Absolutely. Though costophrenic blunting may not be seen on a PA or AP chest radiography until more than 200 mL of pleural effusion is present, as little as 20 mL of pleural fluid can be reliability detected with POCUS, with a sensitivity of 100% when more than 100 mL is present. Most pleural effusions will accumulate in the dependent areas within the chest cavity. Thus, in the usual semi-recumbent position used for POCUS, pleural effusion will accumulate above the diaphragm and below the lower lobe of the lungs.1,2
Few things to consider when evaluating for pleural effusion.
- Because evaluation for pleural effusions may require imaging depths of 10 to 20 cm, low frequency (preferably a phased array) transducer should be used.
- Place the transducer in the posterior axillary line around the level of the diaphragm with the orientation marker positioned cephalad in the coronal plane (FIGURE 1).
- Identify the diaphragm and use it as a point of reference to minimize mistakes such as labeling ascites as pleural effusion. Structures above the diaphragm (atelectatic lung, pleural effusion) will be shown on the left while structures below the diaphragm (abdominal organs, ascites) will be shown on the right side of the ultrasound display (FIGURE 2).
- Keep in mind that freely flowing atelectatic lung tip (jellyfish sign) and spine shadows (spine sign) may be visible (VIDEO 1). Anechoic, free flowing pleural effusions are categorized as simple while homogeneously and heterogeneously echogenic effusions or those with septations are categorized as complex (VIDEO 2 and VIDEO 3). 2,3
- Smaller effusions may be seen as a small anechoic layer of fluid between the chest wall and the lung. If you use the M-mode, you will find that the lung moves towards or away from the chest wall in a wave like pattern (sinusoid sign) (VIDEO 4).1
Bonus Pearl: Did you know that you can estimate pleural effusion volume by using the following formula: Volume=16 x distance from mid lung base to the diaphragm (mm)? 4
Contributed by Woo Moon, D.O, Director, Hospitalist and Internal Medicine Residency Point-of-Care Ultrasound Programs, Mercy Hospital-St. Louis, St. Louis, Missouri
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Figure 1 Figure 2
Figure 3
Video 1
Video 2
Video 3
Video 4
References
- Soni NJ, Arntfield R, Kory P. Point of Care Ultrasound. 2nd ed. St. Louis, MO: Elsevier; 2019.
- Soni NJ, Franco R, Velez MI, et al. Ultrasound in the diagnosis and management of pleural effusions. J Hosp Med 2015;10(12):811–6. Ultrasound in the diagnosis and management of pleural effusions – PubMed (nih.gov)
- Yang PC, Luh KT, Chang DB, Wu HD, et al. Value of sonography in determining the nature of pleural effusion: analysis of 320 cases. AJR Am J Roentgenol 1992;159(1):29–33. Value of sonography in determining the nature of pleural effusion: analysis of 320 cases – PubMed (nih.gov)
- Usta E, Mustafi M, Ziemer G. Ultrasound estimation of volume of postoperative pleural effusion in cardiac surgery patients. Interact Cardiovasc Thorac Surg 2010;10(2):204–7. Ultrasound estimation of volume of postoperative pleural effusion in cardiac surgery patients – PubMed (nih.gov).
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