[Ann Emerg Med.] False-negative FAST examination: associations with patient outcomes

Image: CC/ Positive FAST – fluid (black stripe, arrows) in Morison's pouch.

Primer: The Focused Assessment with Sonography in Trauma (FAST) exam is a critical component of the initial evaluation of a patient with blunt abdominal injuries. While it is well known that the sensitivity of the FAST exam is too low to reliably rule out an intra-abdominal injury, it is not clear what significance a false negative (defined as: the existence of pathological intra-abdominal free fluid despite a negative FAST exam) bears for patient outcomes.

This [retrospective] study: Authors from the Denver Health Medical Center set out to conduct a retrospective cohort study to answer two questions: 1) What patient characteristics are most commonly associated with a false negative FAST exam and 2) are false negative FAST exams associated with any negative outcomes?

The authors analyzed demographic, injury, and outcomes data for 332 patients with pathological intra-abdominal fluid and found that 49% had a false negative FAST exam. Analysis revealed that while severe head injury was positively associated with a false negative FAST (odds ratio [OR] 4.9; 95% confidence interval [CI] 1.5 to 15.7), severe abdominal injury was negatively associated (OR 0.3; 95% CI 0.1 to 0.5).  ED vital signs, GCS score, hematocrit and fractures to specific sites (e.g. ribs, pelvis, and spine) were not associated with a false negative FAST.

Importantly, while a negative FAST exam was associated with decreased likelihood of therapeutic laprotomy, it was not linked with any increase in length of hospital stay, length of ICU stay, or mortality.  These findings were true even after controlling for age, sex, and Injury Severity Score.

In sum: While a FAST exam may be more likely to miss certain injury patterns (i.e. head injuries), overlooking these intra-abdominal free fluid collections does not seem to be associated with any major adverse outcomes for the patient. The authors suggest further studies to “clarify the strength of [their] findings and help direct changes in management.”

Click to read the study published in Annals of Emergency Medicine

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