How do I perform and interpret a FAST exam in a trauma or dyspneic small animal patient?

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Global Focused Assessment with Sonography for Trauma (Global FAST) combines abdominal FAST (AFAST), thoracic FAST (TFAST), and Vet BLUE into a single 15-point point-of-care ultrasound examination performed cageside as an extension of the physical exam. It is low-impact, radiation-sparing, requires no shaving, and provides real-time information on free fluid and soft tissue abnormalities of the abdomen, heart, and lung that are missed or only suspected by physical examination, blood work, and radiography.13 Before imaging, the dyspneic patient requires immediate clinical stabilization. Oxygen is administered immediately via flow-by, mask, hood, nasal, or oxygen cage techniques.2 Stressful procedures — including radiographs — can cause rapid decompensation in the respiratory patient, so thoracic radiography is performed only when the animal can tolerate it and must not delay therapy.2 Global FAST is specifically advantageous here because it is cageside and low-impact, making it safer than radiography in the unstable patient.3 TFAST evaluates the pleural space and pericardium. In the dyspneic patient, TFAST screens for pleural effusion, pneumothorax, and pericardial effusion, and includes assessment of the left atrial to aortic ratio — a ratio below 1.7 is normal.5 Diffuse coalescing B-lines bilaterally on TFAST indicate pulmonary parenchymal disease rather than pleural space disease.5 Distinguishing pleural space from parenchymal disease is clinically critical because it directs therapy: pleural space disease is treated with thoracocentesis, while parenchymal disease is treated with oxygen supplementation and sedation directed at the underlying cause.2 TFAST reliably detects pleural free fluid but is not a reliable method to diagnose pneumothorax. Agreement between TFAST and CT for pleural effusion detection is fair to moderate. Agreement between TFAST and CT for pneumothorax detection is poor.6 When pneumothorax is a primary concern following trauma, CT is the defini