Focused Assessment with Sonography for Trauma (FAST) scan
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At the time the article was created Ian Bickle had no recorded disclosures.View Ian Bickle's current disclosures
At the time the article was last revised Henry Knipe had the following disclosures:
- Integral Diagnostics, Shareholder (ongoing)
- Micro-X Ltd, Shareholder (ongoing)
These were assessed during peer review and were determined to not be relevant to the changes that were made.View Henry Knipe's current disclosures
It is invariably performed by a clinician, who should be formally trained, and is considered as an 'extension' of the trauma clinical assessment process, to aid rapid decision making. Some studies have shown no significant difference in diagnostic accuracy between radiologists and non-radiologists 6.
The chief aim of the study, in a trauma patient, is to identify intraperitoneal free fluid (assumed to be hemoperitoneum in the context of trauma) allowing for an immediate transfer to operating theater, CT or other. Solid organ injury is seldom identified, and when present may warrant further investigation.
Many papers have been published detailing the pros and cons of this investigation 1,2. FAST scanning has a reported sensitivity of ~90% (range 75-100%) and a specificity of ~95% (range 88-100%) for detecting intraperitoneal free fluid 4. Sensitivity for detecting solid organ injuries is much lower.
Most studies in the emergency medicine literature dictate that peritoneal free fluid will not be identified by ultrasonography until more than 500 mL is present. Therefore, a negative exam will not preclude a bleed which will eventually become significant. Moreover, mesenteric vascular injuries, solid organ injuries, hollow viscus injuries, and diaphragmatic injuries may not result in free intraperitoneal fluid, and thus may not be detected 10.
It has replaced diagnostic peritoneal lavage as the preferred initial method for assessment of hemoperitoneum.
In several recent studies, the sensitivity and specificity of thoracic ultrasonography use for the detection of pneumothorax after blunt injury was 86-98% and 97-100%, respectively, outperforming the supine chest x-ray 12.
patient in supine position
3.5-5.0 MHz convex transducer
five regions may be scanned 3,10:
pericardial view: commonly referred to as the subcostal or subxiphoid view
to examine the pericardium, the liver in the epigastric region is most commonly used as a sonographic window to the heart
the potential space between the visceral and parietal pericardium is examined for a pericardial effusion
if anatomical factors preclude epigastric probe placement, parasternal or apical four-chamber views may be used
right flank view
commonly referred to as the perihepatic view, Morison pouch view or right upper quadrant view
four potential spaces are sequentially examined for the accumulation of free fluid
the hepatorenal interface (Morison pouch) is first identified, with subsequent assessment of the more cephalad subphrenic and pleural spaces
visualization of the inferior pole of the kidney, which is a continuation of the right paracolic gutter, defines the caudad extent of an adequate view
left flank view
commonly referred to as the perisplenic or left upper quadrant view
four potential spaces are sequentially examined in an analogous fashion to the right flank, albeit the splenorenal interface is assessed on the left
An extended FAST or "eFAST" scan is now standard of care, and is performed by incorporating two views assessing the anterior thorax 7:
anterior pleural views
the probe is placed in a sagittal orientation in the midclavicular line between the clavicle and diaphragm
anterior and lateral interrogation of interspaces 5-8 bilaterally is recommended 9
Causes of false negatives
obesity: severely limits assessment of the peritoneal cavity
posterior acoustic enhancement caused by the fluid-filled bladder can result in free fluid being missed in the pelvic view
Causes of false positives
seminal vesicles mistaken for pelvic free fluid in the young male patient
History and etymology
Ultrasound was first used for the examination of trauma patients in Europe in the 1970s 8.