Abstracts

Best Of EAST #5: Keeping Blood From Going Bad

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What goes around comes around. Whole blood was the only transfusion product available until about 60 years ago, when the whole blood banking system switched to fractionating blood products. Now we are discovering the benefits of whole blood again. The military has been using fresh whole blood for some time. As civilians, we’ve had less access to whole blood. But once obtained, it must be used within 21 days. This is half the storage time for the usual bag of packed red cells, and may result in some waste of this valuable product.

The group at the University of Cincinnati wondered if fractionating and preserving an expiring bag of whole blood might extend the life of those red cells. They obtained 21- day old (expiring) whole blood and separated the red cells, preserving them using the usual technique. They then analyzed the cells weekly until expiration at 42 days for viability, storage damage and coagulation status.

Here are the factoids:

  • The number of units tested was not listed in the abstract
  • Damage from storage of the extracted red cells appeared to be consistent with normal damage expected from packed red blood cells
  • When mixed with plasma with a 1:1 ratio, clotting time, clot formation time, and maximum clot formation did not change as the salvaged cells aged

The authors concluded that the salvaged cells aged just like packed RBCs. They suggested that this may provide a method for extending the life of whole blood and allowing transfusion into patient in hemorrhagic shock.

My comment: This is an intriguing paper and suggests a way of extending the life and use of valuable whole blood. It appears to have been well done and analyzes standard markers of red cell dysfunction. However, the authors did not provide the number of units they tested. This is critical, since they are trying to show that the values tested are statistically the same (no difference between packed RBCs and those salvaged from whole blood). Some of their comparison numbers appear very different, but are not statistically significant. I worry that the number of units tested might be too small to show a difference.

Here is my question for the authors and presenter:

  1. Exactly how many units of whole blood did you use in this study? And did you do a power analysis to ensure that you don’t have a Type II error (false negative) with the “not significant” results?

This is a great idea and stands to save money and stretch our supply of blood!

Reference: Save it – don’t waste it! Maximizing utilization of erythrocytes from previously stored whole blood. EAST Annual Assembly abstract #6, 2020.

Abstracts, Complications

Best Of EAST #4: Cannabis And Venous Thromboembolism

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Cannabis and cannabidiol (CBD) are all over the news these days. CBD is legal everywhere, and it seems that more states are legalizing cannabis every few months. There are a few hints in PubMed that cannabinoids (THC) may have some impact on clotting, possibly causing hypercoagulability.

The group at the University of Arizona in Tucson decided to look into this in trauma patients. They did a two year scan of the TQIP database and stratified patients based on their THC status. They matched up THC positive and negative patients and examined thromboembolic events (deep venous thrombosis, pulmonary embolism, stroke, MI) and mortality.

Here are the factoids:

  • Nearly 600,000 patients records were in the database pull, but only 226 patients were THC+
  • They were matched at a 1:2 ratio with similar THC – patients (452)
  • No differences were found in the usual demographics, injury severity, use of DVT prophylaxis, and hospital length of stay
  • The THC+ group had a significantly higher incidence of overal thromboembolic complications (9% vs 3%)
  • Both DVT ( 7% vs 2%) and PE (2.2% vs 0.2%) were significantly higher in the THC+ group
  • No differences were seen in strokes or MI

The authors concluded that THC increases the risk of DVT and PE and that early identification and treatment for thromboembolic complications is required to improve outcomes in this high risk subset of trauma patients.

My comment: Seems compelling, right? But this is one of those abstracts that you have to read really closely. You have two groups of patients that are being compared, and a few statistical differences were found. The groups are small, but even so these differences are great enough to reach statistical significance. Great!

But, now step back and look carefully at the larger patient group. There are almost 600,000 patients there, but am I to believe that only 226 patients (0.04%) were using cannabis? According to recent statistics, approximately 8% of the US population currently uses marijuana. So in theory, about 47,500 patients in the TQIP sample should have tested positive. For whatever reason, this data point was not collected. Could data from the other 47,274 have changed the study result? Probably. 

Here are my questions for the authors and presenter:

  1. What was the impetus for this study? I was not aware of clotting issues due to THC and there is little in the published literature. I’d love to hear some history and be able to read more about this.
  2. What about the long time interval that a patient will test THC+ after partaking? THC remains in body fat for a month or more, and the qualitative test commonly used will provide a positive for weeks after the last use. How long do the thrombogenic effects of THC last? The THC+ result recorded in the dataset could be from THC use well before the traumatic event.
  3. How do you think your small sample of THC+ patients impacts your results given the much larger number of expected marijuana users in the sample?

This is intriguing work. Let’s here more!

Reference: Impact of marijuana on venous thromboembolic events: cannabinoids cause clots in trauma patients. EAST Annual Assembly abstract #4, 2020.

Abstracts, Thorax

Best Of EAST 2020 #3: Rib Fixation In The Elderly

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Elderly falls have reached epidemic proportions. Although the most common injury from these falls is rapidly become head injury with or without intracranial blood, rib fractures are a close second. Treatment of rib fractures usually involves multiple interventions such as pulmonary toilet, multimodal pain management, and therapies to enhance mobility. And in some cases, operative fixation is entertained.

Rib fracture fixation has typically been used in patients who are dependent on a ventilator due to their fractures, or have significantly displaced or very painful fractures. There is little data on the impact of using rib plating in elderly patients. The group at New York Presbyterian Hospital in Queens NY analyzed one year of TQIP data to assess the impact of this technique in trauma patients older than 65.

They reviewed the data, looking at mortality, intensive care unit and hospital lengths of stay, tracheostomy, and pneumonia rates. They matched patients who had rib fixation with similar patients who did not. They then sliced and diced the data to see if there were differences in these outcomes with early vs late (> 48hrs) repair.

Here are the factoids:

  • The authors obtained data on almost 14,000 patients meeting study criteria, but of those only 278 underwent rib fixation and 220 were eligible for matching
  • Overall, patients who underwent fixation tended to have higher rates of flail chest, earlier intubation, higher injury severity score, and increased intensive care unit admission rates
  • Mortality for all patients who underwent fixation was significantly lower than those who did not (4% vs 10%)
  • The early fixation group had significantly fewer ventilator associated penumonias, shorter ICU length of stay (6 vs 10 days) and shorter hospital length of stay (9 vs 15)
  • There were no differences in mortality or ventilator days

The author’s conclusions matched the bullet items above.

My comment: This is one of those papers that demonstrates something that we should have already recognized. I wish I had thought of it! It points us toward considering this procedure in our elderly rib fracture patients. Even though patients undergoing fixation were sicker and had more serious injuries, their survival rate was significantly higher.

However, it also leaves us with more work to do. It is a database study, so it’s not possible to go back and find additional information on the study subjects. Knowing selection criteria and operative details would be very helpful. And the overall numbers are low, so more benefits may come to light if we had the statistical power to focus on mortality and ventilator days.

Here are my questions for the authors and presenter:

  1. Have you considered using a larger dataset to get additional information? The mortality and ventilator days in the early vs late subsets were not statistically significant. This might be due to the lack of statistical power from the small number of patients.
  2. Can you speculate on the financial impact of using expanding the use of rib fixation in the elderly? The clinical impact is clear. It looks like the cost savings to the hospital from the reduced ICU and hospital length of stay alone would far offset the cost of performing the procedure, especially if done early.
  3. What selection criteria should be used for choosing the right patients for the procedure? This is probably outside the scope of the study, but it would be interesting to hear you speculate.

This is an important paper and I really look forward to hearing the details!

Reference: Rib fixation in geriatric trauma: mortality benefits for the most vulnerable patients. EAST Annual Assembly abstract #3, 2020.

Abstracts

Best Of EAST 2020 #2: Do Platelet Transfusions Fix Sad Platelets?

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The next abstract from EAST tackles the question of how we can treat platelets that don’t work right in trauma patients. The literature on using platelet transfusions in patients who are taking anti-platelet agents is getting fairly clear: they don’t work. But what about for platelets that don’t work right due to traumatic hemorrhage?

The trauma group at Penn attacked this problem by performing a prospective study at their Level I trauma center. They investigated platelet function using thromboelastography (TEG) with platelet mapping on trauma patients admitted to the intensive care unit over a two year period. They analyzed platelet function and counts at 3, 6, 9, 12, and 24 hours after admission. Platelet function in patients given platelets during any of the intervals were compared to those who were not. Outcomes studied were improvement in platelet function and mortality.

Here are the factoids:

  • A total of 93 patients were entered into the study
  • About half (57%) had platelet dysfunction detected by TEG
  • Mortality was not different between the groups
  • Neither platelet count nor function improved with transfusion

The authors concluded that platelet dysfunction is common in these patients and that platelet transfusions do not appear to restore platelet function.

My comment: This abstract is a bit hard to follow. Hopefully the manuscript will have more detailed tables that break down which patients got platelets and at what times. It appears that patients could have gotten platelets at various times (any, all, or none) after admission to the ICU, and that pre- and post-transfusion TEG runs were analyzedfor each. It’s also not clear if every patient with dysfunction got a transfusion.

The most obvious issue here is that the total number of patients is small, and the numbers getting platelets at each time interval is even smaller (10-49). The statistical power of such a study is very low. It’s not surprising that no significant differences could be detected. This means that failing to see significance doesn’t means it’s not necessarily there, just that many more patients are needed. So it’s hard to buy into the assertion that platelet transfusions don’t matter.

Here are my questions/comments for the presenter:

  1. Why didn’t all patients get platelets? From the table, it looks like nearly all patients had significant dysfunction (defined as MAadp < 40mm) until the end of the 24 hour study period. It looks like some selection bias is possible if there was no defined protocol for giving transfusions to those who had an abnormal TEG.
  2. Is your study sufficiently powered to draw the conclusion it did? The number of patients seems small overall, and doing measurements serially every 3 hours would seem to further weaken the statistics. Please comment on your choice of analysis and how likely you are to actually be able to detect significance.
  3. Be sure to clarify the details of when platelets were given and why, how many measurements were taken and when, and exact patient numbers. These are not clear in the abstract due to length limitations.

This paper is very interesting and I look forward to its presentation.

Reference: Platelet infusions do not correct trauma induced platelet dysfunction. EAST Annual Assembly abstract #24, 2020.

Abstracts, Complications

Best Of EAST 2020 #1: Treatment Of Blunt Carotid & Vertebral Injuries

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The 33rd Annual Assembly of the Eastern Association for the Surgery of Trauma starts in just two weeks! As usual, I will select several interesting abstracts from the bunch to review. I’ll go over the findings of the research, critique it, and then provide a series of questions for the presenter to consider. These questions are ones that members of the audience may very well ask (hint, hint).

And FYI, I always send a heads-up to the presenters with a link to the post so they can study up beforehand!

So let’s get started with the first abstract that will be kicking off the meeting on January 15. Blunt cerebral / vertebral artery injury (BCVI) is one of those insidious injuries that trauma professionals don’t always think about. But they do occur in about 1% of major trauma patients. It’s one of those injuries that can’t be ignored because very serious complications may occur if it is not treated appropriately (think stroke).

Unless there are extenuating circumstances like bleeding or pseudoaneurysm, treatment is usually pharmaceutical. There are two camps: antiplatelet drugs vs anticoagulant drugs. But there is very little data to determine which one is better.

This abstract is a retrospective review from the National Readmission Database (NRD). This resource is maintained by the US government and provides information on patient readmissions nationally across all payors as well as the uninsured. They included all patients > 18 years old with a BCVI and minor injuries in other body regions. Patients who suffered a stroke complication during their initial hospital stay were excluded.

Patients were divided into two groups: those taking an antiplatelet agent and those prescribed an anticoagulant. Outcomes of interest were readmission with CVA and death, within six months.

Here are the factoids:

  • 725 patients with BCVI were found during the five year study period
  • Patients were propensity matched for a 1:1 ratio of patients taking antiplatelet vs anticoagulant drugs, leaving 370 patients for analysis
  • There was a lower rate of admission in the anticoagulant patients vs the antiplatelet ones (9% vs 26%)
  • There were fewer deaths within 6 months in the anticoagulated patients (1.3% vs 3.9%)
  • Median time to stroke was 6-9 days and was not significantly different between the two groups

The authors concluded that the overall stroke rate after BCVI is 6%. They also found an association with lower rates of CVA within 6 months of discharge in patients on anticoagulants. They recommend further studies to determine which type of chemoprophylaxis is best.

My comments: This is an interesting paper that addresses a problem that we don’t have good answers for. The study was well constructed and simple to follow. The two areas that I have questions about are data quality and statistical power.

The NRD is a powerful tool for research, but does have some shortcomings. It only contains information on readmissions, and may not contain some patients who had asymptomatic strokes or massively stroked and died at home. Not knowing these numbers injects some bias and could change the numbers and findings of the study.

The other issue has to do with statistical power. The overall eligible patient group (725 patients) was small in the first place. Propensity matching for a 1:1 ratio shrunk it to only 370, or 185 in each treatment group. My armchair power calculations show that this study would only be able to detect a 7x difference in mortality, and not the 3x difference seen. I’m glad the authors didn’t claim a “significant decrease in CVA” in the anticoagulated patients vs the antiplatelet drug patients.

Here are my questions for the authors:

  1. What do you see as drawbacks to data quality in your study due to use of the National Readmissions Database? How do you think that patients not included in it impacted your data?
  2. Is there anything you can do to improve the statistical power of the study to see if the mortality difference is truly different? Even though your statistical analysis shows significance, the number of subjects doesn’t allow you to claim this until the mortality in the antiplatelet group reaches 9%. 

This was a simple yet fascinating study, and is a start toward helping us determine which of the two drug classes is most appropriate for patients with BCVI.

Reference: Treatment of blunt cerebrovascular injuries: anticoagulants or antiplatelets? EAST Annual Assembly abstract #1, 2020.

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