1. Correct Answer: A. A horizontal reverberation artifact that represents air-pleura interface

Rationale: A-lines are horizontal reverberation artifacts that represent a strong reflection from the air-pleura interface. The presence of A-lines is not itself pathologic. The distance between A-lines is equal to the distance from the probe to the air-pleura interface.

1. Doerschug KC, Schmidt GA. Intensive care ultrasound: III. Lung and pleural ultrasound for the intensivist. Ann Am Thorac Soc. 2013;10(6):708-712. doi:10.1513/annalsats.201308-288ot.

2. Lichtenstein DA. BLUE-protocol and FALLS-protocol. Chest. 2015;147(6):1659-1670. doi:10.1378/chest.14-1313.

2. Correct Answer: B. This pattern is commonly seen in patients with dry interlobular septae

Rationale: An A-line predominant pattern, as shown in Figure 56.1, indicates that the interlobular septae are characteristically dry. The A-line reverberation artifact is an apparent “second” pleural reflection, deep to the pleura, twice the distance of the original pleural reflection. It represents a strong reflection from the aeration just below the pleural line, which is consistent with aerated lung, but can also be present with pneumothorax. The presence of B-lines would suggest an interstitial syndrome or edematous interlobular septae (pulmonary edema), which are not seen here. Additionally, in an ICU population of mechanically ventilated patients, an A-line pattern has a 93% specificity, 50% sensitivity, and 97% positive predictive value for a pulmonary artery occlusion pressure (PAOP) ≤18 mm Hg. However, in a later study, lung ultrasound was shown to be of limited usefulness for predicting PAOP.

1. Lichtenstein DA. BLUE-protocol and FALLS-protocol. Chest. 2015;147(6):1659-1670. doi:10.1378/chest.14-1313.

2. Lichtenstein DA, Mezière GA, Lagoueyte J-F, Biderman P, Goldstein I, Gepner A. A-lines and B-lines: lung ultrasound as a bedside tool for predicting pulmonary artery occlusion pressure in the critically ill. Chest. 2009;136(4):1014-1020, ISSN 0012-3692, doi:10.1378/chest.09-0001.

3. Volpicelli G, Skurzak S, Boero E, et al. Lung ultrasound predicts well extravascular lung water but is of limited usefulness in the prediction of wedge pressure. Anesthesiology. 2014;121(2):320-327.

3. Correct Answer: B. Low gain, probe at a perpendicular axis to the surface of the skin

Rationale: A-lines and lung sliding are best visualized with the linear or phased array transducers, but the phased array probe may be needed to achieve the depth adequate to visualize A-lines. The linear transducer allows for high-frequency detailed visualization of the pleural line. Proper positioning of the probe perpendicular to the skin with a low gain setting will optimize these artifacts.

1. Doerschug KC, Schmidt GA. Intensive care ultrasound: III. Lung and pleural ultrasound for the intensivist. Ann Am Thorac Soc. 2013;10(6):708-712. doi:10.1513/annalsats.201308-288ot.

4. Correct Answer: A. Profuse B-lines are present and consistent with an interstitial syndrome.

Rationale: B-lines are vertical reverberation artifacts commonly seen in patients with interstitial syndromes. In this case, the patient appears to have signs and symptoms consistent with heart failure. On ultrasound, an occasional B-line may be a normal finding between rib spaces, but this patients has many B-lines (more than three) in a single image, which is abnormal. A thin pleural line and profuse B-lines in a symmetric distribution are highly suggestive of an interstitial syndrome (e.g., pulmonary edema). Evidence also suggests that if many B-lines are detected in a bilateral, symmetric distribution in all lung zones, this is associated with increased left ventricular filling pressure.

1. Hubert A, Girerd N, Breton HL, et al. Diagnostic accuracy of lung ultrasound for identification of elevated left ventricular filling pressure. Arch Cardiovasc Dis. 2019;11(1):53. doi:10.1016/j.acvdsp.2018.10.115.

2. Lichtenstein DA. BLUE-protocol and FALLS-protocol. Chest. 2015;147(6):1659-1670. doi:10.1378/chest.14-1313.

3. Muniz RT, Mesquita ET, Souza Junior CV, Martins WA. Pulmonary ultrasound in patients with heart failure—systematic review. Arq Bras Cardiol. 2018;110(6):577-584. doi:10.5935/abc.20180097.

5. Correct Answer: D. I, III, and IV

Rationale: Lichtenstein describes three mandatory criteria used to identify B-lines: a comet-tail (reverberation) artifact, arising from the pleural line, which moves in concert with lung sliding when present. Four other criteria are often seen with B-lines: extend from pleural line to the distal edge of the image, well-defined, erases A-lines, hyperechoic. These criteria help to distinguish B-lines from other comet-tail artifacts.

1. Lichtenstein D. Novel approaches to ultrasonography of the lung and pleural space: where are we now? Breathe. 2017;13(2):100-111. doi:10.1183/20734735.004717.

2. Miller A. Practical approach to lung ultrasound. BJA Educ. 2016;16(2):39-45. doi:10.1093/bjaceaccp/mkv012.

6. Correct Answer: C. Heart failure exacerbation

Rationale: Pulmonary edema can develop rapidly in patients with mitral regurgitation from a myocardial infarction or acute heart failure. In this instance, B-lines help to confirm the diagnosis of pulmonary edema as the cause for impending respiratory failure. A systematic review and meta-analysis of ED patients with acute heart failure suggests that point-of-care lung ultrasound can be used accurately and reliably as an adjunct to other diagnostic modalities.

1. Lichtenstein DA. BLUE-protocol and FALLS-protocol. Chest. 2015;147(6):1659-1670. doi:10.1378/chest.14-1313.

2. Mcgivery K, Atkinson P, Lewis D, et al. Emergency department ultrasound for the detection of B-lines in the early diagnosis of acute decompensated heart failure: a systematic review and meta-analysis. CJEM. 2018;20(3):343-352. doi:10.1017/cem.2018.27.

7. Correct Answer: C. A/B Pattern

Rationale: In this scenario, the patient presents with the clinical syndrome of pneumonia associated with focal B-lines on lung ultrasound. Figure 56.3A demonstrates B-lines and the pleura appears somewhat irregular, which is consistent with an inflammatory interstitial syndrome. In contrast, Figure 56.3B demonstrates normal pleura with an A-line pattern. An A/B pattern describes an A-profile (normal appearance) in one hemithorax and a B-profile (B-lines) in the other. This suggests a heterogeneous distribution of the inflammatory process, as may be seen with pneumonia, in contrast to a diffuse pattern, which would be expected with cardiogenic pulmonary edema.

1. Bhatt H, Patel C, Parikh S, Jhaveri B, Puranik J. Bedside lung ultrasound in emergency protocol as a diagnostic tool in patients of acute respiratory distress presenting to emergency department. J Emerg Trauma Shock. 2018;11(2):125. doi:10.4103/jets.jets_21_17.

2. Lichtenstein DA, Mezière GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure*: the BLUE protocol. Chest. 2008;134(1):117-125. doi:10.1378/chest.07-2800.

8. Correct Answer: A. Shred sign

Rationale: Figure 56.4 demonstrates a shred sign. The shred sign artifact is seen when there is subpleural consolidation of lung tissue, in which a portion of consolidated lung is visualized adjacent to the reflection from a deeper, aerated portion of lung. The irregular interface between the consolidated and aerated lung tissues gives a “shredded” appearance. The shred sign is nonspecific, but can help to define lung pathology in a clinical context. For example, in the case presented in Questions 7 and 8, this likely represents ultrasound evidence of pneumonia. It should be noted that the shred sign can also be seen with pulmonary infarct, subpleural lung abscess, and lung cancer.

1. Biswas A, Lascano JE, Mehta HJ, Faruqi I. The utility of the “shred sign” in the diagnosis of acute respiratory distress syndrome resulting from multifocal pneumonia. Am J Respir Crit Care Med, 2017;195(2). doi:10.1164/rccm.201608-1671im.

2. Mojoli F, Bouhemad B, Mongodi S, Lichtenstein D. Lung ultrasound for critically ill patients. Am J Respir Crit Care Med. 2019;199(6):701-714. doi:10.1164/rccm.201802-0236ci.

3. Rinaldi L, Milione S, Fascione MC, et al. Relevance of lung ultrasound in the diagnostic algorithm of respiratory diseases in a real-life setting: a multicentre prospective study. Respirology. 2019. doi:10.1111/resp.13659.

9. Correct Answer: A. Community-acquired pneumonia

Rationale/Critique: The case presented in Questions 7, 8, and 9 and chest ultrasound findings (Figures 56.3 and 56.4) suggest a focal inflammatory or infectious process, such as community-acquired pneumonia. ARDS would demonstrate a patchy pattern of B-lines with hypoxia, which would be bilateral. Hydrostatic pulmonary edema from a heart failure exacerbation would show a thickened pleural line with many B-lines bilaterally. Chest ultrasound examination of those with COPD and asthma can be normal (A-line pattern) and would also be expected to appear symmetric.

1. Lichtenstein DA. BLUE-protocol and FALLS-protocol. Chest. 2015;147(6):1659-1670. doi:10.1378/chest.14-1313.

10. Correct Answer: A. Acute respiratory distress syndrome

Rationale: Figure 56.5 and Videos 56.3A and B demonstrate a bilateral heterogeneous distribution of B-lines. In the figure, the left upper lobe is spared. The left lower lobe, right upper lobe, and right lower lobe with B-lines are shown. The right posterolateral aspect has a pleural effusion and left appears normal. This distribution is consistent with ARDS. Pulmonary edema is a profuse pattern of B-lines with intact lung sliding. Pulmonary embolism with infarct would demonstrate A-line pattern, with or without shred sign, and pleural effusion. Asthma exacerbation would also demonstrate an A-line predominant pattern.

1. Copetti R, Soldati G, Copetti P. Chest sonography: a useful tool to differentiate acute cardiogenic pulmonary edema from acute respiratory distress syndrome. Cardiovasc Ultrasound. 2008;6(1). doi:10.1186/1476-7120-6-16.

2. Doerschug KC, Schmidt GA. Intensive care ultrasound: III. Lung and pleural ultrasound for the intensivist. Ann Am Thorac Soc. 2013;10(6):708-712. doi:10.1513/annalsats.201308-288ot.

11. Correct Answer: A. The presence of B-lines rules out pneumothorax.

Rationale: ARDS is a heterogeneous disease process that can produce a B-line predominant pattern in a heterogeneous distribution. With high-pressure ventilation, pneumothorax can develop. However, the presence of B-lines rules out pneumothorax with 100% sensitivity and 100% negative predictive value, because two opposing layers of pleura must be present to create this artifact. In addition, the number of B-lines may have a prognostic impact on ARDS mortality and the likelihood of successfully weaning from a ventilator. The asymmetric heterogeneous B-line pattern argues against cardiogenic pulmonary edema.