FAST and eFAST Ultrasound: Views, Findings and Limits
The FAST scan asks one question quickly: is there free fluid where there should be none? eFAST adds the chest. The views in order, what a positive and a negative scan mean, where FAST misses injuries, and what an emergency department needs from the machine.
What FAST and eFAST are
FAST — focused assessment with sonography for trauma — is a bedside scan for free fluid in the abdomen and around the heart, which in an injured patient is presumed to be blood. eFAST, the extended FAST, adds both sides of the chest for pneumothorax and blood in the chest. It uses no radiation and is done during resuscitation, not instead of it.
A yes-or-no question
FAST does not grade organ injuries. It answers whether fluid is present in each view, and the trauma team decides what to do with that answer.
Repeatable
A scan can be repeated whenever the patient changes. An early negative scan can turn positive as bleeding continues.
Not only trauma
The same views are used to look for fluid in unexplained low blood pressure, and for effusions and ascites from plasma leakage in dengue.
Dengue: scanning for plasma leakageThe views, in order
| View | Probe position | What you look for |
|---|---|---|
| Right upper quadrant (RUQ) | Right side, mid- to posterior axillary line over the lower ribs | Fluid between the liver and the right kidney (Morison’s pouch), around the tip of the liver and above the diaphragm |
| Left upper quadrant (LUQ) | Left side, further back and higher than on the right | Fluid between the spleen and the diaphragm — where it often collects first on the left — and between the spleen and the kidney |
| Pelvis | Just above the pubic bone, in transverse and longitudinal | Fluid behind the bladder, or behind the uterus in women (the pouch of Douglas); a full bladder makes this view easier |
| Pericardial (subxiphoid) | Under the breastbone, aimed towards the left shoulder; a parasternal view if that window is poor | A dark band of fluid around the heart |
| eFAST: front of the chest | Second or third rib space, mid-clavicular line, on both sides | Lung sliding at the pleural line; its absence, especially with a lung point, suggests pneumothorax |
| eFAST: lower chest | Above the diaphragm in the RUQ and LUQ views | Dark fluid above the diaphragm and loss of the normal mirror image suggest blood in the chest |
Read next Lung sliding, lung point and B-linesThe mirror image and other artefacts
Probes and presets
Curved (convex) probe
The usual probe for the abdominal and pelvic views: low frequency to see deep, with a wide field of view.
Phased-array probe
A small footprint that fits between the ribs. Good for the cardiac view and for difficult upper-quadrant windows. Many teams do the whole FAST with one probe to save time.
Linear probe
The sharpest view of the pleural line for pneumothorax. A curved or phased probe also works when time is short.
Presets
Start from a FAST or abdomen preset. For the pleural line, a lung preset — or harmonics and smoothing turned down — shows lung sliding and artefacts more faithfully.
Knobology: depth, gain and harmonicsWhat a positive and a negative scan mean
- Positive: a black (anechoic) stripe or pocket in one of the spaces where fluid collects. Fresh blood is black; clotted blood can be grey and easy to mistake for tissue.
- In a patient with low blood pressure, a positive FAST tells the trauma team the abdomen or the pericardium is a likely source of bleeding and supports acting quickly.
- Negative: no fluid seen at that moment. It does not rule out injury. Repeat the scan if the patient changes, and use CT once the patient is stable enough.
- Sensitivity depends on the operator and how much fluid there is. Studies suggest several hundred millilitres may be needed in the abdomen before the RUQ view is reliably positive, though skilled operators detect less.
- Published series report high specificity for free fluid, but ascites, dialysis fluid, recent lavage and a little normal pelvic fluid in women of reproductive age also look black.
Where FAST misses injuries
- Bleeding behind the abdominal cavity (retroperitoneal) — from the kidneys, pancreas or pelvic fractures — may show no fluid in any FAST view.
- Injuries to bowel and the diaphragm.
- Solid-organ injuries with little or no free fluid, which are more common in children.
- Obesity, air under the skin (subcutaneous emphysema) and bowel gas, which can block the views.
- A fat pad in front of the heart mistaken for a pericardial effusion, or fluid in the stomach or bowel mistaken for free fluid.
What an emergency department needs from the machine
- Fast start-up from cold or sleep, and a battery that keeps scanning when the cable is pulled.
- Curved and phased-array probes connected and selectable without swapping, plus a linear probe for the chest and vascular access.
- A FAST or eFAST preset and worksheet that records each view as positive, negative or indeterminate.
- Clip storage: a short loop shows fluid and lung sliding far better than a still image.
- A compact cart that fits beside a resuscitation bed, and surfaces that can be wiped down after blood contamination.
- DICOM export to PACS or the emergency record, so the scan becomes part of the notes.
Read next POCUS equipment for emergency and ICUHandheld options for FASTDICOM, PACS and image storage
Training and documentation
FAST is a core application in emergency medicine ultrasound training. Record every view, save the clips, and log each scan against the final outcome — CT, surgery or follow-up — so each operator can see how accurate their scans are.
Related guides
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Frequently asked questions
What does FAST stand for in ultrasound?
Which probe is used for a FAST scan?
Does a negative FAST rule out internal bleeding?
How long does a FAST scan take?
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