging), the LR+ and LR- are not sufficient to rule-in or rule-out the
    “disease” (acute CHF in this case) in isolation.
    The benefit of Alan’s work is that we can now quantify just how well we
    can (or can’t) do so with bedside US for CHF using inexperienced
    sonographers.

    The diagnostic accuracy “shift” phenomenon that Andrew & Mark describe
    where bedside US for CHF will improve with more experienced
    sonographers actually has a name. It is called temporal bias and is
    described further on page 56 of http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470657839.html. Interestingly, some diagnostic bias experts
    disagreed that temporal bias is a real issue, which is why it is
    not in this manuscript (http://pmid.us/24238322). However,
    I believe that temporal bias is one of the often unrecognized forms of bias in
    diagnostic research.

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  • TheSGem

    Thrilled to have this episode of #sgemhop make the list of best global FOAMed this week. http://lifeinthefastlane.com/litfl-review-182/

  • Well said. That was quite insightful.
    Newton @ Kenyatta University school of medicine.http://medicine.ku.ac.ke

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