Step 1: This is penetrating trauma to the right LOWER chest, an area that straddles the chest and the upper abdomen, so both cavities are at risk. He responded to fluids and is now haemodynamically stable.
Step 2: The chest X-ray is clear, which argues against a large haemo/pneumothorax, so a blind chest tube is not the immediate next step.
Step 3: The fastest bedside tool to screen for free fluid (blood) in the pericardium, pleural spaces, and peritoneum is the extended FAST (eFAST). It is quick, repeatable, and needs no transport, making it the logical next step right after resuscitation.
Why not CT: CECT (chest or abdomen) is more sensitive in a stable patient, but eFAST comes first as the immediate screening step; CT follows if eFAST is positive or equivocal. A chest tube is not indicated with clear lung fields and no signs of tension.
Ref: Bailey and Love, Short Practice of Surgery, 27th edition, Pg 366, 372.