Introduction

Thoracentesis is a common procedure that is used for both diagnostic evaluation and symptomatic treatment of large pleural effusions and suspected empyemas in the emergent setting. Pleural effusions are the most common sequelae of pleural disease, usually due to cardiogenic, inflammatory or infectious disorders. A procedure performed by emergency physicians, critical care intensivists, and hospitalists, it can be done safely and successfully with the use of bedside ultrasound (US) and proper training.¹ In fact, ultrasound guided thoracentesis has been shown to decrease hospital stay, cost, and complications such as hemorrhage and pneumothorax when used appropriately².

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Learning Objectives

After reading this article, the physician should be able to:

• Understand the benefits and limitations of using ultrasound for thoracentesis
• Identify structures with the use of ultrasound to efficiently perform thoracentesis and limit its complications

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In addition to identifying and quantifying the amount of pleural fluid present, there have been a few studies utilizing ultrasound to distinguish transudative versus exudative pleural effusions. Hirsch, et al found that complex and septated fluid was correctly identified as an exudative process via ultrasonography in 74% of cases³.

However, Yang, et al determined that complex effusions (either septated or non-septated) or homogeneously echoic effusions are always exudative⁴. The converse, however, may not be true and thus anechoic fluid, although usually transudative, can be either transudative or exudative. In order to correctly correlate ultrasonographic characteristics of effusions, more experience is needed beyond the ability to identify the presence of pleural fluid and thus is beyond the scope of this article.

Needle or catheter drainage of pleural effusions can be performed using fluoroscopy, ultrasound, or computed tomography (CT) scanning. Ultrasound’s advantage over CT includes its easier accessibility and non-ionizing radiation. It’s also less expensive than CT and much quicker to perform than CT guided drainage⁵.

It is also more logistically feasible to perform US at the bedside in critically ill patients who might be mechanically ventilated or too ill to be moved from the emergency department or intensive care unit^5,6. Free-flowing pleural effusions are also much easier to target while using US, as they trek to the most dependent areas of the thorax – a much more difficult location to target using CT⁵.

Ultrasound guided thoracentesis has been proven to reduce the incidence of complications such as pneumothorax, which has been reported to be as high as 20 to 39%⁷. To date there have been no randomized, controlled trials comparing ultrasound-guided versus physical examination-guided thoracentesis. Grogan, et al found a 29% reduction in the pneumothorax rate when ultrasound was utilized for identification of needle placement⁷. Even when a pneumothorax does occur, the incidence of pneumothorax requiring tube thoracostomy is also significantly reduced with ultrasound guidance⁸. Ultrasound also reduces the number of unsuccessful clinical attempts at thoracentesis (“dry tap”), because more than 50% of needle insertions are below the diaphragm⁹. Ultrasound increased the accuracy of site selection by approximately 26% and decreased the number of near misses in a study by Diacon et al.¹⁰.