Lung Ultrasound Workshop Objectives: Introduction Ultrasound transducers and physics

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1 Lung Ultrasound Massimiliano Meineri MD Assistant Professor of Anesthesiology Department of Anesthesiology Toronto General Hospital University of Toronto Katherine Grichnik MD Professor of Anesthesiology Division of Cardiothoracic Anesthesiology and Critical Care Medicine Duke University Medical Center Workshop Objectives: List the indications for lung ultrasound in the ICU, ER and Post Anesthesia Care Unit. Describe the technique used to perform lung ultrasound. Compare and contrast lung ultrasound to other imaging modalities. Apply ultrasound technology for the study of the lung. Review standard echocardiographic views of the lungs and the anatomical correlates. Discuss common pathological findings. Introduction Ultrasound (US) has been excluded from assessment of lung pathology for many decades. In fact, the acoustic characteristics of thoracic structures make them unsuitable for morphological US imaging in most cases. Bone and air are notorious enemies of US as they prevent their penetration thus obscuring deeper structures. Lung ultrasound relies on interpretation of many different artifacts and patterns. In the hands of trained sonographer, lung US showed a 90% accuracy in diagnosing the cause of respiratory failure in the Emergency Department and can have a higher sensitivity and specificity than chest X ray or physical examination for the detection of pleural effusions and pneumothorax. Its obvious advantages include: decreasing patients exposure to radiation and providing critical diagnostic information quickly at the bedside. For these reasons for the use of bedside lung ultrasound continues to gain popularity among critical care and emergency physicians. The American College of Chest Physicians has defined the knowledge and technical elements required for Competence in Lung US in a recent consensus conference. There is a lack of an established training pathway for certification in North America. Further, training and performance of lung US varies widely among institutions. Ultrasound transducers and physics Various transducers can be used to perform lung US. Linear, phased array (cardiac) or micro convex transducers are most commonly used (Fig.1). A high frequency linear probes creates excellent image definition, but at the cost of lower tissue penetration (max approx 10 cm). The phased array and the micro convex transducers have the advantage of a very small footprint that allows positioning of the US between the ribs, minimizing shadow. The acoustic impedance of various tissues of the thorax determines the US penetration and reflection, which determine the brighter or darker signals (Tab.1). Adjacent tissues with 1

2 significantly different acoustic impedances may be strong reflectors (alveolar tissue and air) and thus result in artifacts. Interpretation of artifacts and their typical signs (tab.2) is the essence of lung US. Fig.1 Ultrasound transducers and Scanning Sectors Tab 1 Echogenicity Hypoechoic (Bright) Isoechoic Hypoechoic (Dark) Air Diaphragm Periostium Liver Kidney Muscles Spleen Fluid Blood Fat Tab 2 Signs Main name Appearance Clinical correlation Bat Sign Using a large footprint transducer: Rib lines are bat wings and the Normal Lung Pleural line is the bat s back. Sea shore Sign Granular appearance of grainy far field with sudden transition to r Normal Lung parallel lines in the near field. Curtain Sign White shadow by air filled lung during inspiration that obscures intra Normal Lung pleural structures. Stratosphere Sign M mode Series of parallel lines from near field to far field. Pneumothorax Lung Point Clear vertical transition from Stratosphere sign to seashore sign. Pneumothorax Quad Sign Quadrangular hypoechoic space between the chest wall and the atelectatic lung. Pleural Effusion Sinusoid Sign M mode Sinusoid appearance of lung line during ventilation. Pleural Effusion Shredded pattern Hyperechoic structure with bright irregular surface. Consolidation 2

3 Scanning Technique To perform lung US, the patient is positioned in a semi-recumbent position with the back elevated approximately 30 with the arms externally rotated and abducted. After application of ultrasound gel the probe in positioned on the chest wall perpendicular to the skin with the index marker (dot or grove) always pointing at the patient s head (Fig 1). The image marker on the screen corresponds to the index marker on the probe and is positioned to the right of the screen, if using cardiology convention and on the left, if using radiology convention. We will be using the cardiology convention from here on. Gain and depth are adjusted to obtain clear distinction of shades of grey and to cover the whole lung depth. Anterior and posterior axillary lines divide the chest wall into three fields: Anterior, Lateral and Posterior. The fields are further divided into equal quadrants for a total of on seven on each side. The lung is scanned longitudinally moving from cranio-caudally to cover all quadrants. To access the posterior quadrant a lateral rotation of the patient is often necessary. Dressings and tubes may limit access to all quadrants in the ICU setting. Fig 2 Patient positioning, lung fields, probe orientation Standard view Normal lung The lung is scanned using Brightness (B) mode and Motion (M). The upper portion of the US image (near field) displays objects close to the probe, the lower portion (far field) objects that are away from the probe. In normal lung (Fig 3) a bright longitudinal line (pleural line) is identified cm from the origin of the rib acoustic shadow (dark cone) and corresponds to the parietal pleura. Shimmering of the pleural line during inspiration constitutes the sliding lung and corresponds to the sliding of the parietal and visceral pleura. This feature is not observed in case of pneumothorax. Equidistant parallel longitudinal lines (A lines) can be easily noticed and constitute a reverberation artifact. In the lateral quadrant it is normal to observe perpendicular lines (B lines) originating from the pleural line, crossing the far field and moving with the sliding lung. However, when noticed in the anterior quadrants this may indicate pulmonary edema or pneumonia. M mode demonstrates the 3

4 typical seashore sign determined by grainy far-field (sand) and sudden transition to a parallel line in the near-field (sea). Fig 3 Normal Lung P, pleural line; A, A line. Pneumothorax Lung US can detect pneumothorax with a sensitivity of 91% (Chest X Ray: 50.2%) and a specificity of 98%. US feature of a pneumothorax (Fig 4) include all of the following: Absent lung sliding (stratosphere sign on M Mode) A lines Lung Point The lung point determines the limits of the pneumothorax. When observed in the anterior fields, it likely indicates small pneumothorax. However, when observed in the posterior fields, it may indicate a large pneumothorax likely requiring drainage. Lack of sliding lung alone is not sufficient to make a diagnosis of pneumothorax and can be observed with: apnea, main stem bronchial intubation, main stem bronchial obstruction, pleural adhesion and large infiltrates. Fig 4 Pneumothorax A, Stratosphere sign; B, Lung point (arrow). Pleural effusions Lung US demonstrated a sensitivity of 92% (Chest X Ray: 57%) and specificity of 93% detect pleural effusions. Pleural effusion presents as a hypoechoic (dark) area roughly quadrangular 4

5 (Quad sign) delimited by the chest wall and the atelectatic lung (Fig.5). On M mode, the movement of the edge of the lung reveals a sinusoidal line. Lung US allows determination of effusion location, presence of septations, differentiation of transudate and exudate (spontaneous echo-contrast within the effusion: plankton sign) and estimation of volume. Finally, lung US may be used to guide thoracentesis and positioning of a chest tube, decreasing complications by 15%. For this reason the use of US for thoracentesis and chest tube insertion has become part of latest guidelines of the British Thoracic Society. Fig 5 Right Pleural Effusion D, Diaphragm; S, Spleen, * Effusion; L, lung; Arrow, atelectasis; M Mode arrow, sinusoid sign. Other Clinical applications Recognition of different patters based on A lines, B lines, sliding lung and consolidation has been successfully used in the diagnosis of respiratory failure. The ability to detect ventilation by identifying sliding lung proved lung US has proven to a be a quick and very accurate instrument to assess bilateral ventilation after intubation in the emergency setting. Suggested Readings 1. Alrajhi K, Woo MY, Vaillancourt C. Test Characteristics of Ultrasonography for the Detection of Pneumothorax: A Systematic Review and Meta-analysis. Chest. 2011, Aug 25 E pubahead of print 2. Beckh S, Bolcskei PL, Lessnau KD. Real-time chest ultrasonography: a comprehensive review for the pulmonologist. Chest Nov;122(5): Havelock T, Teoh R, Laws D, Gleeson F. Pleural procedures and thoracic ultrasound: British Thoracic Society Pleural Disease Guideline Thorax. Aug;65 Suppl 2:ii Lichtenstein DA. Ultrasound examination of the lungs in the intensive care unit. Pediatr Crit Care Med Nov;10(6): Lichtenstein DA, Meziere GA. Relevance of lung ultrasound in the diagnosis of acute respiratory failure: the BLUE protocol. Chest Jul;134(1): Mayo PH, Beaulieu Y, Doelken P, Feller-Kopman D, Harrod C, Kaplan A, et al. American College of Chest Physicians/La Societe de Reanimation de Langue Francaise statement on competence in critical care ultrasonography. Chest Apr;135(4): Sim SS, Lien WC, Chou HC, Chong KM, Liu SH, Wang CH, et al. Ultrasonographic lung sliding sign in confirming proper endotracheal intubation during emergency Intubation. Resuscitation 2011, Nov 29 Epub ahead of print. 5

Pleural Ultrasonography

Clin Chest Med 27 (2006) 215 227 Pleural Ultrasonography Paul H. Mayo, MD a, T, Peter Doelken, MD b a Albert Einstein College of Medicine, Bronx, NY, USA b Division of Pulmonary, Critical Care, Allergy,