The FAST and eFAST exam in trauma

What it is

Focused Assessment with Sonography for Trauma (FAST) is a bedside ultrasound done during the primary survey to look for free fluid, which in trauma is presumed to be blood. It has four views: the right upper quadrant (hepatorenal space, Morison's pouch), the left upper quadrant (splenorenal and subphrenic spaces), the pelvis (behind the bladder) and the subxiphoid view of the pericardium. The extended FAST (eFAST) adds both anterior chests to look for pneumothorax and the spaces above each diaphragm for haemothorax. It takes a few minutes, can be repeated as often as needed and uses no radiation. A positive scan in an unstable patient changes management at once; a negative scan does not exclude injury.

What to check

• Free fluid is anechoic (black) and collects in the dependent spaces; clotted blood can be grey and is easy to miss.
• The right upper quadrant is the most sensitive view, and the lower tip of the liver is where fluid shows first.
• In the left upper quadrant, blood often gathers above the spleen, under the diaphragm, before it reaches the kidney.
• In the pelvis, look behind the bladder: rectovesical pouch in men, rectouterine pouch (of Douglas) in women.
• FAST misses retroperitoneal bleeding, hollow-viscus and diaphragm injuries, and solid-organ injuries without free blood.

Reading it step by step (and why)

1. Use a curvilinear (or phased-array) probe with the patient supine — the views are dependent spaces where blood pools.
2. Pericardium first, subxiphoid, probe aimed at the left shoulder — a black stripe around the heart suggests haemopericardium.
3. Right upper quadrant, mid-axillary line, lower ribs — look between liver and kidney and at the liver tip, where fluid shows first.
4. Left upper quadrant, posterior axillary line, higher than the right — check above the spleen and the splenorenal space.
5. Pelvis, just above the pubis, transverse and sagittal — fluid lies behind the bladder; scan before a catheter empties it.
6. eFAST: both anterior chests, linear probe — lung sliding or B-lines rule out pneumothorax under the probe.
7. eFAST: look above each diaphragm — black fluid there, with the spine visible above it, means haemothorax.
8. Repeat the scan when the patient's condition changes — bleeding builds up and an early scan can be falsely negative.

Common mistakes

• Treating a negative FAST as «no injury»: it does not exclude bowel, pancreas, diaphragm or retroperitoneal injury.
• Missing clotted blood, which can be grey and look like tissue.
• Mistaking fluid-filled bowel, the stomach, a perinephric fat pad or the pericardial fat pad for free blood.
• Not tilting the probe through the whole space, so a thin rim of fluid at the liver tip is missed.
• Free fluid may be ascites, dialysate or a small physiological amount in the pelvis of a woman; read it with the clinical context.
• Delaying treatment of an unstable patient to complete a perfect scan.

Next step

• Unstable patient with a positive abdominal FAST: call the trauma surgeon for the operating room, not the CT scanner.
• Unstable patient with a negative FAST: look for other sources (chest, pelvis, long bones, outside bleeding) and repeat the scan.
• Stable patient, positive or negative FAST: CT of the abdomen and pelvis with intravenous contrast to grade the injury.
• Fluid in the pericardium with shock: call the surgeon at once for pericardial decompression.
• Pneumothorax or haemothorax on eFAST: treat according to the patient's stability, with a chest drain if indicated.

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Elsewhere in DurgiPedia

• Shock: the clinical signs and the types
• Cardiac tamponade: Beck triad and pulsus paradoxus

Connections

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Educational content; it does not replace a radiologist's report and is not a clinical instruction. Each study is ordered on the patient's assessment and your institution's protocols.

Sources: Focused Assessment With Sonography for Trauma (StatPearls (NCBI Bookshelf), 2023); Blunt Abdominal Trauma (StatPearls (NCBI Bookshelf), 2023).

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