Clinical Progress Note: Point-of-Care Ultrasound in the Evaluation of the Dyspneic Adult

There are several different sonographic findings that can indicate pneumonia, such as consolidation or “hepatization”, the “shred” sign of an irregular border between consolidated lung and aerated lung, unilateral B-lines, and dynamic air bronchograms. Several recent systematic reviews and meta-analyses have investigated the operating characteristics of POCUS for the diagnosis of pneumonia. These reviews are limited by heterogeneity with respect to different patient populations, sonographers, and reference standards, but all three reviews found similar results, with the pooled AUC values ranging from 95% to 98%.^7-9 This recent evidence along with other reviews suggests that lung ultrasound can serve as a primary diagnostic tool in pneumonia and is probably superior to chest radiography.

Pleural effusions are observed with POCUS as anechoic or hypoechoic areas, generally in dependent lung zones. POCUS may provide additional benefit by better characterizing the effusion as having septations or floating fibrin strands. One recent systematic review and meta-analysis including 1,554 patients found that POCUS had excellent sensitivity and specificity (94% and 98%, respectively) in detecting pleural effusion versus chest radiography (51% and 91%, respectively), both compared with reference standard imaging such as computed tomography. The subgroup analysis found that sensitivity was higher for scanners who were intensivists or radiologists than for other physicians (97% vs 90%; P ≤ .001) and also found a nonstatistically significant trend toward reduced sensitivity when pocket-sized devices were used (90% vs 95%, P = .09).¹⁰

It is extremely important to recognize that a POCUS finding of decreased left ventricular ejection fraction is not synonymous with a diagnosis of ADHF. Bedside providers can use POCUS to estimate cardiac function, but other clinical information is required to determine whether the syndrome of ADHF is present. In one study, examinations performed by 10 internists with approximately 18 hours of training in focused cardiac POCUS had a sensitivity and a specificity of 91% and 88%, respectively, for classifying left ventricular systolic function as normal or mildly, moderately, or severely depressed with “good/substantial” agreement (k = 0.77) compared with formal echocardiography.¹¹ The presence of bilateral B-lines as a sign of pulmonary edema suggests accompanying functional decompensation. A meta-analysis of seven articles including 1075 patients in various clinical settings (ED, ICU, and inpatient wards) found a sensitivity of 94.1% and a specificity of 92.4% for using B-lines to diagnose acute cardiogenic pulmonary edema compared with the final clinical diagnosis.¹² Al Deeb et al. examined 226 patients and found similar sensitivity (95.3%) and specificity (88.2%) for diagnosing acute cardiogenic pulmonary edema when nurses were trained to evaluate for bilateral B-lines in dyspneic patients admitted to the hospital, also compared with the adjudicated final diagnosis.¹³ Carlino et al. evaluated dyspneic patients using a three-minute pocket-sized device scan of the heart, lungs, and inferior vena cava and found that no single view offered a substantial improvement in diagnostic accuracy; however, the combination of bilateral B-lines and/or pleural effusion and either a dilated left atrium or left ventricular ejection fraction (LVEF) of <40% had a very high diagnostic accuracy (AUC 0.97).¹⁴ Russell et al. performed a secondary analysis of a prospective observational study of patients with dyspnea and found that a simple three-view scanning protocol looking for the presence of B-lines on the right and left anterior superior lung zones and an LVEF of <45% took an average of one minute and 32 seconds to perform and had 100% specificity for ADHF if all three were positive.¹⁵ Another recent systematic review and meta-analysis of six studies and 1,827 patients found a sensitivity of 88% (CI 75%-95%) for lung POCUS compared with a chest radiography at a sensitivity of 73% (70%-76%) for the diagnosis of ADHF.¹⁶ All these studies suggest that improving the diagnosis of ADHF does not require complex echocardiographic views and is probably more feasible and accessible than many expect.