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Emergency Ultrasound

The Use of Lung Ultrasound in the Critical Care and Emergency Settings to Identify Pleural Effusions

Vi Am Dinh 2016Vi Am Dinh, MD, RDMS, RDCS
Department of Medicine, Division of Pulmonary and Critical Care
Loma Linda University, Loma Linda, California, USA

Whitney Anne Hampton, MD
Department of Emergency Medicine
Loma Linda University, Loma Linda, California, USA

Corresponding Author:
Vi Am Dinh, MD, RDMS, RDCS
Loma Linda University Medical Center
11234 Anderson Street, A108
Loma Linda, CA 92354, USA
Phone Number: (909) 558-4000 ext 82310, Fax: (909) 558-0121

Keywords: Critical Care, Lung Ultrasound, Pleural Effusions

Lung ultrasonography is a sensitive and specific bedside test to detect pleural effusions in critically ill patients. The technique to detect pleural effusions, as well as terminology of common findings within pleural effusions is discussed. One method of measuring and quantifying pleural effusions is provided.

Pleural effusions in the critical care setting are common, with a reported prevalence of 62%.1 Pleural effusions develop for a variety of reasons in the critically ill, most often due to heart failure or atelectasis.1 Traditionally, chest radiography has been used to detect pleural effusions and other intrathoracic pathology. Lung ultrasonography has been shown to be superior to chest radiography in the detection of pleural effusions with a sensitivity and specificity of 92% and 93%, respectively.2,3 Lung ultrasonography is also better able to differentiate between effusion and consolidation when an opacification is seen on a supine chest radiography.3 It can also be better at visualizing septations in fluid collections compared to Computed Tomography.4 Lung ultrasonography can assist the examiner in procedures such as thoracenteses. It is clear that the ability to perform a bedside lung ultrasound for pleural effusions in the critical care setting has a number of benefits.

Lung ultrasonography is best performed using a phased array or microconvex transducer.3 To detect pleural effusions in a supine patient, the longitudinally orient the transducer longitudinally with the indicator pointed towards the patient’s head in the posterior axillary line between the 10th and 11th ribs on the right, and the 9th and 10th ribs on the left.5,6 The thoracic cavity is evaluated by identifying the diaphragm as the curvilinear hyperechoic line that moves with respiration, and then sliding the transducer towards the patient’s head.5 A pleural effusion has an anechoic appearance often delineated by the pleural line, the rib shadows, and the lung line, called the quad sign,7 Figures 1a and 1b. One should also see a sinusoidal pattern on M-mode as the lung line moves with respiration in relation to the pleural line7 An anechoic fluid collection is often a transudative effusion, whereas a heterogeneous fluid collection is typically an exudative effusion.5 Dynamic swirling debris commonly seen in exudative effusions is called the plankton sign,5 Figure 2. Highly cellular effusions may appear on static imaging as layered as cells collect in a dependent fashion by gravity, termed the hematocrit sign,5 Figure 3. With large pleural effusions, one may identify compressed, airless lung floating within the effusion, termed the jellyfish sign,5 Figure 4. It is important to adjust the depth setting on the ultrasound machine to define the boundaries of the pleural effusion.5 Large pleural effusions may be confused as pericardial effusions on bedside cardiac ultrasound scanning, and it is important to adjust the depth of the probe to identify the descending thoracic aorta, as pleural effusions are posterior to the descending aorta and pericardial effusions are anterior,8 Figure 5.

Many studies have been published regarding formulas to measure and quantify a pleural effusion, though no consensus has been formed.9 One method proposed by Balik et al10 involves rotating the probe to a transverse orientation and obtaining the maximal separation measurement in millimeters between the two pleural layers at the lung base, termed the Sep measurement, Figure 6. This value is multiplied by a factor of 20 to obtain volume of pleural fluid: V(mL) = 20 x Sep (mm). The measurement and quantification of pleural effusions may aid in the decision to perform a thoracentesis, as approximately 200ml is a safe minimum volume.

The use of bedside lung ultrasonography to detect and evaluate pleural effusions should be routinely used in the critical care setting. Quantification of the pleural effusion may assist in clinical decision-making and need for thoracentesis.


  1. Mattison LE, Coppage L, Alderman DF, et al. Pleural effusions in the medical ICU: prevalence, causes, and clinical implications. Chest. 1997;111(4):1018-1023.
  2. 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(1):9-15.
  3. Volpicelli G, Elbarbary M, Blaivas M, et al. International evidence-based recommendations for point-of-care lung ultrasound. Intensive Care Med. 2012;38(4):577-591.
  4. McLoud TC, Flower CD. Imaging the pleura: sonography, CT, and MR imaging. AJR American journal of roentgenology. 1991;156(6):1145-1153.
  5. Mayo PH, Doelken P. Pleural ultrasonography. Clin Chest Med. 2006;27(2):215-227.
  6. Rozycki GS, Pennington SD, Feliciano DV. Surgeon-performed ultrasound in the critical care setting: its use as an extension of the physical examination to detect pleural effusion. J Trauma. 2001;50(4):636-642.
  7. Xirouchaki N, Kondili E, Prinianakis G, et al. Impact of lung ultrasound on clinical decision making in critically ill patients. Intensive Care Med. 2014;40(1):57-65.
  8. Noble VE, Nelson B, Sutingco AN, Ebooks Corporation.: Manual of emergency and critical care ultrasound, First edition. edn.
  9. Cantinotti M, Giordano R, Volpicelli G, et al. Lung ultrasound in adult and paediatric cardiac surgery: is it time for routine use? Interact Cardiovasc Thorac Surg. 2015.
  10. Balik M, Plasil P, Waldauf P, et al. Ultrasound estimation of volume of pleural fluid in mechanically ventilated patients. Intensive Care Med. 2006;32(2):318-321.

Figure 1a. Quad sign without labels.
Quad Sign Without Labels  

Figure 1b. Quad sign with labels. 

Quad Sign With Labels

Figure 2. Plankton Sign.
YouTube link: https://www.youtube.com/watch?v=WDxxJVqWrQE

Figure 3. Hematocrit Sign. 
Hematocrit Sign

Figure 4. Jellyfish Sign.
YouTube link: https://www.youtube.com/watch?v=xHWrgKk4q5o

Figure 5. Differentiating pleural effusion from pericardial effusion.
YouTube link: https://www.youtube.com/watch?v=vVRALoZQVl4

Figure 6. Maximal separation measurement at lung base 
Max Separtation at Lung Base


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