Introduction
The FAST exam is a non-invasive study used to evaluate the peritoneal, pericardial and/or pleural spaces for the presence of pathologic free fluid. This fluid may consist of blood, bowel contents, urine, or a combination thereof. In the case of the pleural space, the pathology usually represents the presence of blood or air. This exam incorporates multiple sonographic views of various anatomical structures that are easily accessible to the average emergency physician during a typical trauma evaluation. The FAST may be deployed rapidly during the evaluation of a patient, and most often is indicated during the late primary, or secondary survey. Since the exam focuses on specific area of the patient, it may occur before, after or in conjunction with additional studies. Because of the non-specific nature of the FAST, it should always be interpreted along with other clinical, historical and laboratory data. A great advantage of the FAST is that it may yield a wealth of information without having to remove the patient from the resuscitation area. To provide the most accurate status of the patient, the FAST should be repeated as frequently as clinically indicated, as fluid may have not accumulated to a detectable extent at the time of the initial study.
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Dr. Thomas Cook performing a FAST exam
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Indications
1. Primary
a. To rapidly assess the torso for pathologic free fluid suggestive of injury in the peritoneal, pleural or pericardial cavities
2. Extended
a. Pneumothorax/Hemothorax
b. Solid organ injury (i.e., liver, spleen)
c. Hollow organ rupture (i.e., bladder, viscus)
d. Triage of multiple or mass casualties
Contraindications
There are no absolute contraindications to FAST. However, the clinical status of the patient and the extent of injuries should guide the physician to determine the value of this exam.
Limitations
The FAST exam, like other sonographic studies, is not always the most accurate means of evaluating a suspected or potential injury. It is a focused examination of specific regions of the body and should not be expected to evaluate all abnormalities resulting from truncal trauma. Therefore the physician should interpret the FAST data in the context of the entire clinical picture. While it may yield useful information, the FAST should not delay more advanced imaging studies or obviously necessary surgery.
The FAST also has physical limitations. An obese patient may be more difficult to scan effectively simply due to the physical properties of the sonographic technology. In addition, the presence of air between the ultrasound probe and the area of study (i.e., bowel gas, subcutaneous emphysema) will diminish or obstruct the image. Again, this is due to the physical properties of the technology.
Caution should be taken in using data collected from the FAST in specific patient populations. Patients with certain comorbid conditions such as ascites or renal disease requiring dialysis may yield false positive exams due to preexisting free fluid collections.
Special Thanks to Chad Bevan MS-IV for scripting this primer!
Onto Pitfalls of the FAST Exam
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