Lung Ultrasound in Pneumothorax: The Continuing ...

The Journal of Emergency Medicine, Vol. -, No. -, pp. 1–2, 2017 Ó 2017 Elsevier Inc. All rights reserved. 0736-4679/$ - see front matter

Letter to the Editor , LUNG ULTRASOUND IN PNEUMOTHORAX: THE CONTINUING NEED FOR APPROPRIATE USE AND CORRECT INTERPRETATION

technique used and the patients’ conditions, the readers would be unable to make conclusions about the scientific validity of the data obtained in the study. Moreover, the study of Press et al. was specifically designed for testing the ability of paramedic novices in the first ultrasound diagnosis of trauma emergencies during helicopter transportation to decide on emergency interventions, not to evaluate lung ultrasound for pneumothorax; this invalidates any serious consideration of the test performance (2). In their study, Press et al. obtained a low sensitivity of lung ultrasound for pneumothorax, whereas specificity was high (2). Their data are surprising, but a careful reader with some experience in lung ultrasound should consider the limitations of the study prior to drawing conclusions. In the study protocol, pneumothorax was confirmed based only on the absence of sliding, which is notoriously a sign that is not sufficiently specific when considered alone. Thus, if the authors did not consider a combination of absence of sliding with absence of lung pulse and B lines (and consolidations) or the visualization of a lung point, the specificity obtained is surprisingly high. Conversely, sensitivity was surprisingly low. This is in contrast to the existing literature, as many other studies have shown that lung ultrasound has a sensitivity strikingly superior to chest radiography (4). However, the same authors are not fully convinced by their own data, as they comment that the “use of a large pool of novice sonographers” and “the difficult conditions” due to “helicopter vibrations” might have influenced the large number of false negative scans. False negative means that the operator detects lung sliding in a condition of pneumothorax. How is it possible? As physics is not an opinion, sliding cannot be detected when the ultrasound probe is leaning on an area of the chest wall where intrapleural air interposes to the lung. There are two possible explanations for the controversy. The first is that strong helicopter vibrations and study participant inexperience may have influenced the visualization of false sliding. It is intuitive that performing lung ultrasound in problematic conditions, such as during helicopter transportation, needs higher skill and more experience than in the evaluation of a bedridden patient in the emergency department (ED). Indeed, a similar challenge is encountered when

, To the Editor: I read with interest the letter sent by Trovato and Sperandeo, who comment on the study published by Press et al. (1,2). I found there are some considerations that reveal the weakness of the arguments reported in the letter and that show a great limitation of the study. In their letter, Trovato and Sperandeo report personal data to support the idea that accuracy of lung ultrasound for pneumothorax is insufficient (1). It is my opinion that their personal data are not detailed enough to support this idea. I can only observe that using chest radiography as the gold standard intuitively represents a great limitation. Moreover, Trovato and Sperandeo make a methodological error, when they report in the letter, “We searched for partial or nontotal TUS signs of pneumothorax (no pleural gliding, no lung point.)” (1). However, absence of lung point cannot be considered a sign of pneumothorax. The authors forget that the lung point is the only sign useful to confirm and not to rule out pneumothorax (3). The authors report a huge number of cases and I wonder why they do not publish their study as an original contribution in a high-ranking journal, reporting in detail the methodology used. That would be the only way to seriously consider their data. Without such validation, data reported in letters remain conversational and cannot contribute to scientific progress. I also appreciated reading the study of Press et al., but surprisingly, I did not find enough details on the methodology used for lung ultrasound (2). How did the operators perform lung ultrasound for pneumothorax? Which probe and machine did they use? How and where was the probe positioned? We know that lung ultrasound for pneumothorax is based on the detection of four basic signs: sliding, B-lines, pulse, and lung point. Which combination of ultrasound signs was investigated? Even more importantly, the diagnostic accuracy of the ultrasound signs for pneumothorax depends on the hemodynamic condition of the patient. Without knowing in detail the 1

2

low-quality chest x-ray films, obtained at the bedside in the ED, need great expertise for a correct reading. Second, sensitivity of lung ultrasound for pneumothorax is strictly dependent on the chest area where the probe is placed. Detection of sliding rules out with certainty pneumothorax, but only in the area where the sign is visualized. In the vast majority of pneumothorax cases, when the patient lies down in the supine position, pleural air moves superiorly. Thus, visualization of lung sliding in the anterior chest in the supine patient is enough to rule out the condition with high sensitivity (3). However, there are complex conditions in which scanning the thorax in only one area is not enough (5). For instance, blunt trauma or recurrence in previous pleurodesis often presents complex situations that need a more careful evaluation. In these cases, pleural adhesions originated by contusions or septa may cause loculated or septated pneumothorax (6). In severe blunt thoracic trauma, when the first examination of the anterior chest is negative but still the suspicion of loculated pneumothorax is strong, a whole chest examination is mandatory. Was it performed in the study? In conclusion, the study of Press et al. has too many technical limitations to draw conclusions beyond its purely original scope, which was testing the ability of paramedic novices in the first ultrasound diagnosis of

Letters to the Editor

trauma emergencies during helicopter transportation (2). Any comment on ultrasound accuracy for the diagnosis of pneumothorax that is based on this study or on personal unpublished data cannot be considered a valid support to scientific progress. Giovanni Volpicelli, MD Emergency Medicine San Luigi Gonzaga University Hospital Torino, Italy http://dx.doi.org/10.1016/j.jemermed.2017.03.048 REFERENCES 1. Trovato G, Sperandeo M. Lung ultrasound in pneumothorax: the continuing need for radiology. J Emerg Med 2016;51:189–91. 2. Press GM, Miller SK, Hassan IA, et al. Prospective evaluation of prehospital trauma ultrasound during aeromedical transport. J Emerg Med 2014;47:638–45. 3. Volpicelli G. Sonographic diagnosis of pneumothorax. Intensive Care Med 2011;37:224–32. 4. Ding W, Shen Y, Yang J, He X, Zhang M. Diagnosis of pneumothorax by radiography and ultrasonography: a meta-analysis. Chest 2011; 140:859–66. 5. Volpicelli G, Boero E, Stefanone V, et al. Unusual new signs of pneumothorax at lung ultrasound. Crit Ultrasound J 2013;5:10. 6. Volpicelli G, Garofalo G, Lamorte A, et al. Images in emergency medicine. Young man with left thoracic pain. Recurrent pneumothorax after failed pleurodesis. Ann Emerg Med 2012;60:e3–4.