Pneumothorax

need a linear probe 5-10 mHz

Check in two spots, 3 ICS mid clav and below the nipple line on the anterior axillary line

Find the acoustic shadows of the ribs

Find the hypoechoic line between the two ribs, this is the pleural line

Normal lung exhibits comet-tail artifact and lung sliding at this pleural line

The presence of pneumothorax is characterized by two features:

Absence of pleural lung sliding. In normal subjects, the pleural line represents the parietal and visceral layers of the pleura, and is usually characterized by to-and-fro movements, or "sliding" seen during respiratory movements. In cases of pneumothorax, air collection beyond the parietal pleura prevents visualization of the visceral pleura, and, therefore, lung sliding is not observed. This sign is dynamic and has to be observed in real-time scanning. However, the presence or absence of lung sliding can be captured in still image by using M-mode. Figure 2A,2B illustrates the different appearances between a normal anterior chest (Fig. 2a), with lung sliding, and one with pneumothorax (Fig. 2b), without lung sliding, under M-mode.

Absence of comet-tail artifacts Comet-tail artifacts normally arise from the visceral pleura. However, in the case of pneumothorax, air within the pleural space hinders propagation of the sound waves, thereby preventing the formation of such artifacts.
In addition, Lichtenstein et al. also described the "lung point" sign as diagnostic of pneumothorax.7 The lung point is a feature characterized by the fleeting appearance of a normal lung pattern (lung sliding or comet-tail artifacts) replacing a pneumothorax pattern (absent lung-sliding and absent comet-tail artifact) in a particular location of the chest wall.7 As with lung sliding, this dynamic sign is related to the inspiratory and expiratory movements of the respiratory cycle, with the transducer remaining at the same location, and is demonstrable only in real-time examination. It should be searched for by longitudinally scanning the anterior, lateral, and posterior positions of the chest wall.

 

The studies of Lichtenstein et al. involved critically ill patients in an intensive care setting. Absence of lung sliding was found in a prospective operator-blinded study to be a useful sign for pneumothorax, with sensitivity of 95.3%, specificity of 91.1% and negative predictive value of 100%.5 Ultrasound visualization of lung sliding was always correlated with the absence of pneumothorax. It was concluded that pneumothorax may be immediately excluded if the sign of lung sliding was detected. However, the absence of lung sliding also occurred in patients with adult respiratory distress syndrome or acute lung fibrosis, with loss of lung expansion, but without pneumothorax (false-positive cases).

In similar settings, the comet-tail artifact was found to be a useful sign for ruling out pneumothorax.6 The sign of absence of comet-tail artifact had a sensitivity and negative predictive value of 100% and a specificity of 60% for the diagnosis of pneumothorax. Comet-tail artifacts may be absent in normal lungs, but their presence allows exclusion of pneumothorax. The signs of absence of comet-tail artifact and absence of lung sliding, when combined, had a sensitivity and negative predictive value of 100%, and the specificity increased to 96.5%. Furthermore, the lung point sign had an overall sensitivity of 66% and a specificity of 100%.7

While the lung point sign is a relatively new finding warranting further research, the usefulness of the lung sliding and comet-tail artifact signs for the diagnosis of pneumothorax have also been demonstrated and reported by radiologists on patients immediately after ultrasound-guided lung biopsies.2,3,4 One study also attempted to detect the volume of pneumothorax by ultrasound.3

Dulchavsky et al. found that ultrasonography had a sensitivity of 95.5% and a specificity of 100% for the detection of pneumothorax, compared with chest radiography.8 The signs of lung sliding and comet-tail artifact were evaluated by surgical residents and attending physicians before radiologic verification of pneumothorax. It was concluded that ultrasound to detect pneumothorax was reliable, and expansion of the focused abdominal sonography for trauma (FAST) examination to include the thorax was suggested. Ultrasound may possibly be more sensitive than supine anteroposterior (AP) chest radiography in the detection of small pneumothoraces.9 A study in an Italian emergency department setting showed that, in comparison with spiral computed tomography (CT) as the criterion standard, ultrasonography performed in 36 patients with blunt thoracic trauma demonstrated a sensitivity of 94% and specificity of 100% for the diagnosis of pneumothorax.10
(Academic Emergency Medicine 2003 Volume 10, Number 1 91-94)

REFERENCES
Cunningham J, Kirkpatrick AW, Nicolaou S, et al. Enhanced recognition of "lung sliding" with power color Doppler imaging in the diagnosis of pneumothorax. J Trauma. 2002; 52:769–71.[Medline]
Chan SSW. Emergency bedside ultrasound to detect pneumothorax. Acad Emerg Med. 2003; 10:91–4.[Abstract/Free Full Text]
Rowan KR, Kirkpatrick AW, Liu D, et al. Traumatic pneumothorax detection with thoracic US: correlation with chest radiography and CT—initial experience. Radiology. 2002; 225:210–4.[Abstract/Free Full Text]

Crit
Care Med 2005; 33:1231–1238

Intensive Care Med. 1999 Apr;25(4):383-8. Related Articles, Links


The comet-tail artifact: an ultrasound sign ruling out pneumothorax.

Lichtenstein D, Meziere G, Biderman P, Gepner A.

Service de Reanimation Medicale, Hopital Ambroise Pare, Boulogne (Paris), France.

OBJECTIVE: Ultrasound artifacts arising from the lung-wall interface are either vertical (comet-tail artifacts) or horizontal. The significance of these artifacts for the diagnosis of pneumothorax was assessed. DESIGN: Prospective clinical study. SETTING: The medical ICU of a university-affiliated teaching hospital. PATIENTS: We compared 41 complete pneumothoraces with 146 hemithoraces in 73 critically ill patients in which computed tomography showed absence of pneumothorax. MEASUREMENTS: The anterior chest wall was investigated in supine patients using a portable device. The test was defined as positive for complete pneumothorax when only horizontal artifacts were visible, and negative when artifacts arising from the pleural line and spreading up to the edge of the screen (referred to as "comet-tail artifacts") were present. RESULTS: The feasibility was 98%. Ultrasound showed exclusive horizontal artifacts in all 41 analyzable cases of complete pneumothorax. In the pneumothorax-free group, "comet-tail artifacts" were present in 87 cases and exclusive horizontal artifacts in 56. Ultrasound as well as computed tomography showed anterior consolidation or anterior pleural effusion in three cases. Horizontal artifacts had a sensitivity and a negative predictive value of 100% and a specificity of 60% for the diagnosis of pneumothorax. Horizontal artifacts and absent lung sliding, when combined, had a sensitivity and a negative predictive value of 100% and a specificity of 96.5%. CONCLUSIONS: Ultrasound detection of the "comet-tail artifact" at the anterior chest wall allows complete pneumothorax to be discounted.

Crit Care Med. 2005 Jun;33(6):1231-8. Related Articles, Links


Comment in:
Crit Care Med. 2005 Jun;33(6):1425-6.

Ultrasound diagnosis of occult pneumothorax.

Lichtenstein DA, Meziere G, Lascols N, Biderman P, Courret JP, Gepner A, Goldstein I, Tenoudji-Cohen M.

Medical Intensive Care Unit, Hopital Ambroise-Pare, Boulogne (Paris-Ouest), France.

OBJECTIVES: Pneumothorax can be missed by bedside radiography, and computed tomography is the current alternative. We asked whether lung ultrasound could be of any help in this situation. DESIGN: Retrospective study. SETTING: The medical intensive care unit of a university-affiliated teaching hospital. PATIENTS: All patients admitted to the intensive care unit are routinely scanned with whole-body ultrasound (including screening for pneumothorax) and chest radiography. The study population included 200 consecutive undifferentiated intensive care unit patients who received a chest computed tomography scan in addition to ultrasound and chest radiograph. Forty-seven consecutive cases of radioccult pneumothorax were compared with 310 consecutive hemithoraces free from pneumothorax in the intensive care unit. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: Three signs were investigated at the anterolateral chest wall in supine patients: lung sliding, the A line sign, and the lung point. A total of 357 hemithoraces were analyzed in this study, 47 with occult pneumothorax and 310 controls. Four of the 47 cases of pneumothorax were excluded from the final analysis (parietal emphysema) as well as eight of the 310 controls (large dressings), leaving a final study population of 345 hemithoraces in 197 patients. Feasibility was 98%. Ultrasound scans in all 43 examinable patients with pneumothorax showed absent lung sliding, 41 of 43 patients had the A line sign, and 34 exhibited a lung point. Among 302 analyzable controls, 65 had absent lung sliding, 16 of them showed an A line sign, and none showed a lung point. For the diagnosis of occult pneumothorax, the abolition of lung sliding alone had a sensitivity of 100% and a specificity of 78%. Absent lung sliding plus the A line sign had a sensitivity of 95% and a specificity of 94%. The lung point had a sensitivity of 79% and a specificity of 100%. CONCLUSIONS: For the diagnosis of occult pneumothorax, ultrasound can decrease the need for computed tomography.

J Trauma. 2001 Feb;50(2):201-5. Related Articles, Links


Comment in:
J Trauma. 2001 Aug;51(2):423.

Prospective evaluation of thoracic ultrasound in the detection of pneumothorax.

Dulchavsky SA, Schwarz KL, Kirkpatrick AW, Billica RD, Williams DR, Diebel LN, Campbell MR, Sargysan AE, Hamilton DR.

Department of Surgery, Wayne State University School of Medicine, 4201 St. Antoine, Detroit, MI 48201, USA.

BACKGROUND: Thoracic ultrasound may rapidly diagnose pneumothorax when radiographs are unobtainable; the accuracy is not known. METHODS: We prospectively evaluated thoracic ultrasound detection of pneumothorax in patients at high suspicion of pneumothorax. The presence of "lung sliding" or "comet tail" artifacts were determined in patients by ultrasound before radiologic verification of pneumothorax by residents instructed in thoracic ultrasound. Results were compared with standard radiography. RESULTS: There were 382 patients enrolled; the cause of injury was blunt (281 of 382), gunshot wound (22 of 382), stab wound (61 of 382), and spontaneous (18 of 382). Pneumothorax was demonstrated on chest radiograph in 39 patients and confirmed by ultrasound in 37 of 39 patients (95% sensitivity); two pneumothoraces could not be diagnosed because of subcutaneous air; the true-negative rate was 100%. CONCLUSION: Thoracic ultrasound reliably diagnoses pneumothorax. Expansion of the focused abdominal sonography for trauma (FAST) examination to include the thorax should be investigated for terrestrial and space medical applications.

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