In the supine patient, free fluid from the right upper quadrant (RUQ) will tend to collect in Morison pouch first, whereas free fluid from the left upper quadrant (LUQ) will often accumulate in the left subphrenic space initially (i.e., not the splenorenal recess) The amount of intraperitoneal fluid needed for detection by ultrasound has been reported to be as little as 100 mL in adults and will depend on the source of the bleeding and patient positioning Technique Probe selection is the first step A low-frequency (2 to MHz) probe should be chosen for adequate penetration, most commonly a large footprint curvilinear probe In pediatric trauma, however, the smaller head of a phased array probe or microconvex probe may be more useful to obtain images between the small intercostal spaces There are four views of the FAST examination: (a) hepatorenal recess or Morison pouch, (b) splenorenal recess, (c) pelvic/bladder view, and (d) subxyphoid pericardial view (Fig 131.6 ) Many practitioners also incorporate views of the thorax to assess for hemothorax or pneumothorax, referred to as the enhanced FAST or eFAST The sonographer should perform the FAST examination in a systematic manner in a standard sequence This will allow greater focus on image acquisition and optimization as the examination order becomes routine A view of Morison pouch can be obtained by placing the probe in the coronal plane (marker toward the patient’s head) in the anterior axillary line between the seventh and ninth ribs on the patient’s right-hand side If rib shadows prevent optimal images, the probe can be rotated slightly in a counterclockwise fashion such that it is oriented in between and parallel to the ribs Once the hepatorenal recess comes into view, the probe can be moved or fanned superiorly toward the patient’s head and inferiorly toward the feet to visualize Morison pouch completely, as well as the inferior portions of the liver and kidney ( Video 131.2 ) As mentioned earlier, blood will tend to accumulate in these dependent portions of the peritoneal cavity initially ( Video 131.3 ) The splenorenal recess is often more difficult to view Because the left kidney sits more superior and posterior than the right kidney, starting position for the probe is the coronal plane (marker to the patient’s head) between the fifth and seventh ribs in the posterior axillary line on the left Rotation of the probe slightly should help avoid rib shadows In this view, blood will frequently accumulate between the spleen and diaphragm, so it is important to visualize the superior