Dr. Huang and Dr. Boukhman astutely picked up this very subtle positive FAST! Kudos! The most useful situation that decides the next best intervention is a FAST scan on an unstable blunt trauma patient. The patient's CT revealed Grade 2 and 3 liver lacerations and a small amount of hemoperitoneum without active extravasation. He was monitored in the SICU and eventually did well. This is a fantastic pick up...there is a subtle free fluid stripe in Morrison's pouch and a very small echogenic area at the inferior pole of the kidney at the lower tip of the liver. This can easily be missed. The most sensitive view of the FAST for free fluid is the RUQ, visualizing above and below the diaphragm and fanning through the ENTIRE Morrison's pouch (superior and inferior poles of the kidney). The right lobe of the liver and the inferior pole of the kidney are the most dependent positions of the RUQ where free fluid will first accumulate in most patients. Unlike the LUQ where blood is more likely to pool in the subphrenic space, the liver and the diaphragm are well opposed and protect one another from injury. By various studies, the FAST can pick up 300-500 cc of free fluid, which depends largely on maximizing image acquisition. The ability to detect lower volumes of hemoperitoneum depends on the amount of time since injury, having the PATIENT SUPINE, low levels of ambient light in the room, and of course on the operator. We can optimize our sensitivity by making sure to take the time to SLOWLY fan through the entirety of the kidney, adjusting your gain and depth to ensure the area of interest is centered on the screen avoiding wasting screen space . You will need to evaluate multiple rib spaces in the RUQ and LUQ views in order to perform a good FAST scan. Obtaining this important view that Dr Huang and Boukhman did, you can slide the probe down a rib space towards the patient's feet. If rib shadows are getting in your way, you can rotate the probe very slightly for an intercostal oblique view that may allow a better view of the kidney, liver or spleen. Finally, if the patient is stable, you can also use trendelenburg to even further increase your sensitivity of detecting free fluid in the RUQ and LUQ. The FAST has lower sensitivity with solid organ injuries, hollow viscus injuries, any injury that does not cause free fluid to develop, and does NOT detect retroperitoneal bleeding (which commonly occurs with pelvic fractures).