my only query on this - surely any penetrating abdo trauma significant enough to get a FAST is also going to get a CT?
From Dynamed re FAST: Unlike in blunt abdominal trauma, utility of FAST for penetrating abdominal trauma is variable, because of varying sensitivities (46%-100%) and specificities (48%-100%). It is useful, however, if concerned for cardiac tamponade
Also - unstable pts should also get an ex-lap (as well as a bunch of others, but too much for STEP imo) - Tintinalli EM manual p1754.