Category Archives: Abstracts

AAST 2019 #2: Predicting Abdominal Operation After Blunt Trauma – The RAPTOR Score

Patients with blunt abdominal injury, particularly those with seat belt signs, can be diagnostically very challenging. If the patient is stable and does not have peritonitis, CT scan is typically the first stop after the trauma resuscitation room. As many trauma professionals know, the radiographic findings can be subtle and/or not very convincing.

The trauma group at the University of Tennessee in Memphis sought to identify specific findings that might help us better identify patients that will need laparotomy. They retrospectively identified all their mesenteric injuries over a five-year period. A single blinded radiologist (is this an oxymoron or not?) reviewed all 151 patient images who underwent laparotomy, looking for predictors of bowel or mesenteric injury.  All of the predictors were then converted into a scoring system called RAPTOR (radiographic predictors of therapeutic operative intervention; kind of a stretch?). These predictors were then subjected to multivariate regression analyses to try to tease out if there were any independent predictors of injury.

Here are the factoids:

  • A total of 151 patients were identified over the 5 year period; 114 underwent laparotomy
  • Of the 114 operated patients, two thirds underwent a therapeutic laparotomy and the other third were nontherapeutic
  • There no missed injuries in the non-operated patients
  • The components of the RAPTOR score were culled from all the potential findings, and were determined to be
    • Multifocal hematoma
    • Acute arterial extravasation
    • Bowel wall hematoma
    • Bowel devascularization
    • Fecalization (of what??)
    • Free air
    • Fat pad injury (??)
  • Linear regression then showed that only three of these, extravasation, bowel devascularization, and fat pad injury to be independent predictors of injury
  • If three or more RAPTOR variables were present, then the sensitivity, specificity, and positive predictive values for injury were 67%, 85%, and 86%, and an area under the receiver operating characteristic curve (AUROC) of 0.91

The authors concluded that the RAPTOR score provided a simplified approach to detect patients who might benefit from early laparotomy and not serial abdominal exams. They go further and say it could potentially be an invaluable tool when patients don’t have clear indications for operation.

It looks like there are two things going on here at the same time. First, a new potential scoring system is being piloted. And second, a regression analysis is being used to examine the data as well. 

But first, let’s back up to the beginning. This is a retrospective study, with a relatively small size. This makes it far harder to ensure that the results will be significant, or at least meaningful. Use of a single radiologist can also be problematic, especially since many of the CT findings with this mechanism of injury are subtle. 

The reported performance of the RAPTOR score is a bit weak. The listed statistics show that it accurately identified only two thirds of those who needed an operation and 85% of those who didn’t. The AUROC for the regression is very good, though. Could a good old-fashioned serial exam scenario be better?

Bottom line: It will be interesting to hear the background on RAPTOR vs regression, and find our how the authors will use or are using these tools.

Here are my questions for the presenter and authors:

  • Why did you decide to create a scoring system that uses a set of variables that may be dependent on each other? Isn’t the regression equation better?
  • Has this information changed your practice? It seems that the two of the three regression variables are fairly obvious reasons to operate (active extravasation and devascularization). Do you really need the rest?
  • Has this study helped you decrease the non-therapeutic laparotomy rate for blunt abdominal injury?
  • And please define fecalization and fat pad injury!

I’m looking forward to hearing this presentation!

Reference: RADIOGRAPHIC PREDICTORS OF THERAPEUTIC OPERATIVE INTERVENTION AFTER BLUNT ABDOMINAL TRAUMA: THE RAPTOR SCORE. AAST 2019 Oral Paper 6.

 

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AAST 2019 #1: Survival Benefit Of Pelvic REBOA

Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) is one of the new, shiny toys in the trauma professional’s toy chest. Research papers on the topic are increasing exponentially, but human data was not even published until 2014! This is still a new device and we are trying to learn more about it.

The AAST set up an Aortic Occlusion for Resuscitation in Trauma and Acute Care (acronym is AORTA, ugh!) to help accumulate data for this not-often used technique. Hopefully, compiling comprehensive use and outcome data will speed our appreciation of the usefulness of this device.

A multi-institutional trauma group massaged the AORTA registry to examine the potential benefits of using the technique in patients with pelvic fractures leading to severe blood loss. They specifically looked for patients with the balloon inflated in Zone 3 to decrease bleeding from below the aortic bifurcation. Here’s a diagram of the zones:

The authors identified a total of 109 patients pelvic fractures with bleeding from below the bifurcation.

Here are the factoids:

  • The presenting patients arriving without CPR all had similar base deficit, lactate, and systolic BP. This shows us that the two groups are the same, but only for these three parameters. GCS was lower in the open aortic occlusion group. This could certainly contribute to a higher overall mortality in this group.
  • Overall mortality was significantly lower in the REBOA group that included those arriving with CPR in progress (35% vs 80% for open occlusion)
  • And when CPR patients were excluded, the mortality was significantly lower (33% vs 69%)
  • One in ten patients undergoing REBOA suffered vascular access complications (vascular repair required, limb ischemia, distal embolization, or amputation)
  • Complications among survivors were not different between the groups, nor were hospital or ICU lengths of stay or blood usage

The authors state that their data shows a “clear survival advantage” in those patients who undergo REBOA. Furthermore, this was accomplished without increasing systemic complications. They finally conclude that REBOA should be “strongly considered” for patients in shock due to pelvic trauma.

Not quite so fast here. There are several more factors in play than meet the eye.

First, a study that massages a REBOA database was generally constructed to see if REBOA is beneficial, especially in this time of rapid investigation. And it was performed by institutions who are using it regularly. This could introduce a significant degree of confirmation bias, since we all try to see what we already believe to be true (“REBOA is good”).

The authors are basing this “clear survival advantage” on overall mortality where only a few confounding factors have been controlled for. The GCS wild-card here is a perfect example. It could have considerably contributed to mortality in the open group, making it look bad. Who determined whether REBOA or open technique would be used, and why? This can have a major impact. What other factors might be present that are not even recorded in the database?

It is also stated that this increased survival was accomplished without increasing systemic complications. Perhaps, but that may be true of only the ones examined, or those recorded in the registry. Many may be missing. And what about the 10% incidence of limb issues in the REBOA group? This is a major problem and should not be glossed over. Although the patients that required a vascular repair were reported to do well, the others with ischemia or limb loss obviously did not.

Bottom line: Reading abstracts is like reading scientific papers, only more difficult because information is missing due to length limitations. Look at the title. Look at the conclusions. But don’t believe anything until you can understand every one of the results listed. And be sure to think about all the things that have to be left unsaid because of the size of the abstract! 

Having said all that, I still have to be careful that this doesn’t trigger my own confirmation bias. My take is that REBOA is still an investigational device. We need further comprehensive data to make sure that survival and safety are properly balanced.

Here are some questions for the presenter and authors:

  • The abstract describes the number of cases identified as 109; 84 REBOA and 25 open occlusions of the aorta. This seems to include patients undergoing CPR upon arrival, and these are excluded from some of the statistics. However, I can’t get the mortality percentages to match for the group that supposedly includes CPR patients. For example, the overall REBOA (includes CPR) mortality percentage is 35.17%. Multiplying this by 84 gives 29.5 patients. But multiplying the 33.33% mortality (CPR-excluded group) by 84 yields 28 patients. So are the 109 patients listed in the abstract the CPR-excluded group or not?
  • The open aortic occlusion group had a lower GCS. Did you look at how this might have contributed to the higher observed mortality? Although numbers are already low, is there any way to match for this to clarify the picture?
  • Do you have any information yet on longer term outcomes in the two groups? This will become very important as we come to balance raw survival with quality of life and complications.

Great abstract! I’m looking forward to the presentation, and hopefully more answers!

Reference: SURVIVAL BENEFIT FOR PELVIC TRAUMA PATIENTS UNDERGOING RESUSCITATIVE ENDOVASCULAR BALLOON OCCLUSION OF THE AORTA: RESULTS OF AAST, AORTIC OCCLUSION FOR RESUSCITATION IN TRAUMA AND ACUTE CARE SURGERY (AORTA) REGISTRY. AAST 2019 Oral Abstract #3.

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Coming Up! AAST 2019 Abstract Reviews!

It’s that time of year again. The 2019 Annual Meeting of the American Association for the Surgery of Trauma (AAST) is only two weeks away! I’ll be selecting a number of interesting abstracts (oral, poster, and perhaps a few quick shots) to review here.

My focus will be on abstracts that offer new information or interesting insights into old problems. I’ll pick them apart, looking at their strengths and weaknesses. Finally, after rendering my opinion of their import, I’ll list a number of questions for the authors or presenter to consider. Who knows, they may be asked some of them at the meeting?!

Enjoy, and feel free to provide your own comments here!

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EAST 2019 #13: Geomapping Helicopter transports

Helicopter EMS (HEMS) transports are a valuable yet very expensive resource. Unfortunately, many state trauma systems or local EMS agencies do not provide specific guidance for best use. A group at the University of Alabama in Birmingham performed a geospatial analysis of helicopter transports in their area to determine the efficiency of HEMS operations.

This group created a sort of “heat map” that showed the number of transports overlaid on a geographical map of their catchment area. It included HEMS transports over a 6-year period directly from the scene. Drive and flight times were calculated, and the latter also included flight time to reach the scene.


Here’s the heat map showing the entire state of Alabama. The approximate location of Birmingham is indicated in yellow.

Here are the factoids:

  • Nearly 3000 patients were identified, and 1911 had scene locations recorded so analysis could be performed
  • 35% of patients had minor injuries with ISS 1-8 (!!)
  • Median flight time was 58 minutes, and median drive time was only 65 minutes
  • In 28% of cases, drive time would have been shorter than flight time when considering time for the helicopter to reach the scene
  • Conclusion: over one fourth of patients might have arrived at the hospital more quickly by ground ambulance

Here are some questions for the authors and presenter to consider in advance to help them prepare for audience questions:

  • Why include time for the helicopter to reach the scene but not a ground ambulance? Doesn’t this stack the deck in favor of ground transport?
  • Was there any correlation between scene proximity and high ISS? This might have been a reason for calling the helicopter.
  • Did you see any patterns in the low ISS group? This could provide insight into the EMS thought processes. These patients are potentially the low hanging fruit to direct educational activities to reduce HEMS use.

This is thought-provoking work and I look forward to hearing all the details!

Reference: Use of helicopters for retrieval of trauma patients: a geospatial analysis. EAST 2019, Quick Shot Paper #26.

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EAST 2019 #11: Thawed Plasma And Rural Trauma Centers

A massive transfusion protocol must be available at all trauma centers, large and small, urban and rural. In an ideal setting, attempts are made to keep the ratios of red blood cells to plasma transfused somewhere between a 1:1 and 2:1 ratio. Unfortunately, many hospitals do not keep any thawed plasma because of its 5-day shelf life, so they must resort to thawing it on demand. This process is slow and may take 20-40 minutes, so it is often difficult for these centers to keep within the optimal ratios.

The group at the Guthrie Clinic, a Level II trauma center in northern Pennsylvania, tried a novel approach to thawed plasma availability: keeping two units continuously available in the ED for trauma use only. After three days, these units were returned to the blood bank for general use and were replaced with new ones. They reviewed their one year experience with wasted plasma and compared it with the two years prior to implementation.

Here are the factoids:

  • The blood bank thawed 1127 units during the study period; 274 units were placed in the trauma bay
  • There was a significant increase in waste and cost of wasted products
  • Yet the authors did not find an increase in the relative cost of plasma waste
  • The average cost to maintain access to plasma in the trauma bay was $117 per month
  • The authors concluded that the increased waste and cost were insignificant compared to the cost of total blood bank waste (?)

Here are some questions for the authors and presenter to consider in advance to help them prepare for audience questions:

  • What do all the terms mean, like relative cost? I’m confused that the cost of waste is significantly higher, but not the relative cost. Please explain in your presentation.
  • Is the $117/month to maintain access just for the refrigerator itself and any other support hardware or software? It’s not clear if this includes any part of the blood product cost.
  • Why not keep the plasma in the blood bank? Even though it might still be wasted, couldn’t you save the $117 monthly and avoid the hassle of trying to find a cubby to put the ED blood refrigerator in?
  • Why is 3 days your magic number? Did you consider doing a simulation after you completed the study to see what would have happened if you picked 2 or 4 days in the ED instead?

This is a very creative approach to stocking perishable goods that are infrequently used. I look forward to hearing the presentation.

Reference: A novel protocol to maintain continuous access to thawed plasma at a rural trauma center. EAST 2019, Quick Shot Paper #14.

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