Most ultrasound imaging is performed in B-mode (brightness), which is the standard, two-dimensional representation of the reflected ultrasound waves As described above, each pixel represents the intensity and distance (determined by time) of a returning sound wave M-mode (motion) essentially creates a single line of a sound wave through an object of interest, and then displays that image with respect to time (on the horizontal access) M-mode is useful to document movement of a structure, such as cardiac valves or the fetal heart Finally, D-mode (Doppler) and Color Flow Doppler sense the movement of the ultrasound waves as they encounter a moving medium, represented by either color changes or sound from the ultrasound machine Color Flow Doppler ultrasound is especially useful when identifying vessels and discerning between arterial and venous flow The colors represent flow away from or toward the probe and not correlate with arterial or venous flow ( Video 131.1 ) FIGURE 131.3 Image of femoral anatomy Note the marker on the screen (arrow ) is a green dot By convention, the marker should always be on the left, upper side of the monitor DIAGNOSTIC APPLICATIONS Focused Assessment With Sonography in Trauma The use of sonography in trauma was one of the very first applications of emergency POCUS, and many now consider it a standard part of the evaluation of 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 FIGURE 131.4 A positive FAST examination Note the anechoic stripe of fluid (arrows ) in Morison pouch, between the liver and kidney Anatomy When supine, there are several dependent areas of the peritoneal cavity where blood or fluid has a tendency to accumulate (Fig 131.5 ) The hepatorenal recess, also known as Morison pouch, is the potential space located between the liver and right kidney The splenorenal recess is the space located between the spleen and left kidney and no fluid should be seen here in the healthy person The rectovesical pouch (male patients) and the pouch of Douglas (female patients) are formed by the space between the rectum and bladder or uterus, respectively These potential spaces form the basis of the FAST abdominal views FIGURE 131.5 A: CT cross section of abdominal anatomy Note the dependent areas of Morison pouch (MP) and the splenorenal recess (SR) B: Pelvic anatomy Note the dependent rectovesical pouch (RP) between the posterior wall of the bladder and stool-filled rectum ... 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... 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