A Few Abstracts from WCUME 2017

Podcast

WCUME byte


Abstracts from the World Congress on Ultrasound in Medical Education 2017

October 12-15, 2017. Montreal, Canada. WCUME '17 website

One point method, a rapid alternate way of DVT assessment - Abstract on WCUME Website

Prediction of fluid responsiveness following cardiac surgery using Doppler renal resistive index - Abstract on WCUME Website

Suspected small bowel obstruction in the emergency department accuracy of point-of-care ultrasound - Abstract on WCUME Website


Take Home Points

1. Don't change your practice based on abstracts.

2. One point DVT scan including phasicity - although it seems like this would miss significant proximal DVTs, none were missed in this small study.

3. Change in renal resistive index may correlate with fluid responsiveness, but differences are so small reproducibility seems a challenge.

4. A transition point may be highly specific for small bowel obstruction on POCUS.


What's going on?! Why is this episode so different?

Good question sir or madame. This episode came from the idea that there is a lot of interesting research and ideas that are presented in abstract form at conferences. It may take months or years for this research to make it into the journals and that is a little sad for the people who can't make it to that conference. Recently, Jacob and Mike were in Montreal at the World Congress on Ultrasound in Medical Education and it was phenomenal! A whole conference dedicated to the teaching of ultrasound! We thought that it might be fun to share some of the latest ideas floating around at this gathering of so many smart people in the field. NOW, before you start stomping your foot and wringing your hands in frustration - we know. Abstracts are not the same as published research. For one, they are not as rigorously peer-reviewed and may have lower standards for acceptance. Secondly, they don't give you all of the information, the character limits are too short for that. We don't know the specifics of how everything was done so we are forced to infer or assume the study was done in an appropriate way. So with that being said...

DON'T CHANGE YOUR PRACTICE BASED ON ABSTRACTS

With that in mind, we thought that it might be interesting to share some of the latest ideas cropping up in the research. As always, read responsibly. Comment at the bottom of the post if you do or don't like this idea.


1. One point method, a rapid alternate way of DVT assessment


Background

Some initial studies on point of care ultrasound advocated for the "Two-point" scan. This meant - look in one spot at the common femoral, then one spot in popliteal vein, and then call it quits. The idea is that if you don't see a DVT in these spots, there is unlikely a DVT elsewhere. Well...that turned out to not be exactly true. A study showed you will miss around 6% of DVTs that way. So now, we do two REGION exams. Following the common femoral and popliteal over a more extensive area. Therefore it came as a surprise when this study advocated for a single point exam! The main concept is that respiratory phasicity (the change in the flow of vein with respiration) should be present normally and if it is not - it means something is blocking the vein between your probe and the chest. So this study thought that if you have A) Full compression in popliteal vein AND B) Normal phasicity in the popliteal vein, then you could rule out a lower extremity DVT.


Methods

Patients enrolled from emergency department. Inclusion and exclusion criteria alluded to but not made explicit.

Checked single point scan by emergency residents or attending: Popliteal vein evaluated for compressibility and respiratory phasicity. If normal → considered negative for DVT. If either abnormal → performed exam of proximal veins of leg.

Compared to DVT exam performed by radiology residents.


Results

n = 347

  • 76 (21.9%) had DVT

  • 53 (69.8%) isolated to popliteal

  • 19 (25%) in both popliteal and femoral

  • 4 (5,2%) had isolated femoral DVT


The 1 point scan identified all DVTs. All isolated femoral DVTs lacked phasicity.

Of the people without DVT, 57 (20.9%) had abnormal phasicity. This prompted proximal vein evaluation, which in all cases was negative for DVT.


Limitations

We don't know the inclusion and exclusion. We don't know the full methods.

Since isolated femoral clots are rare and this study only included 4, this is not definitive evidence that this is a good strategy.

This concept doesn't really make sense anatomically, because of two problems.

  • You may still have phasicity if a proximal DVT has not completely occluded the vein

  • DVTs isolated to the deep femoral vein would not theoretically affect the phasicity in the popliteal vein since they are not continuous


Discussion/Conclusions

Seems risky but maybe phasicity could be sensitive enough that it will pick up proximal occlusions.

Too early to change practice, but maybe test this idea out yourself. Start with popliteal and see if this holds true in your scans.


2. Prediction of fluid responsiveness following cardiac surgery using Doppler renal resistive index


Background

The search for the perfect non-invasive measurement of fluid responsiveness continues. We want something that will select out a population that would benefit from more intravascular volume. This paper looks at a novel parameter for this purpose. The resistance index (RI) is something that is used commonly in doppler (although not usually in the point of care sector). The equation is this:

RI = (peak systolic velocity - end diastolic velocity ) / peak systolic velocity

Here's a video on obtaining the RI. The idea of this paper is that this index might be used to figure out who would be fluid responsive.


Methods

Patient population was adults undergoing cardiac surgery that required a pulmonary artery catheter. They excluded AKI, CKD IV-V, or atrial fibrillation.

They checked renal RI after surgery before and after a passive leg raise. Took the mean of three measurements. Compared to cardiac output as measured with thermodilution, performed at the time of doppler assessment. 10% increase in cardiac output considered responsive.


Results

n = 30

  • 9 patients were "responsive" to passive leg raise based on standard

  • no significant different in baseline RI between groups


Fluid responsive patients had greater negative change in RI during passive leg raise

Responders: -0.043 (IQR -0.051;-0.04)

Non-responders: -0.008 (IQR -0.032;0.015) p=0.004

There was association between change in RI and improvement in cardiac output following PLR: OR 1.87 per -0.01 change


Limitations

We don't know the full methods.

Very specific group of patients (post-cardiac surgery) - limits external validity.

Small sample size.

Results may have been significant, but the differences are so small that it seems it could easily fall within range of inter-rater reliability.


Discussion/Conclusions

Cool idea, not ready for prime time. We need a bigger study, broader population, and we need to know that the average POCUS user could accurately distinguish between these minute changes in RI.


3. Suspected small bowel obstruction in the emergency department accuracy of point-of-care ultrasound


Background

Ultrasound is actually pretty good at diagnosing small bowel obstruction (SBO). See this study for a review on diagnostics in SBO. There are only a few studies looking at this so far, so most people (including consultants) are hesitant to hang your hat on it. This article wanted to do a nice multi-center study in the emergency department to figure out the test characteristics.


Poop Sac 2.0 - the Ultrasound Podcast discusses POCUS for SBO


Methods

Prospective, multicenter, observational study

Patients in ED with suspected SBO

Exam performed by emergency resident, fellow, or attending

Compared to CT and discharge diagnosis


Results

n = 148

  • 52.7% had SBO


Sensitivity 88.5% (CI 79.2-94.6%)

Specificity 50.0% (CI 37.8-62.2%)

+LR 1.77

-LR 0.23


Most sensitive findings:

  • To-and-fro peristalsis 76.9%

  • Small bowel diameter >25mm 75.6%

Most specific finding:

  • Transition point (n = 23) 96.6%

Abdominal Xray less sensitive (72.5%) and more specific (79.0%). + LR 3.44, -LR 0.35


Limitations

We don't know the full methods

Results inconsistent with prior literature, where ultrasound is usually more sensitive and specific.


Discussion/Conclusions

It could be that ultrasound is not as good as we thought previously, or it could be that these authors are doing something different that makes the exam less accurate. Unlikely to change practice at this point.

Transition point is interesting finding not previously described. This may be a more specific finding signifying SBO.


Take Home Points

1. Don't change your practice based on abstracts.

2. One point DVT scan including phasicity - although it seems like this would miss significant proximal DVTs, none were missed in this small study.

3. Change in renal resistive index may correlate with fluid responsiveness, but differences are so small reproducibility seems a challenge.

4. A transition point may be highly specific for small bowel obstruction on POCUS.


Published on 10/23/17 06:00 AM
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