Boring Em - Posted by Michael Butler
"The FAST exam is a useful diagnostic test for adult trauma patients that present with possible abdominal injury. The Canadian Association of Emergency Physicians (CAEP) has endorsed FAST as a point-of-care ultrasound modality in the emergency departments [1]. Advanced Trauma Life Support (ATLS) guidelines consider it an adjunct to the primary survey [2]. In the context of abdominal trauma, the primary use of the FAST exam is the detection of . We can use it to detect as little as 200 mL of fluid in the abdomen[3].
There has been some debate amongst trauma specialists about the utility of the FAST exam [4,5,10]. In particular regarding its sensitivity and specificity, and whether it reduces the incidence of unnecessary imaging, such as computed tomography (CT), or invasive interventions, such as diagnostic peritoneal lavage (DPL) and exploratory laparotomy [4].
The usefulness of the FAST exam is in primarily in ruling in intra-abdominal injury; its specificity in the hands of emergency physicians in this setting has been proven [4,9]. If the emergency physician detects fluid, the specificity of the FAST exam for this finding is high, between 96.0 and 100.0% [4-10]. A negative sonogram does not, however, definitively rule out an intra-abdominal injury; the reported sensitivity of the FAST exam is between 42.0% and 96.0% [4-10]. These numbers are a moving target, since the sensitivity and specificity of the FAST exam depends on a number of other factors, including operator experience, time since injury, and volume of pathological intra-peritoneal fluid.
In the setting of acute trauma, these characteristics support its use as a screening test to decide on further management. If the patient is hemodynamically-stable and the FAST exam is positive, they usually will require a CT scan to further characterize their injuries. If the FAST exam is negative, CT may be clinically indicated to definitively rule out intra-abdominal injury.
If the patient is hypotensive, a positive FAST exam strongly indicates the need for therapeutic laparotomy. A negative FAST exam does not preclude hemoperitoneum, so one may need to employ alternate clinical tools in order to search for other sources of hypotension.
The Bottom Line
The FAST exam is highly-specific for intra-abdominal injury, and useful in the hemodynamically-unstable patient. An algorithm summarizing these findings is shown in Figure 1.
http://boringem.org/2015/12/14/boring-question-what-is-the-role-of-the-fast-exam-for-blunt-abdominal-trauma/