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Abstracts, Technology

Best Of AAST #10: The Hybrid ER Room?

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The next abstract is an interesting demonstration of the use of technology is trauma resuscitation. Pretty much all technology imaginable. It details the use of a “hybrid ER” room, which combines resuscitation space with all sorts of imaging and even interventional angiographic procedures. Here’s an image of the room when it was first written about in 2012.

A = CT scanner   B = CT exam table   C = movable C-arm   D = monitor screen   E = ultrasound   F = ventilator

This setup was installed at Osaka General Medical Center in Japan nearly 10 years ago. The authors have written occasional papers about it, and have now performed a study on its impact on trauma patient survival. They studied major trauma patients during two time periods. The first was pre-installation (2007-2011), and the second started immediately after installation (2011-2020). They specifically looked at 28-day mortality, and tried to tease out the relation to injury severity.

Here are the factoids:

  • About a thousand patients were studied, 348 in the pre (conventional) group and 702 in the post (hybrid) group
  • 28-day mortality was significantly lower in the hybrid group
  • Using a fancy statistical test (cubic spline analysis), they showed that 28-day mortality sharply decreased 200 days after installation of the hybrid ER
  • Mortality decreased disproportionately more in the hybrid ER as the injury severity score (ISS) increased

The authors concluded that the hybrid ER may have improved survival, especially in the more severely injured patients.

Here are my comments: Hmm. This is an association study that only looks at one variable, the new hybrid ER room. How many other variables may have a potential impact on survival? And how have those variables changed over the past 11 years? I worry that the study premise is too simplistic, but it certainly makes this unique resource look good.

Here are some questions for the presenter and authors:

  • How did you select your patients? You describe about 1,000 patients over 11 years, which is only about 100 per year. What about all the others?
  • What is it about the hybrid room that you think confers such a survival benefit to your patients? It seems to work for all patients, blunt or penetrating, badly hurt or not. What’s the magic?
  • Do you see the same effect for patients who were treated at other hospitals first and then transferred? The extra time that passed could decrease survival in severely injured patients.
  • Please explain cubic spline analysis clearly. I always worry when super-fancy statistical tests are needed to detect a difference. Why was it needed in this case?
  • Why did it take 200 days to see an effect from the installation of the hybrid ER? What happened at that point in time?
  • Please explain how the actual survival is so much better than predicted for ISS=75 patients. Your graph shows an actual survival of about 22%, as opposed to the 3% in your conventional ER. That is a massive improvement! How do you do it?

As you can see, I’m a bit uncertain about how this works and how the lessons can be applied to other centers. This is a unique resource, and the rest of the world needs to know a lot more about it before deciding to try it out themselves.

Abstracts, Complications

Best Of AAST #9: Blunt Carotid And Vertebral Injuries

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Blunt carotid and vertebral artery injuries (BCVI) are an under-appreciated problem after blunt trauma. Several screening tools have been published over the years, but they tend to be unevenly applied at individual trauma centers. For an unfortunate few, the only indication of BCVI is a stroke while in hospital.

The overall incidence of BCVI is thought to be small, on the order of 1-2%. But how do we know? Well, the group at Birmingham retrospectively reviewed every CT angiogram (CTA) of they did in a recent two year period. They did this after adopting a policy of screening all their major blunt trauma patients. Each patient chart was also evaluated to see if they met any of the criteria for the three commonly used screening systems.

Here are the factoids:

  • 5,634 of 6,800 blunt trauma patients underwent BCVI screening with CTA of the neck
  • 471 patients (8.4%) were found to have BCVI
  • Here are the accuracy statistics for the three screening systems

Here are my comments: The authors found that the incidence of BCVI is about 8x what we previously thought. What we don’t know is the percentage of these patients that go on to cause stroke or other neurologic deficits. But this is somewhat frightening.

Even more frightening is that the screening systems that we rely on fare so poorly. The Denver and Modified Memphis criteria have a true positive rate that is the same as a coin toss. And even if the patient meets none of the criteria in any system, about 5% BCVI will sneak through (NPV 95%).

So the question becomes, do we all perform universal screening for blunt trauma? Or do we still use one of the three systems and keep our fingers crossed that the ones we miss will not progress? Or maybe just give everybody an aspirin a day for a while. And still keep our fingers crossed!

Here are some questions for the presenter and authors:

  • Why did you decide to implement a universal screening protocol in the first place? Bad experience(s)?
  • Do you have any screening recommendations other than to screen everybody? How do you decide which blunt trauma patients to screen? Every car crash? What level of fall? The devil is in the details!

This is an easy to follow paper with a solid analysis and real world implications. Excellent work!

Abstracts, Complications

Best Of AAST #8: Duplex Screening For DVT

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To screen on not to screen, that is the question. If you do more testing, you will find more cases. But does it make a difference clinically? Sounds like some of the questions coming up in our current discussion of the Coronavirus. But that’s what we really need to know.

The group at Intermountain Medical Center in Salt Lake City performed a 2 ½ year randomized, prospective study of screening duplex ultrasound of the lower extremities vs no screening study. They used the Risk Assessment Profile (RAP) developed by Greenfield, first published in 2000. Any patient at moderate or higher risk for DVT (RAP score >5) was enrolled in the study. They were randomized into two groups: a screening group who received duplex scans on days 1, 3, 7, and then weekly, and a “no routine screening” group. All patients received chemoprophylaxis per the trauma service’s existing protocol.

The RAP score is a 17 factor scale that assigns a specific number of points based on underlying medical conditions, iatrogenic factors like central lines or transfusions, injury-related factors, and age.

Here are the factoids:

  • A total of 3,236 trauma patients were identified, and the 1,989 who were at moderate or higher risk for DVT were evenly randomized to screening vs no screening
  • There were no differences in age, sex, BMI, mechanism, ISS, or length of stay between the two groups
  • The incidence of DVT was 15% in the screened group vs 1.7% in the no screening group

The authors concluded that screening diagnoses more DVT, most of which is below the knee. And they also noted that screening identified DVT more often than clinical exam alone, but does not result in fewer PE or deaths. They suggest that more work needs to be done to identify exactly who benefits from duplex screening the most.

Here are my comments:

Finally, an easy to follow and well-designed study! But I think some of the results may be missing from the abstract. That section cuts off in the middle of some of the statistics, and there is no mention of the clot location or PE/mortality rates mentioned in the conclusion.

I also worry that a thousand patients in each group may not be enough. We are working with low incidence end points like PE and death, and this is an association study with many potential confounders/factors that may not have been recorded. I generally like to see the ability to detect a minimum of a 2x effect. So if the incidence of PE is 1.5%, I like to see the ability to detect a difference if the other group is 3%.

And speaking of study size. The RAP score was first described in 1997 and was a pilot study. They drew their conclusions from only 53 patients, and the only risk factor that they could show that was a statistically significant predictor of DVT was age. They concluded that surveillance of patients with RAP > 5 was warranted. This abstract builds upon this work, but is trying to say that maybe we don’t need to do duplex scans.

Here are my questions for the presenter and authors:

  • Is there some text missing from the end of the results section of the abstract? It seems to end unexpectedly, and some things are mentioned in the conclusions that are not in the results.
  • Why did you choose the RAP score? There are other risk assessment tools available out there. What is so special about RAP?
  • Is your sample size large enough to detect differences in incidence of PE or death? My back of the envelope calculations suggest at least 1,500 patients would be needed in each group.
  • How long did you follow patients to determine if they had PE or death? Until they were discharged? Later than that?  This makes a big difference in the eventual incidence of these outcomes.
  • Based on what you found, is there any value to treating asymptomatic proximal DVT? It sounds like you are saying that screening is not needed at all because PE and death are the same. Isn’t there value in treating proximal DVT if you find it?

This abstract certainly got me thinking! I am looking forward to the presentation and discussion of this abstract!

Reference: Head in the sand? The value of routine duplex ultrasound screening for venous thromboembolism in the trauma patient: a randomized Vanguard trial. AAST 2020, Oral Abstract #16.

Abstracts, Resuscitation

Best Of The AAST #7: TXA And Thromboembolism

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The use of tranexamic acid (TXA) in trauma patients has escalated dramatically since the CRASH-2 trial was published ten years ago. It has become a frequent addition to the massive transfusion protocols used by trauma centers. And we are now even seeing TXA given by prehospital provides when life-threatening bleeding is suspected.

This drug is popular because it is inexpensive (~$100/dose) and is thought to be safe. However, some trauma professionals have been concerned about thrombotic side effects since TXA is a finbrinolysis inhibitor.

The group at the Mayo Clinic performed a retrospective study of seven years of their own data to determine if the concern for thrombotic complications was warranted. They specifically evaluated in-hospital mortality and thrombotic events up to 28 days after injury.  They also scrutinized outcomes in patients who received only the bolus TXA injection, but not the infusion.

Here are the factoids:

  • A total of 848 patients were included in the study, but there was no information as to what the inclusion criteria were
  • Only 212 received TXA; the other 636 were considered the control group, and there were no differences in age, sex or mechanism of injury
  • Thrombotic events occurred in 13% of the TXA patients and only 6% in the control group, which was statistically significant
  • Specific thrombotic events in TXA vs non-TXA patients: DVT was 8.5% vs 3.5% (significant), pulmonary embolism was 3.8% vs 1.9% (NS), MI was 1.9 vs 0.4% (NS), stroke was 2.4% vs 1.1% (NS)
  • Thrombotic events occurred more frequently in patients who received both doses of TXA (23%) vs just the bolus (10%), and this was also significant
  • In-hospital mortality was 21% with TXA vs 10%, which was not significantly different, controlling for confounders

The authors concluded that TXA administration was associated with higher rates of thrombotic events. They went on to state that TXA should not be routinely given for trauma patients in the community setting.

Here are my comments:

This is a bold recommendation from this very small study. The CRASH-2 trial was randomized and placebo controlled, and analyzed their experience with 10,000 subjects in each arm. This retrospective study has only  212 TXA vs 636 control patients. Big difference.

The authors attempt to match the TXA patients with controls. They controlled for age, sex, mechanism, and ISS. But it does not appear that there was any control for injuries known to increase the risk of thrombotic events like spine and pelvic fractures.

And why look at a full 28 day interval for thrombotic events? I would expect most of these events to occur in the first few days. Including an entire month in the study allows thrombotic events from other causes to creep in.

Here are some questions for the presenter and authors:

  • Please comment on how the small numbers in your study may have an impact on the results.
  • What were the selection criteria for your 848 patients? Were they all of your trauma activation patients? If not, is there some selection bias possible?
  • DVT appears to be the driver for your “significant” number of thrombotic events. Yet the other events (MI, stroke, PE) were not significantly different. This seems counter-intuitive, since the DVT numbers themselves numbered only about 20 in each group. Please describe the statistics you used to derive this conclusion.
  • Did you look at the incidence of injuries that are known to increase the risk of thrombotic events in the two groups? If there was an excess of pelvic or spine fractures in the TXA group, this might not be picked up in your analyses and could skew your data.
  • Why did you include thrombotic events for a full 28 days after injury? This allows for later events caused by factors other than the TXA. Show us a redo of your analysis using 5 or 7 day thrombotic events.

These are interesting numbers, but I have to admit that I am skeptical. I’m not clear how community hospital administration of TXA makes it more likely associated with thrombotic events. I will definitely be listening intently to this presentation. And probably asking these questions.

Reference: Risk of thromboembolic events after the use of TXA in trauma patients. AAST 2020, Oral Abstract #15.

General

Best Of AAST #6: Timing Of Venous Thromboembolism Prophylaxis

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Venous thromboembolism (VTE) and pulmonary embolism (PE) have caused major problems for trauma professionals for at least 50 years. Interestingly, despite advances in chemical and mechanical prophylaxis, the mortality rates for both have remained about the same.

The group at St. Joseph Mercy Hospital in Ann Arbor looked at the timing of start of VTE chemoprophylaxis. They were curious as to whether the start time made a difference in mortality. They reviewed a collaborative database with 12 years of data, tallying information for all trauma patients who were admitted for at least 48 hours.

Here are the factoids:

  • Over 89,000 patients were analyzed; 1.8% developed VTE and 1.9% died (?)
  • Delay in starting chemoprophylaxis increased the risk of VTE (see figure)
  • Delaying chemoprophylaxis beyond 48 hours was associated with increased mortality and increased incidence of VTE

The authors concluded that early initiation of chemoprophylaxis reduces mortality and thrombotic complications.

Here are my comments: Unfortunately, I’m not entirely clear about the details of the abstract. This frequently happens because the authors have to strain to fit all of their ideas in a finite amount of space.

First, it’s a large database study, so it’s difficult to ensure that all the factors you want to study have been included in it. Somebody else designed it years ago, so you get what you get.

I’m a little confused about the incidence of complications and death. They are both about the same number (1.8%). Typically, VTE incidence is a few percent and death from PE is less than 1%. The death number seems high, unless it includes some other type of death.

The VTE incidence vs time graph is very interesting, although the goodness of fit looks a little off toward the right side. It looks like it could easily be a little lower.

Finally, segregating time periods into two 24-hour periods (0-24 hours, 24-48 hours)and one 72-hour plus one (48-120+ hours) seems like it might bias your data. The longer that last period, the greater chance that each patient will develop VTE or die.

Overall, the numbers in Table 1 are noted to be statistically significant, but clinically they appear to be very similar.

Here are some questions for the presenter:

  • Please explain the mortality numbers (1.9%). What did these patients die of? A pulmonary embolism? Something unrelated? This number seems high, since it is equal to your VTE incidence.
  • Tell us about the risk adjustment you used to calculate mortality rates. What patient factors were available to you? Are there others that might have been helpful to have in the database?
  • What tool did you use to fit the curve in Figure 1? The right side looks considerably higher than the data bars would suggest. Please be sure to explain all of the statistical techniques you used, as they were not fully covered in the abstract.
  • What was the impact of cramming 3 days of data into your last cohort? Wouldn’t this be expected to yield higher incidences of VTE and death?

I agree that VTE prophylaxis is best started early, but I need a wee bit more information. I’m intrigued by the paper, but I think you will have to spend some time explaining how you designed the analysis so we can all understand.

Reference: Association of timing of initiation of pharmacologic venous thromboembolism prophylaxis with outcomes in trauma patients. AAST 2020, Oral Abstract #14.