Focused assessment with sonography for trauma
Focused abdominal ultrasound for trauma, commonly abbreviated as FAST and also known as focused assessment with sonography for trauma, is a rapid, bedside, ultrasound examination performed by surgeons and emergency physicians to screen  for significant hemoperitoneum or pericardial tamponade after trauma.
The four areas that are examined for free fluid are the perihepatic (hepato-renal space), perisplenic space, pericardium, and the pelvis.  With this technique it is possible to identify the presence of free intraperitoneal or pericardial fluid, which in the context of traumatic injury, is usually due to bleeding.

# Advantages
FAST is less invasive than diagnostic peritoneal lavage and less costly than computed tomography, but achieves a similar accuracy.

# Interpretation
In hemodynamically unstable patients, a positive FAST result suggests hemoperitoneum and laparotomy should be performed in most cases. In hemodynamically unstable patients with a negative FAST result, a search for extra-abdominal sources of bleeding should be performed. In hemodynamically stable patients, a positive FAST result should be followed by a CT scan to better define the nature of the injuries.

# Technique

## Pericardial Examination
Fluid that accumulates between the visceral and parietal pericardial layers appears as a dark anechoic stripe. The subcostal view is often performed during FAST. Its obtained through placing the probe in the subxiphoid area with the pointer directed toward the patients right side and the its surface directed toward the patients left shoulder. The body of the probe lies nearly flat on the patients abdomen.
If adequate visualization cannot be obtained through this view, most often in obese patients, a transthoracic view should be obtained. Its obtained through placing the probe perpendicular to the patients chest at the fourth or fifth intercostals space (ICS) to the left of the sternum with the pointer directed towards the patients right shoulder. This view may be improved by placing the patient in the left lateral decubitus position which brings the heart closer to the chest surface.

## Abdominal Examination
The purpose is to identify free fluid in the peritoneal cavity. This fluid presumed to be blood and a sign of injury although it may represent urine in cases of pelvic trauma. Free fluid appears as an anechoic collection. The study is considered negative only if all views are free of fluid and indeterminate if any one view cannot be assessed adequately.
- Right flank  The liver provides the sonographic window. This view is obtained by placing the probe perpendicular to the abdomen with the pointer towards the patients head between the midclavicular and posterior axillary line at the tenth or eleventh ICS. Rib shadowing can be overcome by rotating the probe in a counter-clockwise direction or asking the patient to breath in and out.
- Left flank  The spleen provides the sonographic window in this view. Its obtained by again placing the probe perpendicular to the abdomen with pointer towards the patients head at or posterior to the posterior axillary line at the eighth or ninth ICS. Rib shadowing can be overcome by rotating the probe in a clockwise direction or asking the patient to breath in and out.
- Pelvic view  The bladder provides the sonographic window in this view. Its obtained through placing the probe in a sagittal orientation just above the symphysis pubis with the pointer directed to the patients head. The probe is moved across the entire bladder looking for free fluid behind the bladder in males and behind the uterus females. The probe may be rotated 90 degrees to obtain a transverse view.