Thoracic Ultrasound

Indications

  • Evaluation of Pleural Effusion: effusion characteristics can be evaluated (such as amount of pleural fluid, degree of loculation, etc)
  • Evaluation for Pneumothorax (see Pneumothorax, [[Pneumothorax]])

Technique

  • Place Transducer in Interspace Between the Ribs: assess systematically in 4 anterior chest wall quadrants

Normal Lung Anatomy by Ultrasound

2D Ultrasound

Pleural Line

  • Definition: bright, shimmering line observed approximately 0.5 cm deep to the rib cortex

Lung Sliding

  • Definition: sliding appearance at interface between visceral and parietal pleura, indicating that the lung is inflated and moving (during tidal ventilation)
  • Technique
    • In a Mechanically Ventilated Patient, Increase the Tidal Volume to Accentuate Visualization of Lung Sliding
    • Decrease the Gain and Depth to Accentuate Visualization of Lung Sliding
    • Lung Sliding May Be Less Apparent at the Apices: however, even the slightest movement is significant (“All or Nothing” Rule)
  • Etiology-Lung Sliding Present
    • Normal
  • Etiology-Lung Sliding Absent
    • Pneumothorax (see Pneumothorax, [[Pneumothorax]]): absence of lung sliding alone has 100% sensitivity/78% specificity for pneumothorax [MEDLINE]
    • Diaphragmatic Paralysis
    • Endobronchial Obstruction
    • Post-Pleurodesis/Pleural Adhesions

Lung Pulse

  • Definition: phasic sliding of interface between visceral and parietal pleura associated due to cardiac motion

A-Lines

  • Definition: equally-spaced parallel horizontal lines within the lung (seen at a multiple of distance from the pleural line to the skin, parellel to the pleural line)
    • A-Lines Represent a Reverberation Artifact: they are observed in normal lung, diseased lung, and pneumothorax
    • Presence of A-Lines Over the Entire Chest (Unilateral or Bilateral) Rules Out Cardiogenic Pulmonary Edema: presence of such an A-line pattern indicates that the PCWP <18 mm Hg [MEDLINE]

B-Lines

  • Definition: perpendicular, vertical lines extending from the pleural line to bottom of the ultrasound screen
  • B-Lines are Generated by the Visceral and Not the Parietal Pleura: therefore, presence of B-lines indicates that the lung inflated and they are not visible in pneumothorax [MEDLINE]
  • Mandatory Features of B-Lines [MEDLINE]
    • Arise From the Pleural Line
    • Erase the A-Lines
    • Move with Lung Sliding: presence of B-lines indicates that the lung is inflated
    • Extend to the Bottom Edge of the Ultrasound Screen without Fading (“Lung Rockets”, “Comet Tails”)
    • Well-Defined (Laser Beam-Like)
  • Number of B-Lines
    • More Than 3 B-Lines Per Field is Abnormal: normal patients can have a few B-lines over the lower lateral chest and occasionally single B-lines in other locations
  • Spacing of B-Lines
    • B-Lines 7 mm Apart (B7 Lines) Represent Thickened Interlobular Septae (Equivalent to Kerley B Lines) [MEDLINE]
    • B-Lines 3 mm Apart (B3 Lines) Represent Ground Glass Infiltrates [MEDLINE]

B-LINES

Z-Lines

  • Mandatory Features of Z-Lines
    • Arise from the Pleural Line
    • Do Not Erase the A-Lines
    • Ill-Defined
    • Independent of Lung Sliding
    • Vanish After a Few Centimeters (2-5 cm)
  • Clinical Correlate: Z-Lines have no pathologic significance
    • Found in both normal patients and in pneumothorax

O Line Pattern

  • Definition: absence of both A-lines and B-lines

M-Mode Ultrasound

  • “Seashore Sign”: the presence of seashore sign rules out the presence of a pneumothorax
    • Wavelike Pattern Above the Pleural Line: pleural line is indicated by the red arrow
    • Sandlike Pattern Below the Pleural Line (Produced by Movement of the Lung Below the Pleural Line): pleural line is indicated by the red arrow

SEASHORE


Evaluation for Alveolar/Interstitial Lung Abnormalities

2D Ultrasound Features

  • A-Lines
    • Presence of A-Lines Over the Entire Chest (Unilateral or Bilateral) Rules Out Cardiogenic Pulmonary Edema: presence of such an A-line pattern indicates that the PCWP <18 mm Hg [MEDLINE]
  • B-Lines
    • B-Lines Probably Represent Thickened Interlobular Septae
    • Diffuse B-Line Pattern with Smooth Pleural Line: indicates the presence of cardiogenic pulmonary edema
    • Diffuse B-Line Pattern with Rough Pleural Line: indicates the presence of ARDS, ILD, or pneumonia
      • B-line distribution is heterogeneous with small subpleural areas of lung consolidation
  • Consolidated Lung: appears similar in density to liver and spleen
  • Air Bronchograms: may be seen as punctate echogenic foci within the consolidated lung
    • If they move in synchrony with the respiratory cycle, the bronchus supplying the area is patent
  • E-Lines (E = Emphysema)
    • E-Lines Arise from Superficial Collections of Parietal/Subcutaneous Emphysema
    • Features of E-Lines
      • Arise From Above the Pleural Line
      • Pleural Line is Not Visible
      • Spreads to the Bottom Edge of the Ultrasound Screen without Fading

Evaluation for Pneumothorax

US DX OF PTX

General Evaluation

  • Location of Assessment: several areas of chest should be assessed when pneumothorax is suspected, especially areas where air would likely accumulate (anterior-superior and lateral chest wall)

2D Ultrasound Features Which Indicate Pneumothorax

  • Absence of Lung Sliding/Lung Pulse
    • Presence of Lung Sliding/Lung Pulse: rules out the presence of pneumothorax
      • Presence of Lung Sliding and B-Lines Has a 100% Negative Predictive Value for Ruling Out Pneumothorax (in the Area of the Probe) [MEDLINE] [MEDLINE]
  • Presence of Lung Point: intermittent visualization of lung sliding from mobile partially collapsed lung -> sliding part of lung comes on/off of the screen
    • Sensitivity: the sensitivity of lung point for pneumothorax is inversely proportional to the size of the pneumothorax: since a large pneumothorax would prevent lung parenchyma from opposing the chest wall
    • Specificity: lung point has a 100% specificity for pneumothorax -> lung point is diagnostic of pneumothorax [MEDLINE]
  • Presence of A-Lines: since A-lines are observed in normal lung, diseased lung, and pneumothorax
  • Absence of B-Lines
    • B-Lines are Generated by the Visceral and Not the Parietal Pleura: therefore, presence of B-lines indicates that the lung inflated and they are not visible in pneumothorax [MEDLINE]
    • Presence of Lung Sliding and B-Lines Has a 100% Negative Predictive Value for Ruling Out Pneumothorax (in the Area of the Probe) [MEDLINE] [MEDLINE]

M-Mode Ultrasound Features Which Indicate Pneumothorax

  • Presence of “Stratosphere Sign”: strictly horizontal lines replace the normal granular (sandy) pattern of the lung, indicating the presence of gas below the pleural line
    • Specificity: the stratosphere sign is not specific to pneumothorax
    • Presence of “Seashore Sign”: rules out pneumothorax
  • Presence of Lung Point: abrupt transition from seashore sign to stratosphere sign

References

  • Radiology in heart disease. Br Med J 1933; 2:594 [MEDLINE]
  • A bedside ultrasound sign ruling out pneumothorax in the critically ill. Lung sliding. Chest 1995;108(5):1345-1348 [MEDLINE]
  • The comet-tail artifact: An ultrasound sign of alveolar-interstitial syndrome. Am J Respir Crit Care Med 1997; 156:1640-1646 [MEDLINE]
  • The comet-tail artifact, an ultrasound sign ruling out pneumothorax. Intensive Care Med 1999; 25:383–388 [MEDLINE]
  • The “lung point”: an ultrasound sign specific to pneumothorax. Intensive Care Med  2000; 26:1434-1440 [MEDLINE]
  • Ultrasonic examination: an alternative to chest radiography after central venous catheter insertion? Am J Respir Crit Care Med. 2001;164(3):403-405 [MEDLINE]
  • Ultrasound diagnosis of occult pneumothorax. Crit Care Med 2005; 33(6):1231-1238 [MEDLINE]
  • Ultrasound comet-tail images: a marker of pulmonary edema: a comparative study with wedge pressure and extravascular lung water. Chest 2005;127(5):1690-1695 [MEDLINE]
  • Pleural ultrasonography.  Clin Chest Med 2006; 27:215-227 [MEDLINE]
  • Clinical review: bedside lung ultrasound in critical care practice.  Crit Care 2007; 11:205 [MEDLINE]
  • Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest 2008;134(1):117-125 [MEDLINE]
  • 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 [MEDLINE]
  • Pleural procedures and thoracic ultrasound: British Thoracic Society Pleural Disease Guideline.  Thorax 2010; 65(Suppl 2):ii61-ii76 [MEDLINE]
  • Thoracic Ultrasonography for the Pulmonary Specialist. Chest 2011; 140(5):1332–1341 [MEDLINE]
  • Sonographic diagnosis of pneumothorax. Intensive Care Med 2011; 37:224-232 [MEDLINE]
  • Clinical applications of bedside ultrasonography in internal and emergency medicine. Intern Emerg Med 2011 Jun;6(3):195-201. doi: 10.1007/s11739-010-0424-3. Epub 2010 Aug 3 [MEDLINE]
  • Can chest ultrasonography substitute standard chest radiography for evaluation of acute dyspnea in the emergency department? Chest 2011; 139(5):1140-1147 [MEDLINE]
  • Lung ultrasound in the ICU: From diagnostic instrument to respiratory monitoring tool.  Minerva Anestesiol  2012; 78:1282-1296 [MEDLINE]
  • Pneumothorax in the critically ill patient.  Chest 2012; 141:1098-1105 [MEDLINE]
  • Lung ultrasound in the critically ill. Ann Intensive Care. 2014;4:1 [MEDLINE]