Acute dyspnea represents one of the most frequent and diagnostically challenging complaints in emergency medicine, accounting for nearly 30% of all emergency department (ED) visits worldwide [1]. The underlying etiologies can range from cardiac causes such as acute decompensated heart failure (ADHF) to pulmonary conditions such as pneumonia, chronic obstructive pulmonary disease (COPD) exacerbations, and acute respiratory distress syndrome (ARDS). Timely differentiation between cardiac and pulmonary causes is essential, as the therapeutic approaches differ significantly. Cardiac dyspnea often responds to diuretics and vasodilators, whereas pulmonary causes require antimicrobials, bronchodilators, or ventilatory support.

Traditional diagnostic modalities, including chest radiography, computed tomography (CT), and natriuretic peptide assays (BNP/NT-proBNP), have well-documented limitations. Chest X-rays lack sensitivity in early interstitial edema, CT scans are costly and time-consuming, and BNP levels can be confounded by renal impairment, obesity, and advanced age [2]. In this context, lung ultrasound (LUS) has emerged as a valuable, non-invasive, and bedside diagnostic tool that allows real-time differentiation of dyspnea causes without radiation exposure [3]. LUS detects characteristic vertical reverberation artifacts termed B-lines, which arise from the pleural line and extend to the bottom of the screen without fading. The number, distribution, and symmetry of these B-lines can differentiate cardiogenic pulmonary edema (diffuse, symmetric) from pulmonary pathology (focal, asymmetric) [4,5]. This study was designed to assess the diagnostic performance of B-line assessment in LUS for differentiating cardiac and pulmonary causes of acute dyspnea in an Indian emergency department setting.

AIMS

The primary aim of this study was to evaluate the diagnostic accuracy and clinical utility of B-lines in lung ultrasound for differentiating cardiac and pulmonary causes of acute dyspnea in adult patients presenting to the emergency department.

OBJECTIVES

1. To determine the diagnostic sensitivity, specificity, and predictive values of B-lines in differentiating cardiac and pulmonary etiologies of acute dyspnea.
   2. To analyze B-line distribution, symmetry, and associated pleural characteristics that improve diagnostic specificity.
   3. To compare the diagnostic performance of LUS with traditional imaging modalities such as chest X-ray and computed tomography.
   4. To evaluate the feasibility of incorporating B-line assessment into emergency workflows for rapid bedside diagnosis.

Study Design and Setting: A prospective observational study was conducted in the Emergency Department of Sri Siddhartha Medical College & Research Center, Tumakuru, Karnataka, India, over a two-month period (May–June 2025). Ethical approval was obtained from the institutional ethics committee, and informed consent was secured from all participants.

Study Population: A total of 60 adult patients (>18 years) presenting with acute dyspnea were enrolled. Exclusion criteria included trauma-related dyspnea, pre-existing chronic interstitial lung disease, and refusal to undergo LUS.

Data Collection and Ultrasound Protocol: Patient enrollment and baseline data collection. Consecutive adult patients presenting to the ED with acute dyspnea were screened for eligibility. After confirming inclusion and exclusion criteria, written informed consent was obtained. For each enrolled patient we recorded: demographic data (age, sex), comorbidities (hypertension, diabetes, coronary artery disease, chronic lung disease), medication history, time of symptom onset, and triage category. At presentation, the following clinical data were captured: heart rate, blood pressure, respiratory rate, peripheral oxygen saturation (SpO₂) on room air or supplemental oxygen, temperature, and Glasgow Coma Scale when applicable. Initial laboratory values (complete blood count, serum electrolytes, renal function, arterial blood gas if performed, and BNP/NT-proBNPwhere available) and chest radiograph/CT results (if obtained as part of clinical care) were recorded and time-stamped to enable comparison with LUS timing.

Timing and blinding. Lung ultrasound was performed as early as possible and within one hour of ED presentation in all patients to minimize temporal variation. Ultrasound operators were blinded to the final adjudicated diagnosis at the time of scanning. Treating clinicians were blinded to study-specific LUS interpretation summaries (operators reported only clinically actionable findings when necessary), and final diagnoses were made by an independent adjudication committee that reviewed the full clinical course, laboratory results, imaging (radiograph/CT), microbiology, and response to therapy.

Operators, training and quality assurance. Scans were performed by emergency physicians credentialed in point-of-care ultrasound who had completed a standardized training program (minimum 20 supervised LUS examinations and completion of a structured didactic curriculum). To assess inter-observer reliability, a subset (20%) of scans was independently reviewed by a second blinded operator. Periodic quality assurance sessions (weekly) were held during the study period to review stored clips and harmonize interpretation criteria.

Equipment and machine settings. All examinations used portable ultrasound machines (make/model) equipped with a phased-array (2–5 MHz) and curvilinear (3–5 MHz) probe. Default lung presets were used with the following modifications when necessary: depth set to visualize pleura and at least 4–6 cm of underlying lung tissue, total gain adjusted to minimize background noise while preserving artifact visualization, and harmonics switched off to optimize artifact detection. All clips were recorded at minimum 6–10 seconds per scanning window and saved in DICOM or native machine format for offline review.

Scanning protocol and patient positioning. A standardized 8-zone approach was used for hemodynamically unstable or uncooperative patients (anterior and lateral zones bilaterally), while a 12-zone protocol (anterior, lateral and posterior zones bilaterally) was used when patient condition permitted. Scanning positions were: anterior (parasternal to anterior axillary line, second to fourth intercostal spaces), lateral (mid-axillary to posterior axillary line), and posterior (scapular line to paravertebral region) when accessible. Patients were scanned in the supine or semi-recumbent position when necessary; seated or upright positioning was used for posterior zones when clinically feasible.

Image acquisition technique. The probe was placed perpendicular to the ribs in an intercostal space, with the marker oriented cephalad. For each zone we recorded cine clips and still images. Operators used slow, deliberate sweeps and held still for at least one respiratory cycle per clip to assess pleural motion. Probe pressure was minimized to avoid compressive artifacts. When pleural effusion was suspected, the probe was angulated and the liver/spleen used as acoustic windows to confirm anechoic collections and measure maximal vertical depth.

Interpretation criteria and measurement. A B-line was defined as a discrete, vertical, laser-like, hyperechoic reverberation artifact that arose from the pleural line, moved with lung sliding and extended to the bottom of the screen without fading. A zone was considered pathological if ≥3 B-lines were present. We recorded: number of B-lines per zone (count), distribution (focal vs. diffuse; unilateral vs. bilateral), pleural line appearance (smooth vs. irregular), presence/absence of lung sliding, subpleural consolidations, and pleural effusions (presence and maximal depth in cm). The B-profile was defined as diffuse bilateral multiple B-lines with preserved sliding; the B′-profile as focal or asymmetric B-lines often with pleural irregularity and reduced/absent sliding.

Data recording and storage. All findings were entered into a standardized electronic case report form with time stamps linking ultrasound images to clinical events. Raw image and cine files were archived securely for audit and blinded review. A random sample of 10–20% of examinations was re-reviewed offline to determine intra- and inter-observer agreement using Cohen’s kappa and intraclass correlation coefficients for B-line counts.

Measures to reduce bias. To limit verification bias, final diagnosis adjudication used complete clinical data and, where possible, imaging/biomarker confirmation independent of the LUS operator’s interpretation. Operators were not involved in adjudication. Predefined, objective LUS criteria were used to minimize subjective variability. Statistical analyses adjusted for potential confounders (age, comorbidities) and sensitivity analyses were performed excluding patients with mixed or indeterminate diagnoses.

Statistical Analysis: Data were analyzed using SPSS version 26.0. Continuous variables were expressed as mean ± standard deviation (SD) and categorical variables as frequencies and percentages. Diagnostic performance metrics (sensitivity, specificity, PPV, NPV, LR+, LR−) were calculated, and comparisons with chest X-ray were made using Chi-square and t-tests, with a significance threshold of p < 0.05.

A total of 60 patients were included, comprising 33 males (55%) and 27 females (45%), with a mean age of 68.5 ± 12.3 years. Thirty-six patients (60%) had cardiac causes (ADHF) and twenty-four (40%) had pulmonary causes (pneumonia or ARDS). Baseline demographics and clinical parameters are shown in Table 1.

Table 1: Baseline demographic and clinical characteristics of patients.

Ultrasound findings showed distinct differences in B-line profiles between cardiac and pulmonary etiologies (Table 2).

Table 2: Comparison of ultrasound findings between cardiac and pulmonary groups

The findings of this study underscore the pivotal role of lung ultrasound (LUS) as a frontline diagnostic tool in the evaluation of patients presenting with acute dyspnea. The strong correlation between specific B-line profiles and underlying etiology—namely, the B-profile (bilateral, symmetric B-lines with lung sliding) in cardiogenic pulmonary edema and the B′-profile (asymmetric or focal B-lines without sliding) in pulmonary pathology—demonstrates that pattern recognition on ultrasound can yield diagnostic accuracy comparable to, and often superior to, conventional imaging modalities such as chest radiography and computed tomography (CT).

In our cohort, LUS achieved a sensitivity of 90% and a specificity of 85%, aligning closely with previous multicenter trials and meta-analyses. For instance, Pivetta et al. (2015) reported sensitivity and specificity values of 88% and 86%, respectively, in a multicenter SIMEU study, while Al Deeb et al. (2014) demonstrated pooled estimates of 94% sensitivity and 92% specificity in their meta-analysis of point-of-care ultrasonography for acute cardiogenic pulmonary edema. The concordance between our results and international evidence reinforces the reproducibility and reliability of B-line assessment across diverse clinical settings and operator experience levels.

Pathophysiological Correlation

From a pathophysiological standpoint, B-lines represent vertical, hyperechoic reverberation artifacts originating from the pleural line, corresponding to interlobular septa caused by increased extravascular lung water. In cardiogenic pulmonary edema, the interstitial fluid accumulates symmetrically due to elevated hydrostatic pressures, producing diffuse, bilateral B-lines with preserved pleural sliding. Conversely, non-cardiogenic pulmonary conditions such as pneumonia or acute respiratory distress syndrome (ARDS) result in localized alveolar and interstitial inflammation, leading to asymmetric B-lines, often accompanied by pleural irregularity or subpleural consolidations. This mechanistic distinction underpins the diagnostic specificity of LUS in differentiating cardiac from pulmonary causes of dyspnea.

Our study supports this interpretation, demonstrating significantly higher mean B-lines per lung zone and a greater frequency of bilateral distribution in patients with cardiac etiology (p < 0.001). In contrast, pleural irregularity and subpleural consolidation were far more common in pulmonary etiologies (p < 0.001), emphasizing the diagnostic value of integrating qualitative pleural assessment with quantitative B-line counting.

Comparison with Traditional Diagnostic Modalities
Traditional imaging modalities, though widely used, are limited in both sensitivity and practicality in the emergency setting. Chest radiography, for example, often fails to detect early interstitial edema and provides only a static snapshot that can lag behind clinical status. Computed tomography (CT) remains the gold standard for certain pulmonary pathologies but is time-consuming, expensive, and exposes patients to ionizing radiation—factors that limit its use for immediate bedside decision-making. In contrast, LUS offers dynamic thickened, real-time imaging that can be performed rapidly at the bedside, even in hemodynamically unstable patients.

Moreover, LUS can be repeated serially to monitor therapeutic response, such as the reduction of B-lines following diuretic administration in heart failure patients. This capacity for continuous, radiation-free monitoring enhances both diagnostic and prognostic value—features unmatched by chest radiography or CT.

Comparison with Existing Literature: The diagnostic accuracy and rapidity of LUS have been extensively validated. Volpicelli et al. (2012) and Lichtenstein et al. (2008), through the BLUE protocol, demonstrated that LUS can accurately differentiate between major causes of respiratory failure, including heart failure, pneumonia, COPD, and pulmonary embolism. Maw et al. (2019), in a JAMA Network Open meta-analysis, confirmed that LUS outperforms chest radiography in identifying acute pulmonary edema, with a diagnostic odds ratio nearly twice as high.

Our findings are consistent with these data, reinforcing the notion that LUS should be viewed not as a supplementary test but as a first-line diagnostic modality in acute dyspnea. The reproducibility of diagnostic metrics across various geographic regions, including resource-limited settings like ours, underscores the global applicability of LUS when supported by structured training and standardized interpretation criteria.

Limitations and Study Design Considerations

The study was limited by its small sample size and single-center design, which may restrict external validity. Operator dependency of ultrasound poses another limitation, emphasizing the need for standardized POCUS training. Further, CT correlation was performed only in hemodynamically stable patients, potentially introducing verification bias. Future studies should address these methodological constraints by including multicentric data and inter-observer variability assessments.

Clinical Implications and Future Directions

LUS provides emergency physicians with a rapid, reliable diagnostic modality for acute dyspnea evaluation. Incorporation of B-line assessment into routine ED workflows can reduce unnecessary imaging, accelerate clinical decision-making, and improve patient outcomes. Training emergency clinicians in standardized LUS interpretation will further enhance diagnostic accuracy and confidence.

Future Research Should Focus On

1. Conducting multicentric, randomized controlled studies to validate diagnostic thresholds across diverse populations.
   2. Exploring artificial intelligence–based LUS interpretation to reduce inter-operator variability.
   3. Investigating longitudinal LUS monitoring to assess therapeutic response and predict clinical outcomes such as readmission and mortality.
   4. Developing standardized educational curricula for POCUS training in emergency and critical care settings.

Lung ultrasound (LUS) has emerged as a transformative diagnostic tool in emergency medicine, capable of bridging the gap between rapid bedside assessment and high diagnostic precision. This study demonstrated that B-line assessment using LUS can effectively differentiate between cardiac and pulmonary causes of acute dyspnea with high sensitivity (90%) and specificity (85%). The identification of characteristic B-line patterns — particularly the bilateral, symmetric B-profile in cardiogenic pulmonary edema and the focal, asymmetric B′-profile in pulmonary pathology — underscores the importance of recognizing specific sonographic features rather than relying solely on their presence or absence.

Beyond its diagnostic accuracy, LUS offers profound practical advantages. It is portable, repeatable, free of radiation, and can be performed rapidly at the bedside, making it especially valuable in overcrowded or resource-limited emergency settings. Compared with chest radiography, LUS not only reduces time to diagnosis but also enables dynamic monitoring of patient response to therapy. The ability to detect subtle interstitial changes early can lead to prompt initiation of targeted treatment, improved triage efficiency, and potentially lower morbidity and mortality rates.

Integrating LUS into standard emergency department workflows should be viewed as a necessary evolution in acute care practice rather than an optional adjunct. Routine incorporation of point-of-care LUS for dyspnea evaluation will empower clinicians to make faster, evidence-based decisions, minimize dependence on advanced imaging, and enhance patient throughput and safety. Furthermore, structured training programs and standardized interpretation protocols are essential to ensure consistent results across practitioners and healthcare systems.

In conclusion, B-line lung ultrasound represents a paradigm shift in the diagnostic evaluation of acute dyspnea. Its rapidity, precision, and clinical applicability make it an indispensable tool for modern emergency medicine. Wider adoption and continued research will not only refine its diagnostic thresholds but also consolidate its role as a frontline imaging modality in the global effort to improve outcomes for patients presenting with acute respiratory distress.

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