Recognizing free fluid on FAST

Step-by-step approach

1. 1

   The question FAST answers

   Is there free fluid (blood) in the peritoneal, pericardial, or pleural spaces of an unstable trauma patient? It is a decision tool, not a survey.

2. 2

   RUQ — Morison's pouch

   The hepatorenal recess is the most dependent supine recess and the highest-yield single view. Free fluid = anechoic stripe between liver and kidney. Sweep the whole recess and the caudal liver tip.

3. 3

   LUQ

   Fluid collects above the spleen (subphrenic) before the splenorenal recess — go a rib space higher and more posterior than you think.

4. 4

   Pelvis

   The rectovesical or rectouterine pouch is the most dependent space overall; a full bladder is your acoustic window.

5. 5

   Pericardial

   Subxiphoid view for pericardial fluid — see the pericardial effusion guide topics for tamponade signs.

6. 6

   Decision rule

   Unstable + positive FAST → theatre. Stable → CT. Negative FAST does NOT exclude injury: it rules in, not out.