1. Correct Answer: C. Right bronchial obstruction

Rationale: When suspecting a PTX, the three most useful findings to look for are: 1) lung sliding; 2) lung pulse; and 3) presence of vertical artifacts. In the case of a PTX, visceral and parietal pleura are separated by intrapleural air, causing complete reflection and attenuation of ultrasound waves at the level of the parietal pleura. Thus, when PTX is present, all three of the aforementioned pulmonary ultrasound findings are not detectable by surface ultrasound. Absence of lung sliding alone has very poor specificity for PTX, with a positive predictive value of only 22%. On the contrary, the identification of even one of these findings is sufficient to rule out PTX in the insonated area (Figure 52.5), making LUS an excellent technique to “rule out” but not necessarily “rule in” PTX.

In Video 52.1B, both lung sliding and pulse can be identified, immediately ruling out PTX on the left side. In Video 52.1A, lung sliding is absent, but lung pulse can still be identified, ruling out PTX also on the right side. Pleural effusion, defined as an anechoic collection between the parietal and visceral pleura, is not demonstrated in Video 52.1A; therefore, right hemothorax is not the correct answer, although we cannot exclude presence of hemothorax in this patient; such a determination would require the scanning of more dependent areas of the pleural cavity. Finally, lung contusion cannot be confirmed in these videos as neither B-lines nor lung consolidations are detected. The most likely correct answer in this case is therefore right bronchial obstruction. Lack of sliding in this case was caused by lack of ventilation related to left mainstem endobronchial intubation. Since the visceral and parietal pleura are still in physical contact, lung pulse (i.e., ultrasonographic detection of transmission of cardiac contraction through lung tissue) is still present.

1. Goffi A, Kruisselbrink R, Volpicelli, G. The sound of air: point-of-care lung ultrasound in perioperative medicine. Can J Anesth. 2018;65(4):399-416.

2. Lichtenstein DA, Menu Y. A bedside ultrasound sign ruling out pneumothorax in the critically III: lung sliding. Chest. 1995;108(5):1345-1348.

3. Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med. 2010;37(2):224-232.

4. Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012;38(4):577-591.

2. Correct Answer: E. None of the above

Rationale: Video 52.2 demonstrates the sonographic appearance of subcutaneous emphysema. The linear hyperechoic artifacts (white arrow, Figure 52.6) do not originate from the pleural line, but within the subcutaneous tissues, above the parietal pleura, as demonstrated by the red arrows in Figure 52.6, where costal cartilage and underlying pleural line can be observed. These artifacts are generated by the high acoustic impedance difference created by the interface between subcutaneous tissues and air bubbles. Sometimes, they can also produce vertical reverberation artifacts (also known as “E-lines”) that can be mistakenly interpreted as B-lines. The key aspect in differentiating E-lines from B-lines is the fact that the first ones do not originate from the pleural line. A “false pleural sliding” can sometimes be observed, generated by the contraction of respiratory muscles during inspiration. Although PTX cannot be diagnosed with certainty, identification of subcutaneous emphysema in this specific context (chest trauma) is highly suspicious for presence of PTX.

Presence of subcutaneous emphysema can significantly affect LUS acquisition and performance; air in the subcutaneous tissues acts as a barrier for the ultrasounds and therefore the pleura cannot be reached. As the pleural line cannot be insonated at this level, no information can be provided on lung sliding and pulse, presence of vertical artifacts originating from the pleural line, and/or collection of fluid in the pleural cavity. For example, no useful information regarding the lung parenchyma can be inferred solely on the basis of Video 52.2 provided. In our patient, the ultrasound transducer was moved inferiorly, in an intercostal space not affected by subcutaneous emphysema, and the image acquired ( Video 52.8A) demonstrated lack of sliding, pulse, and vertical artifacts, supporting the likely diagnosis of traumatic PTX (Figure 52.1). Video 52.8B, acquired on the right hemithorax, demonstrates normal lung findings (lung sliding, lung pulse, and short vertical artifacts).

1. Chiappetta M, Meacci E, Cesario A, et al. Postoperative chest ultrasound findings and effectiveness after thoracic surgery: a pilot study. Ultrasound Med. Biol. 2018;44(9):1960-1967.

2. Goffi A, Kruisselbrink R, Volpicelli, G. The sound of air: point-of-care lung ultrasound in perioperative medicine. Can J Anesth. 2018;65(4):399-416.

3. Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med. 2010;37(2):224-232.

3. Correct Answer: B. LUS is more sensitive but equally specific to CXR for detection of PTX.

Rationale: In the hands of a trained operator and in patients with a high pretest probability (e.g., dyspnea or chest pain posttrauma or central line insertion), LUS is overall more accurate than CXR for the detection of a PTX. In particular, the sensitivity of LUS is higher than supine CXR (79%-91% versus 40%-52%, respectively) (Answers C and D are incorrect), whereas specificity is equally very high for both (98%-99% versus 99%-100%, respectively) (Answer A is incorrect, B is correct). However, as most studies on the diagnostic accuracy of LUS for PTX are in trauma or postprocedural patients, these numbers may overestimate LUS performance in other settings (e.g., nontrauma patients with preexisting conditions such as emphysema).

1. Alrajab S, Youssef A, Akkus N, Caldito G. Pleural ultrasonography versus chest radiography for the diagnosis of pneumothorax: review of the literature and meta-analysis. Crit Care. 2013;17(5):R208.

2. Alrajhi K, Woo MY, Vaillancourt C. Test characteristics of ultrasonography for the detection of pneumothorax: a systematic review and meta-analysis. Chest. 2012;141(3):703-708.

3. Ding W, Shen Y, Yang J, He X, Zhang M. Diagnosis of pneumothorax by radiography and ultrasonography: a meta-analysis. Chest. 2011;140(4):859-866.

4. Correct Answer: A. Video 52.3A demonstrates a lung point, a highly specific finding for PTX

Rationale: Although highly suspicious, the absence of lung sliding, lung pulse, and vertical artifacts is not sufficient to diagnose PTX with certainty. Certain lung conditions (e.g., severe chronic obstructive pulmonary disease, bullous disease, lung overdistension) can create a similar sonographic pattern. Observation of a “lung point,” where the pleural layers meet adjacent to the edge of the PTX, confirms the presence of PTX (red arrow, Figure 52.7).

As observed in Video 52.3A, the respiratory (sliding) and oscillatory (pulse) patterns are visualized on the left side of the screen and intermittently replace the motionless pleura, representing a “lung point,” a “positive” finding with a high specificity but low sensitivity (Answer A is correct, Answer B is incorrect). This “replacement movement” allows differentiation between a true lung point (i.e., confirmation of PTX) and the transition between ventilating and nonventilating areas as they can be observed in patients with pleural adhesions. The presence of a lung pulse excludes PTX. Video 52.3B does show a lung pulse, a finding not seen in PTX (Answers C, D are incorrect).

A lung point cannot be visualized in a larger PTX, where the pleural layers are separated completely, because the “edge” of the PTX is not in an area accessible by ultrasound. In other cases, the lung point may not be visible as it can be hidden behind osseous structures (ribs and scapula). In stable patients, the absence of a lung point does not allow definitive PTX diagnosis and should prompt further investigations (e.g., chest radiography or computed tomography). Finally, although precise quantification of PTX is not possible with LUS, the more laterally the lung point is detected, the greater is the extension of the PTX.

1. Goffi A, Kruisselbrink R, Volpicelli, G. The sound of air: point-of-care lung ultrasound in perioperative medicine. Can J Anesth. 2018;65(4):399-416.

2. Volpicelli G. A lung point that is not a lung point. Intensive Care Med. 2019;45(9):1326-1326.

3. Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med. 2010;37(2):224-232.

4. Volpicelli G, Boero E, Sverzellati N, et al. Semi-quantification of pneumothorax volume by lung ultrasound. Intensive Care Med. 2014;40(10):1460-1467.

5. Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012;38(4):577-591.

5. Correct Answer: D. Likely, neither lung sliding nor pulse is detected

Rationale: In Video 52.4, no sliding or vertical artifacts are seen originating from the pleural line. The “focal” pulsatility observed is generated by the arterial pulsation of the intercostal artery seen immediately about the parietal pleural and not by the transmission of cardiac contractions through the lung parenchyma. Therefore, this video is suspicious for the presence of PTX; in this patient, a lateral movement of the transducer identified a lung point confirming the diagnosis of traumatic PTX.

Several pitfalls have been described in acquisition and interpretation of LUS images in the context of possible PTX, leading to both false-positive and false-negative results. False-negative results can be caused by: 1) failure to insonate the least dependent zone of the chest (typically when scanning a patient in a sitting or semi-recumbent position); 2) misinterpretation of the absence of lung point as a sign of no PTX instead of complete PTX; 3) misinterpretation of vertical artifacts originating in the subcutaneous tissues (E-lines) as vertical artifacts originating from the pleural line (see question 2); 4) presence of loculated PTX; 5) small left PTX at the level of the paracardiac area; 6) misinterpretation of intercostal or internal thoracic artery pulsations as lung pulse; and/or 7) failure to identify lung pulse in the context of severe bradycardia and hypotension. On the contrary, false-positive results can be caused by: 1) absence of lung sliding (e.g., apnea, inflammatory adherences, over-inflation, severe bullous disease, decrease in lung compliance, pleural symphysis, endobronchial intubation); 2) absence of lung pulse in bullous disease and over-inflation/-distension; 3) position of transducer over a rib instead of the intercostal space; and/or 4) misinterpretation of pericardial movement (paracardiac area), diaphragm (supradiaphragmatic area), or transition point between normal lung and lung bullae or adhesions as lung point.