the injured patient The basic sonographic question when performing the FAST examination is “Is there free fluid in the peritoneum or pericardium?” The enhanced FAST, or eFAST, includes the additional evaluation of the pleural space for pneumothorax or hemothorax The overarching principle of the FAST examination is that hemoperitoneum or hemopericardium is an indication of organ injury in the setting of blunt or penetrating torso trauma Blood in the abdomen or thorax will appear hypoechoic or anechoic (dark) against the hyperechoic (bright) background of the internal organs (Fig 131.4 ) Thus, the detection of peritoneal or pericardial fluid by sonography may be evidence of injury to the abdominal organs or heart, respectively Although computed tomography (CT) remains the study of choice for the stable pediatric patient with suspected intra-abdominal injury, the FAST scan has several distinct advantages First, it can be performed immediately at the bedside and is interpreted by the person performing the test, who is directly aware of the clinical context Second, there is no exposure to the ionizing radiation of CT, and sedation is not needed for FAST Additionally, the FAST scan can be repeated with serial examinations if the patient’s condition changes Finally, for unstable patients, CT may not be a viable option, and the FAST scan can frequently provide valuable information that may guide therapeutic or operative interventions Research pertaining to the FAST scan has been plentiful, mainly focused in the adult population, with several pediatric studies Published data indicate that the sensitivity of FAST scan in children is not as robust as in adults but the specificity remains very high Thus, a positive FAST scan should always prompt either further investigation or therapeutic intervention A negative FAST scan does not necessarily obviate the need for CT scan but can still be valuable in patients with a low pretest probability of intra-abdominal injury