Caudal Edge of the Liver in the Right Upper Quadrant (RUQ) View Is the Most Sensitive Area for Free Fluid on the FAST Exam.

INTRODUCTION: The focused assessment with sonography in trauma (FAST) exam is a critical diagnostic test for intraperitoneal free fluid (FF). Current teaching is that fluid accumulates first in Morison's pouch. The goal of this study was to evaluate the "sub-quadrants" of traditional FAST views to determine the most sensitive areas for FF accumulation.

METHODS: We analyzed a retrospective cohort of all adult trauma patients who had a recorded FAST exam by emergency physicians at a Level I trauma center from January 2012 - June 2013. Ultrasound fellowship-trained faculty with three emergency medicine residents reviewed all FAST exams. We excluded studies if they were incomplete, of poor image quality, or with incorrect medical record information. Positive studies were assessed for FF localization, comparing the traditional abdominal views and on a sub-quadrant basis: right upper quadrant (RUQ)1 - hepato-diaphragmatic; RUQ2 - Morison's pouch; RUQ3 - caudal liver edge and superior paracolic gutter; left upper quadrant (LUQ)1 - splenic-diaphragmatic; LUQ2 - spleno-renal; LUQ3 - around inferior pole of kidney; suprapubic area (SP)1 - bilateral to bladder; SP2 - posterior to bladder; SP3 - posterior to uterus (females). FAST results were confirmed by chart review of computed tomography results or operative findings.

RESULTS: Of the included 1,008 scans, 48 (4.8%) were positive. The RUQ was the most positive view with 32/48 (66.7%) positive. In the RUQ sub-quadrant analysis, the most positive view was the RUQ3 with 30/32 (93.8%) positive.

CONCLUSION: The RUQ is most sensitive for FF assessment, with the superior paracolic gutter area around the caudal liver edge (RUQ3) being the most positive sub-quadrant within the RUQ.