SonoTips&Tricks: The FAST scan: Suprapubic View #FOAMus #FOAMed

By Viveta Lobo, MD and Laleh Gharahbaghian, MD, FACEP

Our latest insert in the ACEP Ultrasound Section newsletter is below – on the FAST scan – the Suprapubic sections. The prior entries was on the FAST scan: The Cardiac views ( go here) and The Upper Quadrants ( go here. ). The ACEP US Section is the go-to site for everything you want to know about starting an US program, credentialing in ultrasound, the policies and politics, and is the home of SonoGuide – an amazing educational resource for bedside ultrasound, and the EMSONO: Ultrasound Test. It is also where we add our entries for their newsletter that goes over tips and tricks, cases, and all things ultrasound in the news. We recently wrote an article for the ACEP Ultrasound Section Newsletter – which is available for all members of the ACEP US Section – and I highly recommend becoming a member – it’s totally worth it.”

It was a TRUE pleasure to record a podcast recently with Dr. Scott Weingart (aka, my hero) on EMCrit (twitter: EMCrit), and writing this article with our newest ultrasound faculty member, Dr. Viveta Lobo, describes some of what was spoken about.

As discussed in our last entry, the FAST exam is undoubtedly the most widely used bedside ultrasound application used in emergency medicine. Its incorporation in the ATLS revised protocol, the RUSH exam, and several other published protocols, makes it an invaluable screening tool for intra abdominal injury causing hemoperitoneum, cardiac injury with pericardial effusion, and unexplained hypotension.(1,2)

We will continue our discussion of the FAST scan by reviewing the pelvis views, and relay some tips and tricks. Refer to the March 2013 Newsletter for our article reviewing tips for scanning the right upper quadrant (RUQ) and left upper quadrants (LUQ), and the June 2013 newsletter for our article reviewing the tips for the cardiac views.

The Suprapubic View
The suprapubic view on the FAST exam is generally the last of the four views performed.

Theoretically, given its dependent anatomical position, one might logically conclude that it should in fact be the most sensitive view to visualize free fluid; unfortunately, the literature has negated this theory – and in fact this can often be the least sensitive view, largely in part of human error, and especially in pelvic fractures.(1,2,4) Anatomically, when we scan the suprapubic area in both transverse and longitudinal planes, there’s a lot that we see –the bladder, bowel, pelvic bones, pelvic organs, and rectum to name a few. This might make it harder for us to visualize free fluid, and separate it out from these other structures. But here’s a few tips to help overcome these limitations. Begin by placing your phased array or curvilinear probe just above the pubic symphysis, aiming inferiorly/caudad into the pelvis.

 

 

 

 

 

 

 

Tips for the Suprapubic View: 

 

 

 

 

 

 

 

1. Look through a full bladder. A full bladder – The suprapubic view is visualized using a filled bladder as the acoustic window. Not all trauma patients come in with a full bladder and we will not likely go back to the days when a foley catheter used to be placed in order to fill the bladder for visualization. While we are sure our patients appreciate us not doing this anymore – its important to note, that if your patient has an empty bladder, it is best to hydrate them up with the fluids, and repeat the scan when the bladder is more full.(5) With an empty bladder your ability to adequately discern free fluid is very limited. Mostly due to gas scatter from bowel, inadequate depth adjustments, and inability to discern bowel fluid from free fluid. Click Here for a Video of A Normal Female.

2. Adjust your depth – More often than not, when it is time to scan the suprapubic area, your depth is set too deep from scanning the upper quadrants or cardiac views. We often find that a depth of about 13cm to 16cm optimizes your view. The goal is to have your bladder centered on the screen, to easily visualize the areas surrounding the bladder

 

 

 

 

 

 

3. Adjust your gain – The bladder is a fluid filled structure, and as mentioned before, fluid is the “lover” of ultrasound, allowing structures deep to it to be well visualized, however this often creates an artifact called “posterior acoustic enhancement” that produces a hyperechoic and bright area deep to the bladder. This makes it hard to visualize anechoic or black free fluid. One of the biggest pitfalls is not decreasing your gain to accommodate for this, and limiting your ability to pick up anechoic free fluid.
A good rule of thumb, is to ensure that you can easily visualize pelvic organs. If you are able to identify a uterus or a prostate easily, that usually means you have adjusted your gain appropriately. Click Here for a Video of Posterior Acoustic Enhancement.

 

 

 

 

 

 

 

 

4. Look everywhere – Unlike in your upper quadrants, free fluid in the pelvic cavity can in fact collect anywhere – anterior, lateral, and posterior to the bladder as well as anterior, lateral, and posterior to the uterus in female patients. This often is dictated by your patient’s position, the lay of the uterus, how full the bladder is, and the size of the prostate to name a few. We suggest looking in four areas –

a. Look anterior and cephalad to the bladder. Click Here for Video of Free Fluid Anterior to the Bladder. This is especially true if the bladder is empty. At times, free fluid will be mistaken for the bladder and thought to be a septated bladder, when in fact it is free fluid cephalad to the bladder. Click Here for Video of Free Fluid Easily Mistaken for Bladder.

b. Look adjacent/lateral to your bladder; free fluid will collect into a “wedge” shape or triangular shape in between bowel folds which will be most evident with appropriate fanning through the region. Click Here for Video of Wedge of Free Fluid.

c. Look deep/posterior to the bladder between it and your pelvic organs. Click Here for Free Fluid Posterior to the Bladder. Especially in females, you can see a collection of free fluid between the bladder and the uterus. This often looks like boxed shaped anechoic structures that as you fan through will appreciate it not being a “contained” structure.

d. Look posterior to your pelvic organs. Free fluid can collect deep to your uterus or prostate. Click Here for Video of Free Fluid Posterior to the Uterus.

 

 

 

 

 

 

 

 

 

5. Seminal vesicles are also anechoic/black – In males, don’t be fooled by the seminal vesicles. These lie immediately posterior to the bladder, and often appear like a anechoic “bow-tie” shape, with contained fluid and equal on each side.
They will always appear in the same location, and you should fan slowly and carefully through the region to ensure that this is a contained structure and not mistake it for free fluid.

 

 

6. Physiological free fluid in females – In menstruating females you can appreciate some physiological free fluid that may be normal. This is hard to differentiate truly from traumatic free fluid, and you will need to consider the clinical picture – Is there any abdominal pain? Is there abdominal or pelvic trauma? Are her vital signs abnormal? Also, the amount and location of free fluid can help – physiological free fluid is found deep to the uterus, and along its border – it should not be greater than 1/3 the length of the border, anything greater than 1/3 should be considered pathological.

 

 

 

 

 

 

 

7. Fan slowly – While fanning is always important in evaluating any region by ultrasound – we cannot stress it enough when evaluating the suprapubic area. It is impressive and often surprising just how much free fluid can “hide” behind and around the many structures present in this region, and not be visualized unless you dedicatedly fan through the area. It is strongly encouraged to view the suprapubic area in 2 planes – horizontally and longitudinally and fan through each section slowly to make sure you don’t miss any free fluid!(3)

8. Quick Pregnancy Test– In female patients of reproductive age, while performing the pelvic view, take a quick look inside the uterus. You just may quickly get your answer to whether she is pregnant or not but visualizing a gestational sac with fetal pole or yolks sac. However, if you only see a gestational sac and you are performing a FAST scan for unexplained hypotension or shock, this could be an identifier for a pseudosac of an ectopic pregnancy.

 

 

 

 

 

 

 

 

Look out for the next and last entry on the FAST scan – the Lung Views in the next newsletter.

References

1. Abrams BJ, Sukumvanich P, Seibel R, et al. Ultrasound for the detection of intraperitoneal fluid: the role of Trendelenburg positioning. Am J Emerg Med. 1999;17(2):117-20.
2. Friese RS, Malekzadeh S, Shafi S, et al. Abdominal ultrasound is an unreliable modality for the detection of hemoperitoneum in patients with pelvic fracture. J Trauma. 2007;63(1):97-102.
3. Ma OJ, Kefer MP, Mateer JR, et al. Evaluation of hemoperitoneum using a single- vs multiple-view ultrasonographic examination. Acad Emerg Med. 1995;2(7):581-6.
4. Von Kuenssberg Jehle D, Stiller G, Wagner D. Sensitivity in detecting free intraperitoneal fluid with the pelvic view of the FAST exam. Am J Emerg Med. 2003;21:476-8.
5. Blackbourne LH, Soffer D, McKenney M, et al. Secondary ultrasound examination increases the sensitivity of the FAST exam in blunt trauma. J Trauma. 2004;57:934-8.