Anatomy fluid accumulates between the visceral and

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Anatomy Fluid accumulates between the visceral and parietal layers of the pleura. It collects in the most dependent portions of the pleura (the costophrenic angles) and rises from that level as more volume accumulates. One of the first signs of pleural fluid is the loss of the normal mirror image artifact caudal to the diaphragm and liver or spleen. In Figure 16.1 the liver, kidney, dia- phragm, pleural fluid, and lung are all visible. Technique Probe selection Ultrasound of the pleural space may be performed with a 2.5–5.0 MHz transducer. Special equipment A marking pen is useful for many procedures where ultrasound mapping and static guidance is used ( Figure 16.2 ). Kidney Liver Diaphragm Pleural Fluid Figure 16.1 Black pleural fluid is demonstrated superior to the diaphragm and liver. The kidney is also well visualized in this view. Figure 16.2 Marking pen. 298 Procedural ultrasound Ultrasound for procedure guidance
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Setup The patient is positioned in a seated-upright position when possible. Scanning is performed from the anterior axillary line to the paravertebral space and from the superior and inferior aspects of the fluid collection. The feasibility of thoracentesis requires the demonstration of a sonographic window to the fluid persisting throughout the respiratory cycle. There is no formal lower limit of effusion size beneath which thoracentesis is contraindi- cated. However, many operators recommend that a visceral to parietal pleural distance of at least 10 mm is preferable to minimize the risk of an adverse outcome. Moreover, incursions of lung or diaphragm during the respiratory cycle into the sonographic window are considered absolute contraindications to thoracentesis at that site. Positive identification of the diaphragm plus liver or spleen is required to avoid puncture of these organs. If no safe sonographic window is identified, seriously consider aborting the procedure. After identifying a suitable sonographic window, note the angle of the transducer. In addition, measure the depth required to achieve penetration into the pleural space containing fluid ( Figure 16.3 ). Last, mark the skin at the site of planned needle entry. Procedure Immediately following ultrasound examination, prepare the site in a ster- ile fashion and perform thoracentesis in the usual fashion ( Figure 16.4 ), taking care not to alter the patient’s position. Duplicate the angle of the transducer with the thoracentesis needle or catheter during the procedure. Direct visualization of needle entry is not necessary if the prior steps are followed. Lung * Liver D Figure 16.3 Pleural fluid (*) is noted above the diaphragm (D) and liver. Lung tissue is normally not well visualized because of the large amount of air. In this case the pleural fluid provides a good acoustic window, and the normally aerated lung tissue has been compressed somewhat and made more dense by the additional fluid pressureinthethorax.
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