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Original Research: CHEST ULTRASONOGRAPHY |

The Dynamic Air Bronchogram: A Lung Ultrasound Sign of Alveolar Consolidation Ruling Out Atelectasis FREE TO VIEW

Daniel Lichtenstein, MD, FCCP; Gilbert Mezière, MD; Julien Seitz, MD
Author and Funding Information

*From the Service de Réanimation Médicale (Drs. Lichtenstein and Seitz), Hôpital Ambroise-Paré, Boulogne (Paris-Ouest), France; and Service de Réanimation Polyvalente (Dr. Mezière), Centre Hospitalier Général, Saint-Cloud (Paris-Ouest), France.

Correspondence to: Daniel A. Lichtenstein, MD, FCCP, Service de Réanimation Médicale, Hôpital Ambroise-Paré, 92100 Boulogne (Paris-Ouest), France; e-mail: dlicht@free.fr


The authors have reported to the ACCP that no significant conflicts of interest exist with any companies/organizations whose products or services may be discussed in this article.

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/site/misc/reprints.xhtml).


© 2009 American College of Chest Physicians


Chest. 2009;135(6):1421-1425. doi:10.1378/chest.08-2281
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Published online

Background:  The objective of this study was to identify the relationship between a dynamic lung artifact, the dynamic air bronchogram, within alveolar consolidation and the diagnosis of pneumonia vs resorptive atelectasis.

Methods:  This prospective study was undertaken within the medical ICU of a university-affiliated teaching hospital. The sample comprised 52 patients with proven pneumonia (pneumonia group) and 16 patients with proven resorptive atelectasis (atelectasis group). All patients had alveolar consolidation with air bronchograms on lung ultrasound, were mechanically ventilated, and received fibroscopy and bacteriological tests. The air bronchogram dynamic was analyzed within the ultrasound area of consolidation.

Results:  The air bronchograms in the pneumonia group yielded the dynamic air bronchogram in 32 patients and a static air bronchogram in 20. In the atelectasis group, air bronchograms yielded a dynamic air bronchogram in 1 out of 16 patients. With regard to pneumonia vs resorptive atelectasis in patients with ultrasound-visible alveolar consolidation with air bronchograms, the dynamic air bronchogram had a specificity of 94% and a positive predictive value of 97%. The sensitivity was 61%, and the negative predictive value 43%.

Conclusions:  In patients with alveolar consolidation displaying air bronchograms on an ultrasound, the dynamic air bronchogram indicated pneumonia, distinguishing it from resorptive atelectasis. Static air bronchograms were seen in most resorptive atelectases and one third of cases of pneumonia. This finding increases the understanding of the pathophysiology of lung diseases within the clinical context and decreases the need for fibroscopy in practice.

Figures in this Article

The accurate causal diagnosis of lung opacities on a bedside chest radiograph in patients who are critically ill is a frequent challenge.1 Two common causes are pneumonia and atelectasis caused by bronchial block to air entry (yielding retractile consolidation), which we will refer to as resorptive atelectasis throughout this text. The usual tests include radiography, CT scan, fibroscopy, and bacteriological tests.

Lung ultrasonography increasingly is being used in patients with critical illness.2 Skill in lung ultrasonography obviates the need for most radiographs and CT scans in helping physicians to diagnose pleural effusion, interstitial syndrome, and pneumothorax.3 The diagnosis of alveolar consolidation has been in practice for many years,4 and the ultrasound signs are now standardized.5 Air bronchograms frequently are visible using ultrasound, and this article investigates the detection of their dynamic behavior. We assume that this dynamic behavior is correlated with satisfactory patency of the airways supplying the consolidated lung and that this sign demonstrates that the consolidation stems from pneumonia and not from resorptive atelectasis. We have shown elsewhere6 for 33 patients with pneumonia (n = 26) or atelectasis (n = 7) a 61% sensitivity and 100% specificity.

Patients

Over a 6-year period, we prospectively studied patients who were critically ill, using the following selection criteria: admitted to a medical ICU, mechanically ventilated, having a suspected (by the managing team, blinded to the ultrasound results) pneumonia or resorptive atelectasis, receiving fibroscopy (ordered at the discretion of the managing team) that showed either an obstacle confirming the resorptive atelectasis (atelectasis group) or a satisfactory airway patency plus positive bacteriological documentation confirming pneumonia (pneumonia group).

Of 84 initial patients (pneumonia group, n = 58; atelectasis group, n = 26), 80 had an ultrasound-visible alveolar consolidation (pneumonia group, n = 56; atelectasis group, n = 24). We included in this study only patients who displayed air bronchograms within the alveolar consolidation (n = 68 patients). Therefore, the pneumonia group included 52 patients, and the atelectasis group included 16 patients. The patients' characteristics are listed in Table 1. All patients were studied consecutively by a part-time ultrasonography operator and do not reflect the frequency of patients with pneumonia or resorptive atelectasis admitted to the medical ICU.

Table Graphic Jump Location
Table 1 Patient Characteristics*

*All patients were admitted to the medical ICU, were mechanically ventilated, and underwent fibroscopy.

†Massive atelectasis on previous lung disease lung in two patients and pneumonia in one.

Procedure

All patients received an ultrasonography examination (EUB-405; Hitachi Medical Corporation; Tokyo, Japan) with a 5-MHz microconvex probe. The ultrasonographers were intensivists trained in critical ultrasonography and were unaware of the final diagnosis. The ultrasonography examination was performed < 1 h before the fibroscopy. Longitudinal scans of the anterior, lateral, and subposterior chest wall (stages 1, 2, and 3) were taken while patients laid in a supine position. The required equipment, ultrasonography technique, clinical landmarks, and normal patterns have been described previously.3,5 The fibroscopy examination (FI-16BS; Pentax; Tokyo, Japan) was made through an endotracheal tube.

Alveolar consolidation (Fig 1) was defined as an image yielding two signs. The first sign is a tissue-like image arising from the pleural line or the lung line plus tissular behavior of this image with no dynamic in the depth-surface axis. The second is the shred sign, which is a shredded deep border of the tissular image, as in a connection with aerated lung.7 Both signs yield 90% sensitivity and 98% specificity for the diagnosis of alveolar consolidation.5

Figure Jump LinkFigure 1 The shred sign. Alveolar consolidation of the lingula. This image shows a mass abutting the pleural line (arrowheads) with a tissue-like pattern. This figure highlights the shredded lower border, limited by the arrows, which is the shred sign. A pleural effusion would have a lower border that is regular and roughly parallel to the pleural line (ie, the lung line).Grahic Jump Location

Air bronchograms were defined as punctiform or linear hyperechoic artifacts within the consolidation. Dynamic air bronchogram was the term used for the centrifugal inspiratory dynamic of air bronchograms (Fig 2, 3). Movement > 1 mm was required. The image had to remain in the probe's plane, meaning that the bronchial axis was in the beam axis. Images of air bronchograms suddenly disappearing from the screen on respiration were not taken into consideration, as this pattern was attributable to an off-plane effect.

Figure Jump LinkFigure 2 Dynamic air bronchogram (real time). Left: tubular bright artifactual structures within a consolidation corresponding to air bronchograms in expiratory time. White arrows indicate consolidated lung tissue. Note punctiform air bronchograms (black arrow). The arrowhead indicates the diaphragm. Right: centrifugal progression of the air bronchograms in inspiratory time (arrows). The excursion can be measured at least equal to 1 cm.Grahic Jump Location
Figure Jump LinkFigure 3 Dynamic air bronchogram (M-mode). The M-mode analyzes one line of the real-time image in function of time, making dynamic events appear on static images. The centrifugal inspiratory shift of the air bronchograms is objectified (somewhat sinusoidal line). Static air bronchograms would yield horizontal lines, indicating absence of dynamic. Exp = expiration; Insp = inspiration.Grahic Jump Location

We assessed the relation between dynamic air bronchograms and the diagnosis of pneumonia vs resorptive atelectasis. The hospital's internal review board approved this study and waived the requirement for informed consent.

In the pneumonia group, ultrasound patterns of alveolar consolidation were located in the right lung in 34 patients, the left lung in 14 patients, and bilaterally in 4 patients. In the atelectasis group, they were located to the right in 4 patients and to the left in 12 patients. In the pneumonia group, a dynamic air bronchogram was observed in 32 patients and a static air bronchogram in 20 patients. In the atelectasis group, a dynamic air bronchogram was observed in 1 patient, and a static air bronchogram in 15 patients.

For the diagnosis of pneumonia vs resorptive atelectasis in patients having ultrasound-visible alveolar consolidation with air bronchograms, the dynamic air bronchogram had a specificity of 94% and a sensitivity of 61%. The positive predictive value was 97% and the negative predictive value 43% (Table 2).

Table Graphic Jump Location
Table 2 Assessment of Dynamic Air Bronchograms

The potential for an ultrasound to distinguish pneumonia from resorptive atelectasis comes first from its ability to document alveolar consolidation. In 98.5% of the patients, acute alveolar consolidations abutted the visceral pleura, creating the mandatory acoustic window for their ultrasound demonstration.5

In this study where all patients were mechanically ventilated, respiratory movement of gas bubbles within the bronchi indicate preserved patency of the airways because the gas bubbles are pushed toward the end of the bronchi by the positive pressure of air. The dynamic air bronchogram also can be seen in patients who are spontaneously breathing, assuming that the bubbles are attracted by the negative pleural pressure. The M-mode objectifies this shift, yielding a somewhat sinusoidal line, which is always centrifugal on inspiration. Lung sliding indicates absence of resorptive atelectasis.8 Similarly, the dynamic air bronchogram is a sign indicating the absence of resorptive atelectasis.

Resorptive atelectasis yields early and late signs. One early sign is abolished lung sliding associated with the lung pulse, a cardiac activity visible through abolished lung sliding.8 Another early sign is a standstill cupola, a sign of interest that demonstrates the absence of lung expansion. The late signs appear when the gas is progressively absorbed, yielding a radiologic image of consolidation with loss of volume, which includes the static air bronchogram. Note that residual bronchial gas can be seen within atelectasis; this pattern, rarely seen on radiograph, is common on CT scans. The detection of air bronchograms is probably more accurate on an ultrasound than on a radiograph. Studies have proven ultrasonography's superiority to radiography9 or even CT scan10 for detecting pleural effusion, alveolar consolidation, necrotizing pneumonia, interstitial syndrome, and pneumothorax. The dynamic air bronchogram also is found in ventilated newborns who are critically ill. In these fragile patients, this application can provide a solution for decreasing medical irradiation.11,12

Clinical Relevance of the Dynamic Air Bronchogram

In our study series, traditional tools (ie, clinical judgment, clinical examination, chest radiography) did not yield an obvious diagnosis of atelectasis in 6 of the 24 patients. Ultrasound is useful every time the origin of a consolidation is unclear (ill-defined radiograph) or if radiography is not done, as in the case of fragile patients (ie, children, pregnant women) or any area where resources are scarce. An ultrasound shows not only the consolidation, as would radiograph or CT scan, but also a dynamic sign of clinical relevance. Because this sign is associated to a nonretractile consolidation (ie, not an atelectasis), it indicates that this consolidation is probably a pneumonia and that there is no immediate need for fibroscopy to search for an obstacle. Real-time lung expansion is one major advantage of ultrasonography compared to traditional imaging approaches such as radiography or CT scan, which cannot demonstrate lung expansion in real time. Possibly of interest is fluoroscopy, which currently is not performed in patients who are critically ill.

Pathophysiologic Notes

For simplicity, we have used the term atelectasis to designate a radiologic image because it is commonly used for describing areas of attenuation seen in radiographs or CT scans. Stricto sensu, atelectasis means absence of peripheral lung expansion, implying a functional, not anatomic, disorder. One-lung intubation is a quasiexperimental model of complete resorptive atelectasis. The early signs on an ultrasound are immediately visible. Any person can reproduce a complete bilateral atelectasis, so to speak, simply by halting breathing. This highly unstable situation immediately provides abolition of lung sliding, standstill cupola, lung pulse, and oxygen desaturation. Obviously, the person will breathe again long before generation of a bilateral alveolar consolidation, which should be the next logical pathophysiologic step. In a patient with conventional mechanical ventilation, abolished lung sliding with lung pulse, a frequent finding, is definitely pathological.

We assume that the sound generated by the dynamic air bronchogram is the rale, most of the time associated. Compressed by the upstream airway pressure, the small gas bubbles should generate this characteristic crepitation. The rale has been proven9 to have high specificity (and low sensitivity) for alveolar consolidation.

Limitations

This study considered only patients within a medical ICU having an ultrasound-visible alveolar consolidation containing air bronchograms. The rates do not refer to a population of patients having only alveolar consolidations.

The probe beam must be located at the exact bronchial axis, and the operator's hand must scan the volume of the consolidation to increase the ultrasound's sensitivity. Interobserver agreement has to be measured for this application, although the authors find this sign easy to assess. The search for an air bronchogram in small alveolar volumes, however, may be difficult. An atelectasis can complicate a pneumonia and would generate a nonspecific consolidation without air bronchogram or with static air bronchogram, a frequent finding in pneumoniae.

We did not deal with other causes of alveolar consolidation seen in patients who are critically ill, including lung infarction, pulmonary edema, and tumors. Additionally, the training in lung ultrasound classically is considered a limitation (see discussion in the next section).

Various Considerations

The unsophisticated machine we use (EUB-405; Hitachi Medical Corp) provides an optimal resolution quality (see Figs 13), is 29 cm wide (33 cm with the cart), provides a major advantage for hospital use as it has a flat keyboard that allows for rapid disinfection, and starts up in 7 seconds. Our 5-MHz microconvex probe covering 1 to 17 cm allows a whole-body approach to patients who are critically ill.13 The absence of Doppler reduces the machine's cost. Note that the dynamic air bronchogram was described using a 1982-era device (ADR-4000; Advanced Technology Laboratories; Tempe, AZ) [see online video clip].

Using a suitable unit and standardized training in authorized centers delivering a step-by-step program, lung ultrasonography training provides a 0.89 concordance test acquired after limited training for diagnosing alveolar consolidation.5 The dynamic air bronchogram is a self-speaking sign (see online video clip). Lung ultrasonography's utility has been confirmed by a growing number of studies1425 and is simple to perform, provided one thinks differently.26

In patients with ultrasound-visible alveolar consolidation displaying air bronchograms, the dynamic air bronchogram had a 94% specificity and a 97% positive predictive value for diagnosing pneumonia and distinguishing it from resorptive atelectasis. Static air bronchograms were seen in most resorptive atelectases and in one third of patients with pneumonia. Associated with the clinical data, this finding allows for a better understanding of the pathophysiology of lung diseases and, in some instances, leads to decreasing the need for fibroscopy.

The authors thank François Jardin for his trust.

Wiener MD, Garay SM, Leitman BS, et al. Imaging of the ICU patient. Clin Chest Med. 1991;12:169-198. [PubMed]
 
Weinberger SE, Drazen JM. Diagnostic procedures in respiratory diseases. Harrison's principles of internal medicine. 2005;16th ed. New York, NY McGraw-Hill:1505-1508
 
Lichtenstein D. Ultrasound in the management of thoracic disease. Crit Care Med. 2007;35suppl:S250-S261. [PubMed] [CrossRef]
 
Weinberg B, Diakoumakis EE, Kass EG, et al. The air bronchogram: sonographic demonstration. AJR Am J Rontgenol. 1986;147:593-595
 
Lichtenstein D, Lascols N, Mezière G, et al. Ultrasound diagnosis of alveolar consolidation in the critically ill. Intensive Care Med. 2004;30:276-281. [PubMed]
 
Lichtenstein D, Mezière G, Seitz J. The dynamic air bronchogram: an ultrasound sign of nonretractile alveolar consolidation. Reanimation. 2002;11suppl:98s
 
Lichtenstein D, Mezière G. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE-protocol. Chest. 2008;134:117-125. [PubMed]
 
Lichtenstein D, Lascols N, Prin S, et al. The lung pulse: an early ultrasound sign of complete atelectasis. Intensive Care Med. 2003;29:2187-2192. [PubMed]
 
Lichtenstein D, Goldstein I, Mourgeon E, et al. Comparative diagnostic performances of auscultation, chest radiography and lung ultrasonography in acute respiratory distress syndrome. Anesthesiology. 2004;100:9-15. [PubMed]
 
Lichtenstein D, Peyrouset O. Lung ultrasound superior to CT? The example of a CT-occult necrotizing pneumonia. Intensive Care Med. 2006;32:334-335. [PubMed]
 
Brenner DJ, Hall EJ. Computed tomography: an increasing source of radiation exposure. N Engl J Med. 2007;357:2277-2284. [PubMed]
 
Berrington de Gonzales A, Darby S. Risk of cancer from diagnostic x-rays. Lancet. 2004;363:345-351. [PubMed]
 
Lichtenstein D. General ultrasound in the critically ill. 2005; Berlin, Germany Springer
 
Bitschnau R, Mathis G. Chest ultrasound in the diagnosis of acute pulmonary embolism. Radiology. 1999;211:290. [PubMed]
 
Maury E, Guglielminotti J, Alzieu M, et al. Ultrasonic examination: an alternative to chest radiography after central venous catheter insertion? Am J Respir Crit Care Med. 2001;164:403-405. [PubMed]
 
Rowan KR, Kirkpatrick AW, Liu D, et al. Traumatic pneumothorax: detection with thoracic US: correlation with chest radiography and CT. Radiology. 2002;225:210-214. [PubMed]
 
Mayo PH, Goltz HR, Tafreshi M, et al. Safety of ultrasound-guided thoracentesis in patients receiving mechanical ventilation. Chest. 2004;125:1059-1062. [PubMed]
 
Jambrik Z, Monti S, Coppola V, et al. Usefulness of ultrasound lung comets as a nonradiologic sign of extravascular lung water. Am J Cardiol. 2004;93:1265-1270. [PubMed]
 
Chun R, Kirkpatrick AW, Sirois M, et al. Where's the tube? Evaluation of hand-held US in confirming ET tube placement. Prehosp Disaster Med. 2004;19:366-369. [PubMed]
 
Blaivas M, Lyon M, Duggal S. A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax. Acad Emerg Med. 2005;12:844-849. [PubMed]
 
Volpicelli G, Mussa A, Garofalo G, et al. Bedside lung ultrasound in the assessment of alveolar-interstitial syndrome. Am J Emerg Med. 2006;24:689-696. [PubMed]
 
Soldati G, Testa A, Silva FR, et al. Chest ultrasonography in lung contusion. Chest. 2006;130:533-538. [PubMed]
 
Copetti R, Catarossi L. The double lung point, an ultrasound sign diagnostic of transient tachypnea of the newborn. Neonatalogy. 2007;91:203-209
 
Fagenholz PJ, Gutman JA, Murray AF, et al. Chest ultrasonography for the diagnosis and monitoring of high-altitude pulmonary edema. Chest. 2007;131:1013-1018. [PubMed]
 
Bouhemad B, Zhang M, Lu Q, et al. Clinical review: bedside lung ultrasound in critical care practice. Crit Care. 2007;11:205. [PubMed]
 
van der Werf TS, Zijlstra JG. Ultrasound of the lung: just imagine. Intensive Care Med. 2004;30:183-184. [PubMed]
 

Figures

Figure Jump LinkFigure 1 The shred sign. Alveolar consolidation of the lingula. This image shows a mass abutting the pleural line (arrowheads) with a tissue-like pattern. This figure highlights the shredded lower border, limited by the arrows, which is the shred sign. A pleural effusion would have a lower border that is regular and roughly parallel to the pleural line (ie, the lung line).Grahic Jump Location
Figure Jump LinkFigure 2 Dynamic air bronchogram (real time). Left: tubular bright artifactual structures within a consolidation corresponding to air bronchograms in expiratory time. White arrows indicate consolidated lung tissue. Note punctiform air bronchograms (black arrow). The arrowhead indicates the diaphragm. Right: centrifugal progression of the air bronchograms in inspiratory time (arrows). The excursion can be measured at least equal to 1 cm.Grahic Jump Location
Figure Jump LinkFigure 3 Dynamic air bronchogram (M-mode). The M-mode analyzes one line of the real-time image in function of time, making dynamic events appear on static images. The centrifugal inspiratory shift of the air bronchograms is objectified (somewhat sinusoidal line). Static air bronchograms would yield horizontal lines, indicating absence of dynamic. Exp = expiration; Insp = inspiration.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1 Patient Characteristics*

*All patients were admitted to the medical ICU, were mechanically ventilated, and underwent fibroscopy.

†Massive atelectasis on previous lung disease lung in two patients and pneumonia in one.

Table Graphic Jump Location
Table 2 Assessment of Dynamic Air Bronchograms

References

Wiener MD, Garay SM, Leitman BS, et al. Imaging of the ICU patient. Clin Chest Med. 1991;12:169-198. [PubMed]
 
Weinberger SE, Drazen JM. Diagnostic procedures in respiratory diseases. Harrison's principles of internal medicine. 2005;16th ed. New York, NY McGraw-Hill:1505-1508
 
Lichtenstein D. Ultrasound in the management of thoracic disease. Crit Care Med. 2007;35suppl:S250-S261. [PubMed] [CrossRef]
 
Weinberg B, Diakoumakis EE, Kass EG, et al. The air bronchogram: sonographic demonstration. AJR Am J Rontgenol. 1986;147:593-595
 
Lichtenstein D, Lascols N, Mezière G, et al. Ultrasound diagnosis of alveolar consolidation in the critically ill. Intensive Care Med. 2004;30:276-281. [PubMed]
 
Lichtenstein D, Mezière G, Seitz J. The dynamic air bronchogram: an ultrasound sign of nonretractile alveolar consolidation. Reanimation. 2002;11suppl:98s
 
Lichtenstein D, Mezière G. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE-protocol. Chest. 2008;134:117-125. [PubMed]
 
Lichtenstein D, Lascols N, Prin S, et al. The lung pulse: an early ultrasound sign of complete atelectasis. Intensive Care Med. 2003;29:2187-2192. [PubMed]
 
Lichtenstein D, Goldstein I, Mourgeon E, et al. Comparative diagnostic performances of auscultation, chest radiography and lung ultrasonography in acute respiratory distress syndrome. Anesthesiology. 2004;100:9-15. [PubMed]
 
Lichtenstein D, Peyrouset O. Lung ultrasound superior to CT? The example of a CT-occult necrotizing pneumonia. Intensive Care Med. 2006;32:334-335. [PubMed]
 
Brenner DJ, Hall EJ. Computed tomography: an increasing source of radiation exposure. N Engl J Med. 2007;357:2277-2284. [PubMed]
 
Berrington de Gonzales A, Darby S. Risk of cancer from diagnostic x-rays. Lancet. 2004;363:345-351. [PubMed]
 
Lichtenstein D. General ultrasound in the critically ill. 2005; Berlin, Germany Springer
 
Bitschnau R, Mathis G. Chest ultrasound in the diagnosis of acute pulmonary embolism. Radiology. 1999;211:290. [PubMed]
 
Maury E, Guglielminotti J, Alzieu M, et al. Ultrasonic examination: an alternative to chest radiography after central venous catheter insertion? Am J Respir Crit Care Med. 2001;164:403-405. [PubMed]
 
Rowan KR, Kirkpatrick AW, Liu D, et al. Traumatic pneumothorax: detection with thoracic US: correlation with chest radiography and CT. Radiology. 2002;225:210-214. [PubMed]
 
Mayo PH, Goltz HR, Tafreshi M, et al. Safety of ultrasound-guided thoracentesis in patients receiving mechanical ventilation. Chest. 2004;125:1059-1062. [PubMed]
 
Jambrik Z, Monti S, Coppola V, et al. Usefulness of ultrasound lung comets as a nonradiologic sign of extravascular lung water. Am J Cardiol. 2004;93:1265-1270. [PubMed]
 
Chun R, Kirkpatrick AW, Sirois M, et al. Where's the tube? Evaluation of hand-held US in confirming ET tube placement. Prehosp Disaster Med. 2004;19:366-369. [PubMed]
 
Blaivas M, Lyon M, Duggal S. A prospective comparison of supine chest radiography and bedside ultrasound for the diagnosis of traumatic pneumothorax. Acad Emerg Med. 2005;12:844-849. [PubMed]
 
Volpicelli G, Mussa A, Garofalo G, et al. Bedside lung ultrasound in the assessment of alveolar-interstitial syndrome. Am J Emerg Med. 2006;24:689-696. [PubMed]
 
Soldati G, Testa A, Silva FR, et al. Chest ultrasonography in lung contusion. Chest. 2006;130:533-538. [PubMed]
 
Copetti R, Catarossi L. The double lung point, an ultrasound sign diagnostic of transient tachypnea of the newborn. Neonatalogy. 2007;91:203-209
 
Fagenholz PJ, Gutman JA, Murray AF, et al. Chest ultrasonography for the diagnosis and monitoring of high-altitude pulmonary edema. Chest. 2007;131:1013-1018. [PubMed]
 
Bouhemad B, Zhang M, Lu Q, et al. Clinical review: bedside lung ultrasound in critical care practice. Crit Care. 2007;11:205. [PubMed]
 
van der Werf TS, Zijlstra JG. Ultrasound of the lung: just imagine. Intensive Care Med. 2004;30:183-184. [PubMed]
 
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