Rajesh Geria, M.D., RDMS
I. Introduction and Indications
One of the many etiologies of dyspnea in the emergency department is a pleural effusion. A pleural effusion is an abnormal collection of fluid in the pleural space. Removal of this fluid by needle aspiration is called a thoracentesis. Although Xray can be obtained relatively easily it has been shown to be less sensitive than ultrasound for detecting smaller effusions. In addition, ultrasound can precisely identify the location of the fluid so that the chest wall can be marked in preparation for thoracentesis. (1) Thoracentesis can be both diagnostic and therapeutic for the patient. Using ultrasound to guide this procedure can decrease the very high complication rate associated with it. (1-3)
- Therapeutic intervention in symptomatic patient
- Diagnostic evaluation of pleural fluid
The pleural space is bordered by the visceral and parietal pleura. Fluid in the pleural space appears anechoic and is readily detected above the brightly echogenic diaphragm when the patient is in a supine position.
Figure 1: Showing a large pleural effusion, diaphragm and liver.
III. Scanning Technique and Pathology:
The ideal position for the patient is to sit upright leaning forward. A high frequency linear transducer (7.5 to 10 MHz) is the optimal choice for this procedure and placed on the patient’s back in the sagittal or transverse position (Figure 2). The lung is seen as an echogenic structure moving with respiration. Look for the deepest pocket of fluid superficial to the lung. The image is frozen and a measurement should be taken to approximate the depth the needle will have to be inserted to reach the maximum amount of fluid (Figure 3).
Figure 2: Shows patient in sitting position with ultrasound probe placed over the thoracentesis area.
Figure 3: Muscle, fluid, lung, and measurements.
Illustration 2: Overview of technique.
Since the ultrasound beam must penetrate the chest wall in order to image the effusion you will see ribs. The edge of the bone is echogenic and gives off a characteristic shadowing (Figure 4). The area should be marked with a pen and then prepped and draped in standard surgical fashion before the procedure is performed.
Figure 4: Pleural effusion with rib shadow. The transducer is placed perpendicular to the axis of the rib.
Video clip 1: This video shows the thoracentesis location before needle insertion.
Complications can include pneumothorax, puncture of lung tissue, cystic masses, empyema or mediastinal structures.
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