In figure 1628 the needle is visualized as the

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In Figure 16.28 , the needle is visualized as the abscess cavity is drained. As with vessel cannulation, static localization or dynamic cavity aspiration is possible and may depend on the patient’s ability to tolerate continuous ultrasound imaging. Figure 16.27 A peritonsillar abscess is seen in the near field (small white arrows), and the carotid artery is visualized in the far field (large red arrow). Figure 16.28 Peritonsillar abscess drainage via needle aspiration (arrows). Image courtesy of Dr. Michael Blaivas, Professor of Emergency Medicine, Northside Hospital Forsyth, Atlanta, GA. 318 Procedural ultrasound Ultrasound for procedure guidance
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Literature review Ultrasound is more accurate than physical exam alone in detecting abscess (positive predictive value 93% vs. 81%; negative predictive value 97% vs. 77%) [ 16 ]. Thus, the number of non-therapeutic incision and drainage pro- cedures could be reduced using ultrasound guidance. Another study of soft- tissue infections in the emergency department demonstrated that ultrasound changed the management of nearly 50% of patients. Management changes included recognition of occult abscess where only cellulitis was expected, deferring incision and drainage where no abscess was found, and obtaining further diagnostic studies or consultation [ 17 ]. In the setting of possible peritonsillar abscess, ultrasound has demon- strated promise in preliminary studies. One study demonstrated nega- tive aspirates in three patients without abscess identified on ultrasound, and positive aspirates in three patients with sonographic findings of abscess [ 18 ]. Lumbar puncture One of the classic landmark-guided procedures, lumbar puncture, can be quite challenging in patients without classic landmarks. In many emergency department patients, spinous processes are not readily palpable, and it is not uncommon for the iliac crests to be obscured by certain body proportions as well. Ultrasound can be used to locate the orientation and depth of the spinous processes, which can be a huge advantage for a critical diagnostic procedure. Focused questions 1. Where is the interspinous space? 2. How deep is the interspinous ligament? Anatomy The goal of lumbar puncture (using a midline approach) is to place the needle through the skin and subcutaneous tissues, into the interspinous ligament, through the ligamentum flavum, and into the subarachnoid space. Ultra- sound can demonstrate much of the target anatomy. In some patients, the ligamentum flavum can be visualized, but more commonly, at least the spinous processes are well visualized on ultrasound. Technique Probe selection Ultrasound can be performed with a high-frequency (5–10 MHz) linear probe or a lower-frequency (2–5 MHz) curvilinear probe. Procedural ultrasound 319 Ultrasound for procedure guidance
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Special equipment A marking pen is used.
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