Monthly Archives: January 2020

Abstracts, Prevention

Best Of EAST #6: Uber / Lyft vs Drunk Driving

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Ride share services like Uber and Lyft are now pretty much ubiquitous. It’s so easy to get a ride these days one would think that the incidence of car crashes due to drunk driving should be declining, right?

Well, nobody knows for sure. But the group at Tulane decided to look at their own data for alcohol-related car crashes over a seven year period. They also combed regional traffic databases for more information and compared the data from pre- to post- arrival of ride share services.

Here are the factoids:

  • There were 1474 patients involved in alcohol-related crashes (ARC)
  • The proportion of alcohol-related ARCs decreased significantly from 39% to 29%
  • The overall annual incidence of fatal ARCs seen at Tulane decreased significantly from 11.6 to 5, and also decreased significantly within the region
  • However, the incidence of ARCs only decreased within the 21-24 year age group(!)

My comment: This is very interesting work! The statistics appear to be sound and the number sufficiently large. It shows that it might be possible to decrease drunk driving injuries using methods other that the usual prevention efforts. It is puzzling, though, that the effect is only seen in a very narrow age group in the population. Practically everyone can use a ride-hailing app these days. Even I do!

Here are my questions for the authors and presenter:

  1. How do you explain the very narrow age-range that appears to be affected? Remember, this study shows an association, not cause and effect. Could it be that something else is reducing alcohol-related crashes in this specific age group, and it has nothing to do with ride share availability? What else could it be?
  2. How can this decrease in 21-24 year olds hold when there was such a significant decrease in overall alcohol-related crashes? Was everyone driving around New Orleans in that age group? Otherwise, how can this be explained?

I am fascinated by this study. But it’s going to be difficult to separate out other confounding variables and causes to be able to point definitively to any benefit from ride share services.

Reference: Do ride sharing services affect the incidence of alcohol-related motor vehicle collisions? EAST Annual Assembly abstract #22, 2020.

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.