Can we rely on B-line in bedside lung ultrasound to guide our acute management of acute dyspnoea?

Date First Published:
July 11, 2017
Last Updated:
July 12, 2017
Report by:
Dr. Wong Chun Kit, Arthur, Resident in Emergency Medicine (Prince of Wales Hospital, Hong Kong)
Three-Part Question:
In [critically ill patients presenting with acute dyspnoea], is [B-line in lung ultrasound assessment] an important element in [the search for the underlying etiology]?
Clinical Scenario:
75 year-old-gentleman from the old age residential home presented with acute breathlessness since 2 hours ago. He has a background of COPD, IHD, HT and CVA. The patient was too symptomatic to volunteer any history. Only very limited information was obtained from the carer from the residential home. ABG showed type 2 respiratory failure. The portable CXR machine was still on its way. You wonder if any further useful information can be obtained from bedside lung ultrasound assessment to help you quickly decide the treatment plan in the high dependency unit.
Search Strategy:
Keywords used:
‘Lung ultrasound’, ‘Comet tail’, ‘B-line’, ‘B-profile’, ‘Pulmonary edema’, ‘acute respiratory distress syndrome’, ‘Congestive heart failure’
A. MEDLINE using the PubMed interface (1950 – present)
B. Google scholar
C. Cochrane library: no reviews were found on the subject
Search is limited to English language
Outcome:
11 papers were found to be relevant.
Relevant Paper(s):
Study Title Patient Group Study type (level of evidence) Outcomes Key results Study Weaknesses
A lung ultrasound sign allowing bedside distinction between pulmonary edema and COPD: the comet-tail artefact. Lichtenstein et al 1998 France ICU Prospective, observational Screening for the comet-tail artefact arising from the pleural line can help to distinguish between cardiogenic pulmonary edema and exacerbation of COPD. The US test was positive in 100% of patients with pulmonary edema, negative in 92% of patients with COPD, and negative in 98.75% of patients without clinical or radiologic respiratory anomalies. Cases without definite diagnosis were excluded. In addition, non-cardiac causes of interstitial syndrome such as pneumonia, ARDS or chronic interstitial lung diseases also give rise to comet-tail artifacts.
The comet tail artifact had a sensitivity of 100% and a specificity of 92% in the diagnosis of pulmonary edema when compared with COPD.
Ultrasound comet-tail images: ”: A Marker Of Pulmonary Edema: A Comparative Study With Wedge Pressure And Extravascular Lung Water. Agricola E et al 2005 Italy Post cardio-pulmonary bypass surgery Prospective, observational The presence and the number of comet-tail images provide reliable information on interstitial pulmonary edema. Significant positive linear correlations were found between comet score and extravascular lung water (r = 0.42, p = 0.001), between comet score and wedge pressure (r=0.48, p = 0.01), and between comet score and radiologic lung water score (r = 0.60, p = 0.0001). Small study size. Patients with lung diseases were excluded; therefore results may only be applicable to a narrow group of patients.
Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Lichtenstein et al. 2008 France ICU patients with respiratory failure Prospective, observational The B profile characterizes pulmonary edema with high accuracy. Multiple anterior diffuse B lines with lung sliding indicated pulmonary edema (n=64) with 97% sensitivity and 95% specificity. The US operators were not blinded to the patient’s clinical presentation, thus creates potential bias to the interpretation
Ultrasound lung comets for the differential diagnosis of acute cardiogenic dyspnoea: a comparison with natriuretic peptides. Gargani et al. 2008 Italy Cardiopulmonay ward patients Prospective, observational In patients admitted with acute dyspnoea, the accuracy of ULC in predicting the cardiac origin of dyspnoea is high. NT-proBNP values were correlated with the number of ULCs (r= 0.69, p<.0001). The number of patients with non-cardiogenic dyspnoea is small compared to the number of patients with cardiogenic dyspnoea. This difference may influence the accuracy of ULCs, overestimating its specificity.
The presence of 4 ULCs was found to maximize the overall diagnostic accuracy with a sensitivity of 81% and a specificity of 85%.
The presence of 9 ULCs had a sensitivity of 73% and a specificity of 100%.
Chest sonography: a useful tool to differentiate acute cardiogenic pulmonary edema from acute respiratory distress syndrome. Copetti et al. 2008 Italy ICU patients with APE and ARDS Prospective, observational ULC is found in both APE and ARDS, thus cannot be used to differentiate one from the other. Other US features such as pleural line abnormalities, absence or reduction of the ‘gliding sign’, spared areas, consolidations, pleural effusion, and lung pulse are useful for differentiation. ULC: 100% of patients with ARDS and 100% of patients with APE. APE and ARDS groups were divided based on existing clinical criteria. US features in ARDS need validation in future prospective studies.
Emergency thoracic ultrasound in the differentiation of the etiology of shortness of breath (ETUDES): sonographic B-lines and N-terminal pro-BNP in diagnosing congestive heart failure Liteplo et al. 2009 United States ED patients with SOB and in whom NT-ProBNP level was sent Prospective observational Lung US can be used alone or can provide additional predictive power to NT-ProBNP in diagnosing CHF patients. -A positive eight-zone US (defined as at least two positive zones on each side) had a LR+ of 3.88 and a LR− of 0.5. US results may have been altered by treatment (e.g. diuretics) either early in their ED course or in the out-of-hospital setting, decreasing the sensitivity of the test.

Lack of a true criterion standard in diagnosing CHF
For two-zone US, LRs+ was 4.73 when inferior lateral zones were positive bilaterally and LR- was 0.3. These changed to 8.04 and 0.11 respectively, when congruent with NT-ProBNP.
Thoracic ultrasonography: A new method for the work-up of patients with dyspnea. Vitturi et al. 2011 Italy Internal medical ward patients with dyspnoea Prospective observational Lung US is more sensitive than chest radiography and echocardiography in diagnosing HF, and it exhibits sensitivity and specificity similar to that of the NT-pro-BNP assay, but it also offers more rapid changes with the resolution of the clinical picture. The group of patients with positive US findings had a higher frequency of HF diagnoses (X2 92.5, p < 0.005) Patients received non-standardised treatment in emergency department before admission. Forms of treatment (e.g. diuretics) and length of stay in emergency room may affect the findings of lung US to different extent.
Moreover, the decrease in the number of B lines at 48 h was significantly greater (p < 0.005) among patients treated for heart failure.
B lines sensitivity: 0.97; specificity: 0.79
Combination of lung ultrasound and N-terminal pro-BNP in differentiating acute heart failure from COPD and asthma as cause of acute dyspnea in prehospital emergency setting. Prosen et al. 2011 Slovenia Prehospital patients with acute dyspnoea Prospective observational ULC alone or in combination with NT-proBNP has high diagnostic accuracy in differentiating acute HF-related from COPD/asthma-related causes of acute dyspnoea The US comet-tail sign has 100% sensitivity, 95% specificity, 100% NPV and 96% PPV for the diagnosis of HF. Only patients with primary HF or COPD/asthma diagnosed in prehospital settings were included, and this limitation decreases the generalizability of this study to other causes of acute dyspnoea
The combination of US sign and NT-proBNP has 100% sensitivity, 100% specificity, 100% NPV and 100% PPV.
Diagnostic performance of cardiopulmonary ultrasound performed by the emergency physician in the management of acute dyspnea. Gallard et al. 2015 France ED patients with acute dyspnoea Prospective observational B profile in lung US allows one to accurately diagnose acute LVHF in ED setting. Lung US allowed to affirm or deny the presence of B profile with 100% reliability and diagnose acute left sided heart failure with an accuracy of 88% Selection bias: Patient included into the study only when ED physician trained in cardiopulmonary US is available.
Lung Ultrasound-Implemented Diagnosis of Acute Decompensated Heart Failure in the ED: A SIMEU Multicenter Study. Pivetta et al. 2015 Italy ED patients presented with acute dyspnoea Prospective, observational The implementation of lung US with the clinical evaluation may improve accuracy of ADHF diagnosis in patients presenting to the ED. Lung US had a significantly higher accuracy (sensitivity, 97%; specificity, 97.4%) in differentiating ADHF from non-cardiac causes of acute dyspnoea than the initial clinical workup, chest radiography alone, natriuretic peptides Selection bias: Patient were not recruited consecutively, recruitment required presence of ED physicians with expertise in lung US.

Lack of standard diagnostic criteria for the final diagnosis.

ED physicians who performed the US were not blinded to the workup results.
Clinical application of rapid B-line score with lung ultrasonography in differentiating between pulmonary infection and pulmonary infection with acute left ventricular heart failure. Liu et al. 2015 China ED patients with acute dyspnoea Prospective, observational The B-line score in BLUE protocol can help make a rapid differential diagnosis between pulmonary infection and pulmonary infection with acute LVHF. -The B-line score in patients with pulmonary infection with acute LVHF (11.5 ± 1.5) was significantly higher than those with pulmonary infection alone (7.2 ± 1.9) (P = .000). Small sample size
Author Commentary:
Abbreviations:
US = ultrasound
ULC = ultrasound lung comets
ADHF = acute decompensated heart failure
LVHF = Left ventricular heart failure
ARDS = acute respiratory distress syndrome
APE = acute pulmonary edema
COPD = chronic obstructive pulmonary disease
ED = Emergency department

All of the studies included are of prospective and observational in the type of design. No relevant interventional studies or randomised controlled trials were included because the question of this review was focusing on the sensitivity and specificity of B-line as a diagnostic tool, but not on the treatment outcomes.

The B-line is the elementary sign of lung interstitial syndrome. It is defined using seven criteria, three of which are always present: a comet-tail artefact; arising from the pleural line; moving in concert with lung sliding (when lung sliding is present). The other four criteria are almost always present: long; well-defined; erasing A-lines; hyperechoic (Lichtenstein 2017 doi: 10.1183/20734735.004717).

B profile/B lines/comet tail artifacts in lung ultrasound scan are seen more frequently in patients with pulmonary congestion, which is almost a universal finding in patients with acute heart failure. However, B profiles are also seen in other causes of interstitial syndrome such as pneumonia, ARDS or chronic interstitial lung diseases. The identification and validation of other lung ultrasound features in the future may enable better differentiation.

The recent years have seen an increase in the use of combined lung and cardiac ultrasound in the evaluation of patients with acute dyspnoea. Different ultrasound protocols have been developed as a result (e.g. BLUES, FALLS etc.), and their respective sensitivity and specificity in diagnosing the underlying etiology are being studied. Future best evidence topic review can be conducted in this area.
Bottom Line:
B-line in lung ultrasound is highly sensitive and specific for lung interstitial syndrome. In most cases, the presence of which may point towards heart failure as the cause of acute dyspnoea. B-line is also demonstrated to be a superior tool when compared with conventional chest radiograph in the evaluation of the amount of extravascular lung water. Nevertheless, traditional history taking, physical exam and investigations are still important in the identification of the different causes of interstitial syndrome.
References:
  1. Lichtenstein et al. A lung ultrasound sign allowing bedside distinction between pulmonary edema and COPD: the comet-tail artefact.
  2. Agricola E et al. Ultrasound comet-tail images: ”: A Marker Of Pulmonary Edema: A Comparative Study With Wedge Pressure And Extravascular Lung Water.
  3. Lichtenstein et al. . Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol.
  4. Gargani et al. . Ultrasound lung comets for the differential diagnosis of acute cardiogenic dyspnoea: a comparison with natriuretic peptides.
  5. Copetti et al. . Chest sonography: a useful tool to differentiate acute cardiogenic pulmonary edema from acute respiratory distress syndrome.
  6. Liteplo et al.. Emergency thoracic ultrasound in the differentiation of the etiology of shortness of breath (ETUDES): sonographic B-lines and N-terminal pro-BNP in diagnosing congestive heart failure
  7. Vitturi et al.. Thoracic ultrasonography: A new method for the work-up of patients with dyspnea.
  8. Prosen et al. . Combination of lung ultrasound and N-terminal pro-BNP in differentiating acute heart failure from COPD and asthma as cause of acute dyspnea in prehospital emergency setting.
  9. Gallard et al. . Diagnostic performance of cardiopulmonary ultrasound performed by the emergency physician in the management of acute dyspnea.
  10. Pivetta et al. . Lung Ultrasound-Implemented Diagnosis of Acute Decompensated Heart Failure in the ED: A SIMEU Multicenter Study.
  11. Liu et al. . Clinical application of rapid B-line score with lung ultrasonography in differentiating between pulmonary infection and pulmonary infection with acute left ventricular heart failure.