Procedural ultrasound 299 ultrasound for procedure

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Procedural ultrasound 299 Ultrasound for procedure guidance
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Tips Measuring the depth from the skin to the parietal pleura allows for needle entry to a depth that should yield fluid while lowering the risk of puncturing the visceral pleura. Pitfalls Observe the proposed puncture site during the entire respiratory cycle. Significant changes in diaphragm position occur during respirations. Literature review Ultrasound was first used as a rescue method for failed or difficult thoracent- esis. One early study demonstrated ultrasound-guided thoracentesis was successful in 88% of previously failed landmark-based attempts. The authors noted that scanning over the initial attempt sites found it to be above or below the effusion in 69% of the cases, and that the initial attempt was directly over the spleen, liver, or kidney in 58% of the cases [ 2 ]. Ultrasound guidance has a high success rate, even in cases where no fluid is visible on chest x-rays [ 3 ]. More recently, a study by interventional radiologists demonstrated a low complication rate (2.5% pneumothorax) when using ultrasound gui- dance, compared to historic pneumothorax rates of 4–30%. Interestingly, this study also noted that complications were not correlated to the amount of fluid removed during the procedure [ 4 ]. A retrospective study of ultrasound Figure 16.4 Thoracentesis setup. Note that needle placement and patient position are the same as for a standard landmark-based technique. 300 Procedural ultrasound Ultrasound for procedure guidance
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guidance versus landmark-based techniques demonstrated a significantly lower pneumothorax rate in the ultrasound guidance group (4.9% vs. 10.3%) [ 5 ]. Ascites and paracentesis Detection of ascites by ultrasound is useful in the patient presenting with abdominal distension. Many patients without a known history of ascites present with abnormal transaminase levels and distension, and the presence of ascites is often incorrectly assumed. Beyond the diagnostic utility in confirming the diagnosis, ultrasound is helpful in choosing the optimal site for paracentesis. Focused questions 1. Is there free fluid (ascites) in the abdomen? 2. Where is the optimal location for paracentesis? Anatomy Ascites accumulates in a gravity-dependent fashion within the peritoneum, similar to blood in trauma, as discussed in Chapter 2 . Unless prior surgery, infections, or scarring alter the anatomy, the fluid tends to be free flowing. If loculations are present, the location of fluid pockets will be highly variable, and bowel may not “float” in the ascites as it normally would. Technique Probe selection Ultrasound of the abdomen may be performed with a 2.5–5.0 MHz transducer. Special equipment A marking pen may be used. Setup Place the patient in the normal preferred position for paracentesis. Some authors prefer a decubitus position, while others have the patient sitting upright. The ultrasound technique employed is similar to that used in the FAST examination. In addition to the left and right upper quadrant exam,
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