The Most Sensitive View of the FAST

Caudal edge byte


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

Western Journal of Emergency Medicine February 2017 - Pubmed Link



Take Home Points

1. The right upper quadrant was the most commonly positive view, and the caudal tip of the liver was the most commonly positive sub-quadrant for free intraperitoneal fluid.

2. Splenodiaphragmatic space was the most commonly positive in the LUQ.

3. Lateral to bladder and posterior to uterus were the most commonly positive in the pelvic views.


Background

The FAST (focused assessment with sonography in trauma) is a combo of ultrasound views designed to look for free fluid in the abdomen and around the heart in a trauma patient. Traditional teaching (confirmed in prior studies) is that intraperitoneal free fluid goes first to the right upper quadrant (RUQ) and pelvis in the supine trauma patient. However, there is multiple spaces for the fluid to collect within each of the three abdominal views. It can be helpful to know which areas of the abdomen are most commonly positive when there is intraabdominal free fluid (in trauma, presumed to be blood from an injury). To date, there has not been much study regarding which part of the views are the most sensitive.


Question

What areas of the right upper quadrant (RUQ), left upper quadrant (LUQ), and suprapubic (also known as pelvic) areas most commonly have free fluid in a positive (abdominal) FAST exam?


Population

Single trauma center, ultrasounds performed between 1/2012 to 6/2013

Inclusion

  • Adult trauma patients

  • Supine

  • Must have had COMPLETE (included all regions) intraperitoneal views of SUFFICIENT quality


Exclusion

  • Unable to confidently assess all regions for free fluid

  • All three views not performed or recorded

  • Poor image quality that could not be assessed

  • Medical information unavailable (could not perform chart review to assess true positive or false positive)


Who did the scans?

Emergency medicine residents of all levels of training


Design

Retrospective analysis

One fellowship trained EM faculty and 3 senior EM residents reviewed all the FAST exams

Positive defined as any free fluid within the peritoneum seen on ultrasound.

Compared with CT performed directly after ultrasound or an operative report.


**The Sub-quadrants"

Right upper Quadrant

RUQ1 - hepato-diaphragmatic space (area between diaphragm and liver)

RUQ2 - hepato-renal space, or Morison’s pouch (area between liver and kidney)

RUQ3 – caudal edge of the liver, superior right paracolic gutter area


Left Upper Quadrant

LUQ1 - spleno-diaphragmatic space (area between spleen and diaphragm)

LUQ2 - spleno-renal space (area between spleen and kidney)

LUQ3 - inferior pole of the left kidney or left paracolic gutter


Suprapubic

SP1 - lateral on either or both sides of bladder

SP2 - posterior to bladder and anterior to pelvic organs

SP3 - posterior to uterus also known as the pelvic cul-de-sac (obviously this view can only be found in females)


Intervention

All patients received a FAST exam

Patients with +free fluid then either received CT imaging or went straight to operating room - based on discretion of treating physicians at that time.

Reviewers looked at these exams retrospectively and determined if there was free fluid present.

Then chart review performed to determine if the cases with free fluid had confirmed intraperitoneal fluid either on CT or based on operative report.


The Scan

FAST exam

Curvilinear or Phased Array probe

probe


Learn how to do a FAST exam in 5 minutes! - 5 minute sono


Results

FAST Images

1158 reviewed → 105 excluded due to incomplete, poor quality, incorrect medical record information → 1008 analyzed → 48 (4.8%) positive → 39 had CT, 9 went to OR


Primary Outcome

RUQ was most commonly positive. Caudal tip of the liver was most commonly positive within the right upper quadrant. Note - multiple quadrants were positive in the same exam (hence totals add up to >100%).

RUQ table

*No statistical significance in difference between RUQ2 and RUQ3


Splenorenal was most commonly positive in LUQ - the tried and true teaching was confirmed in this study. LUQ table


In the suprapubic/pelvic views lateral to the bladder was most commonly positive overall, but in females, posterior to the uterus was the most common. Suprapubic table


Other Findings

No false positive exams.

RUQ3 (caudal tip of liver) was always positive when RUQ2 (Morison’s pouch) was positive.

Two cases of isolated hepatodiaphragmatic free fluid on FAST - likely due to poor visualization of other areas, free fluid in all RUQ areas confirmed on CT

5 cases where LUQ positive but RUQ negative - check out our post and podcast on this study about isolated LUQ fluid in the FAST


Limitations

Does most commonly positive mean most sensitive? Sensitivity means true positives divided by (true positives + false negatives). We don’t know the false negatives in this case. However, maybe the reasoning is that if it is most commonly positive, it is least likely to be falsely negative and therefore could be said to be the most sensitive? Maybe just semantics? Hmmmm.

Some scans not recorded

Amount of time between trauma and FAST and FAST and CT/OR was not recorded

No inter-rater reliability

What did we miss by excluding poor quality or incomplete images? It was about 9% of their exams in this case. Maybe the incomplete exams were incomplete because they saw free fluid in Morison’s pouch and therefore did not feel the need to view caudal liver? That would change up the numbers a bit, although unlikely to change the overall point.

Does it change practice? Maybe it will change your teaching. This is important information, but you should still get all the views - now you just know where it may be most likely to be.


Take Home Points

1. The right upper quadrant was the most commonly positive view, and the caudal tip of the liver was the most commonly positive sub-quadrant for free intraperitoneal fluid.

2. Splenodiaphragmatic space was the most commonly positive in the LUQ.

3. Lateral to bladder and posterior to uterus were the most commonly positive in the pelvic views.


Our score

3 Probes


Cite this article as

Michael Prats, MD. The Most Sensitive View of the FAST. Ultrasound G.E.L. Podcast Blog. Published on March 27, 2017. Accessed on July 16, 2019. Available at https://www.ultrasoundgel.org/16.
Published on 03/27/17 02:00 AM
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