Thoracic FAST scan (TFAST) is used to look for evidence of pleural effusion, pericardial effusion, pulmonary ­disease, and pneumothorax. In a prospective study of 49 cats, the TFAST scan was found to have a sensitivity and specificity for detecting pneumothorax of 62.5% and 100%, respectively, compared with thoracic radiography.5 Differences are noted in sensitivity depending on operator experience level.

The patient can be in sternal or in lateral recumbency, preferably sternal if having respiratory difficulty. The modified five-point protocol includes the original four points of evaluation and the additional abdominal FAST (AFAST) diaphragmatic–hepatic (DH) site (Fig. 10.6).⁴ The first site of evaluation is the chest tube site, which is at the 7th–9th intercostal space on the dorsolateral thoracic wall. The probe is held horizontally and evaluated for evidence of a glide sign. Normally the lungs glide back and forth across the chest wall. This produces a hyperechoic horizontal line on ultrasound known as the glide sign (Fig. 10.7). The negative predictive value of TFAST is high so that presence of a glide sign rules out pneumothorax.⁶ The pericardial site, at the 5th–6th intercostal space on the ventrolateral thoracic wall, is evaluated for pleural or pericardial effusion. The probe is held in both transverse and longitudinal views. Hyperechoic vertical lines, or comet tail artifacts known as B-lines, are increased in number when pulmonary edema is present (Fig. 10.8). B-lines move in a to-and-fro fashion with inspiration and expiration. An occasional B-line is considered normal but multiple B-lines suggest interstitial–alveolar lung abnormality. Lastly, the diaphragmatic–hepatic site is just caudal to the xiphoid process and is used to evaluate for pleural and pericardial effusion when the probe is angled towards the heart. The probe is held in both transverse and longitudinal views. This site has been shown to have excellent sensitivity and specificity for pleural and pericardial effusion in humans but since the heart does not reliably rest on the diaphragm in animals as it does in humans, this site has its limitations in veterinary patients.⁴

Abdominal FAST (AFAST) is used to quickly rule out the presence of free abdominal fluid and for serial assessment to detect changes in fluid accumulation. Although excellent for detecting free fluid, AFAST is not sensitive for localizing the site of injury responsible for the fluid accumulation.6 A negative scan does not rule out abdominal injury. Repeat examinations should be performed every 2–4 hours or as needed if the patient is unstable.

The four-point AFAST is generally performed in right lateral recumbency but can be done in standing position. Right lateral recumbency is preferred since it is the standard position for electrocardiogram (ECG) evaluation. Iatrogenic puncture of the spleen during abdominocentesis is less likely in this position since the spleen lies more to the left of the midline.⁴ The abdomen is scanned in a clockwise fashion for free fluid in four regions (Fig. 10.9): DH (caudal to the xiphoid process), spleno-renal (SR; left flank), cysto-colic (CC; midline over the urinary bladder), and hepato-renal (HR: right flank).⁴ These regions allow visualization of the diaphragm, liver, gall bladder, spleen, kidneys, intestinal loops, and urinary bladder. Free fluid accumulates in the most dependent areas of the abdomen and is seen as anechoic triangles.⁶ The DH view evaluates the liver lobes, gallbladder, and the area between the liver and the diaphragm (Fig. 10.10). This view is also used to evaluate the pericardial sac and pleural spaces as noted in the TFAST procedure. The SR view evaluates the spleen and left kidney (Fig. 10.11). The CC view evaluates the apex of the bladder (Fig. 10.12). The HR view evaluates the liver, right kidney, and areas between loops of intestines (Fig. 10.13). A diagnostic abdominocentesis can be performed if free fluid is visualized.

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