Although the image detail may be somewhat less with

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Although the image detail may be somewhat less with the lower-frequency probe, sliding or its absence is still readily detectable. First, identify the rib shadow. This allows you to locate the intercostal plane. Next, identify the pleural line. This is the hyperechoic line located between and below two ribs. In the normal subject, this pleural line is characterized by lung sliding. You should also look for comet tail artifacts as seen in Figures 2.44 and 2.45 . Normal lung sliding and the presence of the comet tail artifact rule out pneumothorax with a 100% negative predictive value ( Table 2.1 ). Figure 2.43 Anterior positioning of probe on chest wall ( left ), and anterior axillary-line positioning ( right ). Greater lung sliding is usually seen with axillary-line probe positioning because of greater lung excursion with respirations at this level. However, the anterior position is more sensitive in the supine patient because air layers anteriorly. Courtesy of Dr. Greg Press, University of Texas – Houston, Hermann Memorial Hospital, Houston, TX. 52 Diagnostic ultrasound Focused assessment with sonography in trauma (FAST)
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There are three ways to assess the presence of lung sliding using ultrasound. First, the lung slide can be directly observed in real time using two-dimensional ultrasonography, and images can be saved as video. Second, power Doppler can be used to highlight the motion of the pleura. Positive and negative Doppler images are demonstrated in Figure 2.46 . Third, M-mode can be used to demonstrate lung sliding on a static image. When using M-mode for this technique, follow a line that includes subcutaneous tissue, chest wall musculature, pleura, and lung and make sure to avoid Figure 2.44 Longitudinal scan of the anterior chest wall of a normal patient. The “pleural line” and a comet tail artifact are labeled. The normal to-and- fro sliding movement of this pleural line, synchronized with the respiratory cycle, can be observed in real time. Figure 2.45 Here you can see the rib shadow, pleural line, and comet tail artifact of a normal lung image. Diagnostic ultrasound 53 Focused assessment with sonography in trauma (FAST)
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placing the M-mode line over a rib. In a normal lung, the image obtained using M-mode should demonstrate smooth lines superficially (because the chest wall should not move much with respiration in this view). Deep to the pleura, the sliding lung will produce enough motion artifact to create Table 2.1 Literature support for ultrasound diagnosis of pneumothorax Reference Feature Performer Probe Patients Standard Sens Spec NP PP Blaivas et al . 2005 [ 30 ] LS ED 176 blunt trauma CT 98 99 99 98 Rowan et al . 2002 [ 24 ] LS, comet tail Radiology 7.0 MHz 27 ED trauma getting CT CT 100 94 100 92 Dulchavsky et al . 2001 [ 31 ] LS, comet tail Surgery 4.0 Mhz 382 trauma CXR 94 100 99.4 95 Lichtenstein et al . 1999 [ 32 ] LS, comet tail ICU 3.5 MHz 115 ICU CXR, CT 100 96.5 100 89 Lichtenstein et al . 1995 [ 33 ] LS ICU 3.0 MHz 111 hemitho- races in ICU CXR, CT 95.3 91.1 100 87 LS, lung sliding; ED, emergency department; ICU, intensivist; Sens, sensitivity; Spec,
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