Today's Veterinary Practice

NOV-DEC 2018

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PEER REVIEWED 58 NOVEMBER/DECEMBER 2018 todaysveterinarypractice.com The AFAST examination can be performed with the patient in one lateral position. A complete TFAST examination is performed with the patient in alternating left and right lateral recumbency or in sternal recumbency. Dyspneic patients should be provided with supplemental oxygen and should be scanned in sternal recumbency. AFAST and TFAST examinations should never be prioritized over immediate life-saving therapy. Image optimization requires a basic understanding of the ultrasound machine controls. For a given window, image depth and focus are optimized first. The gain (2D) is generally set at 70% (depending on the company and machine) to create an image that can be viewed in a room with high ambient lighting. B-mode or 2D grayscale ("brightness") mode ultrasonography is used, and different echogenicities are represented by relatively bright/white (hyperechoic) and relatively dark/black (hypoechoic) shades of gray, between the two extremes of white and black. The darkest, most hypoechoic extreme is termed anechoic, meaning "without echoes," and is typical of fluids (transudate, modified transudate, and some types of exudate). INTERPRETATION OF COMMON FINDINGS Cavitary effusions, when present, are often found adjacent to viscera and appear anechoic, although the cellular, lipid, or protein content can increase fluid echogenicity. Ultrasound alone cannot reliably determine the constitution or etiology of effusions. Echogenic material in the fluid does not equate with an exudate; anechoic fluid or echogenic fluid can be a transudate, modified transudate, or exudate. Cavitary effusions in small animals vary in etiology ( BOX 1 ). When a cavitary effusion is identified and sampling is clinically indicated, standard procedures for paracentesis should be used as long as there are no contraindications to sampling (i.e., thrombocytopenia or coagulopathy of any form). 6 In human emergency medicine, thoracic ultrasonography has been shown to be a rapid and accurate test for identifying pneumothorax. 7 Correctly identifying pneumothorax, however, requires the ability to distinguish reverberation artifact—which is created when the ultrasound beam encounters gas within the pleural space— from the typical normal pattern of a glide motion seen within the lung (see TFAST Techniques). AFAST TECHNIQUE The technique for performing the AFAST examination is described in detail elsewhere. 1–3 Four acoustic "windows" are assessed in a complete AFAST examination ( FIGURE 1 ). At each window, compose the image so that the machine company logo is on BOX 1 Considerations for Cavitary Effusions Peritoneal effusion Hemoabdomen (e.g., neoplasia, hematoma, trauma ) Transudates (e.g., hypoproteinemia, portal hypertension) Septic exudates (e.g., rupture of hollow viscus or abscess, ruptured gallbladder) Variable (e.g., neoplasia, renal disease, feline infectious peritonitis) Uroabdomen Chylous effusion Pleural effusion Congestive heart failure Neoplasia Hemorrhage Chylous effusion Pericardial effusion Hemorrhage from heart base neoplasm Idiopathic pericardial effusion Chylous pericardial effusion Left atrial tear FIGURE 1. Locations for the 4 AFAST windows, shown with patient in right lateral recumbency. For each window, an examination should be performed with the ultrasound probe in a long and short axis relative to the patient. The HR probe image has decreased opacity because to obtain images, the probe must be placed underneath the dog or cat and directed dorsally and cranially at the level of the 13th rib. If stable, the patient can be turned over so that the left side is down and right side is up. CC, cystocolic window; DH, diaphragmatic-hepatic window; HR, hepatorenal window; SR, splenorenal window.

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