How to read a FAST ultrasound
Other platforms explain it with text and video. In Making Synapses you practice it on the patient.
The FAST exam is a quick bedside ultrasound in trauma that looks for blood in the belly and around the heart. In an unstable patient, a positive FAST can mean going straight to surgery.
Step by step
Know the four views
Right upper quadrant, left upper quadrant, pelvis and the view under the breastbone for the heart. The extended FAST adds lung views for pneumothorax. [1]
Know what blood looks like
Free fluid appears black (anechoic) in spaces where organs normally touch. [1]
Right upper quadrant
Look between the liver and kidney, and at the tip of the liver, which often shows fluid first. [1]
Left upper quadrant
Look above the spleen first and then between the spleen and kidney. [1]
Pelvis and heart
Look behind the bladder for fluid. In the heart view, look for a black band of fluid around the heart. [1]
Watch for mimics
Fat pads, fluid-filled bowel, the gallbladder and seminal vesicles can look like free fluid. Clotted blood can look gray. [1]
Act on the result
A positive FAST in an unstable patient guides urgent surgery. A negative FAST does not rule out injury; repeat it or get a CT if the patient is stable. [2]
Common errors
- Treating a negative FAST as proof of no injury.
- Skipping the liver tip and missing early fluid.
- Calling fluid-filled bowel free blood.
FAST views [1]
| View | Where to look | Positive sign |
|---|---|---|
| Right upper quadrant | Between liver and kidney, liver tip | Black stripe of fluid |
| Left upper quadrant | Above the spleen and between spleen and kidney | Black fluid around the spleen |
| Pelvis | Behind the bladder | Black fluid pocket |
| Subxiphoid (heart) | Around the heart | Black band of fluid in the pericardium |
Practice it in Making Synapses
In Making Synapses you do this on the patient, not on paper: every step goes on the checklist with a score, and in Teach mode Blocky tells you what comes next.
Making Synapses cases that train this skill
- Post-traumatic stress disorder
- Traumatic cardiac arrest
- Fall from a ladder, multi-system trauma
- Facial trauma with airway risk
- Cardiac tamponade
- Barotrauma of the ear
15 Making Synapses cases train this skill: open the case library
Sources
Facts and steps follow AAMC Core Entrustable Professional Activities (Core EPAs); NCCPA PANCE Content Blueprint. Making Synapses is not affiliated with these organizations. Updated: 2026-10-11.