Category Archives: Abstracts

EAST 2019 #1: Predicting Outcome After Brain Injury

Here’s the first abstract I’ll review from the EAST 2019 Annual Assembly in January.

This one comes to us from the University of Arizona system, and specifically from Tucson. The senior author has an interest in traumatic brain injury (TBI) and geriatric trauma, so it’s not surprising to see this abstract that fuses the two. The aim was to create a new tool to predict mortality in patients who had sustained a TBI.

The authors devised a score, the Brain Trauma Outcome Score (BTOS) using three variables: age, injury severity score (ISS), and presence of blood transfusion. Furthermore, this was used to create a Brain Trauma Outcome Score (BTOS), by dividing the BTOS by the GCS. These equations were developed and tested using data sets from two years worth of TQIP data. I know, lots of acronyms, but stay with me. After generating the equations for GTOS and BTOS from one TQIP dataset and testing against another, both of these systems were checked for discriminatory power by generating receiving operator characteristic curves.

The authors found that the tested BTOS was better at predicting mortality than the tested GTOS. They concluded that “BTOS can accurately predict in-hospital mortality in all TBI patients.” Seems like a pretty bold assertion.

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

  • Be aware that some typos crept into the final copy. When preparing abstracts, try not to use special characters (i.e. +) as they may not be generic enough for the commercial printing software used to prepare final copy. This is similar to avoiding video or links to YouTube videos in slide sets. I was able to figure out what the question marks really were (I think), but make sure the audience does, too.
  • Why did you even think to create this model? Some new “systems” are just wild guesses, and sometimes it’s even possible to find one that appears to have a significant correlation with reality. What was the rationale that prompted you to combine ISS, age, blood, and GCS? Did your clinical experience suggest this? Papers on related prediction systems? Then what?
  • Is validating your test data using other patients from the same dataset legitimate? Shouldn’t they be very similar since they are in the same 2-years of data? This could make the system less accurate when applied to a very different patient cohort.
  • The GCS range studied was very high and narrow. If I read the abstract correctly, the median was 14-ish with a range from 12-15. These are mostly mild TBIs, so why were they dying anyway? And if the formula for GTOS was derived using predominantly mild TBI data, how can it possibly work well for moderate and severe? And I still worry that patients were dying of problems unrelated to TBI.
  • Make sure you clearly explain your methods to the audience. Some are not well versed in ROC curves, and many will not understand the nuances and potential pitfalls of developing and validating numerical systems like this. It’s easy to lose them, so make sure you are clear and concise in your explanations.
  • How do you see a system like this being used in the future? It’s nice to have some appreciation of the practicality, and an assurance that this isn’t just an academic exercise.

I enjoyed the abstract, and look forward to hearing it in person next month!

Reference: The Brain Trauma Outcome Score (BTOS): Estimating mortality after a traumatic brain injury. EAST 2019, Paper #6.

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Starting Next Week: EAST 2019!

The 32nd Annual Assembly of the Eastern Association for the Surgery of Trauma (EAST) is just around the corner. The meeting starts January 15 in Austin, TX.

I traditionally choose some of the abstracts to presented that I find particularly interesting. I’ll dissect them here on the blog, and provide suggestions to the authors on how to prepare for questions they might receive from the audience at the meeting.

Starting next Monday, and continuing through the meeting in Mid-January, I’ll be posting one critique per day. Tune in and enjoy!

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Best of AAST #11: The Need For Trauma Intervention Score (NFTI)

The Trauma Measurement Workgroup at Baylor University in Dallas has been working on a new indicator for identifying major trauma. In a paper published in the Society of Trauma Nursing last year, they determined that six trauma registry variables best identified these patients:

  • transfusion of packed cells within 4 hours of arrival
  • discharge from ED to OR within 90 minutes of arrival
  • discharge from ED to interventional radiology
  • discharge from ED to ICU with a stay > 3 days
  • mechanical ventilation within 3 days, not including OR or procedures
  • death within 60 hours of arrival

Traditionally, Injury Severity Score (ISS) has been used to measure anatomic injury, the Revised Trauma Score (RTS) to quantify physiologic derangement, and their combination (TRISS) to estimate survival.  The authors postulate that physiologic reserve is another determinant of survival, and that NFTI might provide a way to quantify this reserve. One of the QuickShot presentations at the AAST meeting demonstrates how the authors applied this metric.

A multi-institutional data collaborative collected information on more than 88,000 across 35 trauma centers. A complicated mathematical and statistical analysis was carried out, testing how well high ISS (>15), low RTS (<4), and NFTI+ (at least one NFTI variable) predicted mortality, complications, full trauma team activation, length of stay, and procedures performed within 3 days of arrival.

The authors found that NFTI was significantly better at predicting all the outcome variables except full trauma activation than ISS or RTS. And it was still pretty good at that one.

Bottom line: So what does all this mean? The design and analysis of all the numbers is sound. The only thing I take issue with is the assumption that NFTI reflects the “reserve” that a patient has available to combat serious injury. The authors postulate that NFTI is not affected by frailty and comorbidities like ISS and RTS are. I have not seen the manuscript, so perhaps the authors explain the rationale there. But it seems like a stretch. 

What happens if we remove that assumption? Then this study becomes a comparison of a new way to predict resource utilization and/or survival vs ISS and RTS. It uses future variables (as does ISS), so it is difficult to apply this information on patient arrival to treat them any differently, until the first NFTI factor is triggered. But it does predict them well. I think there is considerable potential for NFTI, but we just need more work to make it more useful as early as possible.

Reference: The need for trauma intervention (NFTI) defines major trauma more accurately than injury severity score (ISS) and revised trauma score (RTS): data from a collaboration of 35 adult trauma centers. QuickShot presentation #9, AAST 2018.

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Best of AAST #10: Pediatric Contrast Extravasation And Pseudoaneurysms

There is a significant amount of variation in the management of pediatric solid organ injury. This is well documented between adult and pediatric trauma centers in t, but also apparently between centers in different countries. A poster from a Japanese group in Okinawa Japan will be presented this week detailing the relationship between contrast extravasation after spleen or liver injury and pseudoaneurysm formation.

In adults, the general rule is that pseudoaneurysms just about anywhere slowly enlarge and eventually rupture. This group sought to define this relationship in the pediatric age group. They performed a multi-center observational study of retrospectively enrolled children, defined as age 16 and less. Those who had contrast extravasation on initial CT were monitored for later pseudoaneurysm formation.

Here are the factoids:

  • 236 patients were enrolled across 10 participating centers, with about two-thirds having liver injury and the remainder with splenic injury
  • 80% of patients underwent followup CT scan (!!)
  • 33 patients (15%) underwent angiography (!!!!)
  • 17 patients with CT scan (2%) had pseudoaneurysm formation and 4 of them had a delayed rupture
  • Overall, pseudoaneurysms occurred in 29% of those with contrast extravasation and 5% without extravasation
  • The authors concluded that contrast extravasation was significantly associated with pseudoaneurysm formation after adjusting for variables such as ISS, injury grade, and degree of hemoperitoneum

Bottom line: This is an abstract, so a lot is missing. What was the age distribution, especially among those who underwent angiography? Was the data skewed by a predominantly teenage population, whose organs behave more like adults? The abstract answers a question but ignores the clinical significance.

For those trauma professionals who routinely care for pediatric patients, you know that contrast extravasation in children doesn’t act like its adult counterpart. Kids seldom decompensate, and for those who are mistakenly taken for angiography, the extravasation is frequently gone. The authors even admitted in the conclusion that aggressive screening and treatment for pseudoaneurysm was carried out.

The real question is, what is the significance of a solid organ pseudoaneurysm in children? Based on my clinical experience and reading of the US literature, not much. Of course, there is a gray zone as children move into adulthood in the early to mid-teens. But this does not warrant re-scanning and there should be no routine angiography in this age group. Contrast extravasation in pediatric patients warrants close observation for a period of time. But intervention should only be considered in those who behave clinically like they have ongoing bleeding. 

Reference: Association between contrast extravasation on CT scan and pseudoaneurysm in pediatric blunt splenic and hepatic injury: a multi-institutional observational study. Poster 31, AAST 2018.

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Best of AAST #9: Popliteal Atery Injury Repair

Injury of the popliteal artery is potentially devastating. Since this vessel is essentially and end artery, any complication resulting in thrombosis can result in limb loss. Traditionally, significant injuries have been treated with open repair and/or bypass. However, endovascular therapies have been making inroads in this area. Short-term outcomes appear to be equivalent. But what happens in the long term? Is one better than the other?

Scripps Mercy in San Diego (yes, same as yesterday’s abstract!) performed a retrospective review of the same California state discharge database. This time, they focused on patients with popliteal artery injury, and the attendant complications of fasciotomy and amputation. They stratified the patients into open and endovascular groups.

Here are the factoids:

  • 769 patients with popliteal artery injury were identified over an 8-year period
  • 59% were managed with an open operation, 4% using endovascular techniques, 2% combined, and 34% nonoperatively
  • Fasciotomies were performed significantly more often in the open group (41% vs 19%)
  • More amputations were performed in open cases, but this was not significantly different (11% vs 3% [1 patient in the endovascular group])
  • Embolism or thrombosis was significantly more likely during the first admission in endovascular or combined endo/open cases
  • Patients requiring both endo and endo+open procedures  were 5x more likely to undergo a later amputation, and 4x more likely to die after discharge

Bottom line: First, remember the limitations of this study: (very) small numbers, and a large database that precludes teasing out details. It suggests that open repair of popliteal injury is superior to endovascular due to higher thrombosis/embolism and amputation rates. Performing a fasciotomy is somewhat subjective, and may be done by surgeon preference to protect the limb. But amputation is more objective.

Unfortunately, we will not get anything more definitive any time soon. This 8-year analysis of a huge state database yielded only 769 cases, or 96 per year. In a state with 39 million people. That’s three injuries (reported) per million people per year. We will never generate a study that will tell us the full answers. But in the meantime, consider endovascular repair of popliteal artery injury only in patients for whom an open procedure is more challenging or risky (e.g. obesity, associated wounds).

Reference: Outcomes for popliteal artery injury repair after discharge: a large-scale population-based analysis. Session XXII Paper 55, AAST 2018.

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