Tag Archives: Heparin

Abstracts, Pharmacy

Best of AAST #1: Aspirin Vs Low Molecular Weight Heparin For VTE Prophylaxis

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The 82nd Annual Meeting of the American Association for the Surgery of Trauma begins next week. As is my custom, I will be reviewing some of the more interesting (to me) oral presentation abstracts until the last day of the meeting.

When reading abstracts, keep in mind that you are seeing just a snippet of a finished manuscript. The authors are given very little print space to fully describe their research idea, their methods, and their results’ significance. Sometimes, what is seen in the abstract varies significantly from what is actually heard at the meeting. But mercifully, this does not happen often. The abstract is usually an intriguing look at some new and exciting work.

Having said all that, an abstract should not be a reason to change your practice! It is usually early work and needs to be fully vetted at peer review. Even then, it needs to be taken in context with past, similar research before trickling down to patient care.

The first abstract is fascinating. Our orthopedic surgery colleagues have been trying to use aspirin for venous thromboembolism (VTE) prophylaxis for decades. Frequently, they are thwarted by the trauma surgeons, who are thoroughly indoctrinated in the low molecular weight heparin (LMWH) camp.

This work comes from the Shock Trauma Center in Baltimore and is a follow on to a paper published in the New England Journal of Medicine earlier this year. The paper demonstrates that aspirin is not inferior to LMWH when used for VTE prophylaxis of patients. There was no difference in death from all causes, VTE occurrence, wound complications, or bleeding events.

The abstract is a follow-on to that manuscript. The authors performed a secondary analysis of the initial data to see if aspirin provided the same apparent level of protection in patients with high risk for VTE as measured by the Caprini score.

Here are the factoids:

  • A total of 12,211 patients were enrolled in this multi-center, and the same outcomes listed above were monitored for 90 days
  • Of the total group, 3052 were judged to be high risk: 46% had a femur fracture, 42% had a pelvic/acetabular fracture, 48% had a thoracic injury, 39% had a spinal injury, and 35% had a head injury
  • There was no difference in death, deep venous thrombosis, pulmonary embolism, or bleeding in the two groups
  • Patient-reported satisfaction was significantly better by 68% in the aspirin group

The authors concluded that outcomes for aspirin vs. LMWH are similar, even in patients at high risk for VTE.

Bottom line: This is an intriguing abstract, pointing me to the original paper published in NEJM. This multi-center study was performed in conjunction with the research coordinating center at Johns Hopkins, which designs some top-notch research. This study was no exception.

I am fascinated with this work because it shows that our orthopedic colleagues were right! They’ve been trying to get us to use aspirin for a long time. It’s very cheap compared to LMWH, by a ratio of about 50,000:1. 

If you’ve followed me for a long time, you would know I have been skeptical of the VTE prophylaxis establishment. Looking historically at its evolution over the last 40+ years, the incidence of DVT and fatal PE have changed very little despite the introduction of heparin, low molecular weight heparin, and anti Factor Xa monitoring. But it’s been established practice, so we’ve had to abide by the rules. Now, a cheaper alternative to all of this is being shown to be just as (in)effective. 

I suspect that if others bear out this work, we will be able to use a cheaper prophylaxis drug that does not require injection. But we still need to work on figuring out the basis for this problem to hopefully reduce it to near zero someday.

References: 

  • Risk-stratified thromboprophylaxis effects of aspirin versus low-molecular-weight heparin in orthopaedic trauma patients. AAST 2023 Plenary Paper 3.
  • Aspirin or Low-Molecular-Weight Heparin for Thromboprophylaxis after a Fracture. N Engl J Med 2023; 388:203-213.
Pharmacy

How Early Can We Start Chemoprophylaxis In TBI Patients?

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We’ve learned a couple of things in the last two posts by reviewing recent systematic review / meta-analysis studies. First, low molecular weight heparin provides better prophylaxis against venous thromboembolism (VTE) than unfractionated heparin. And giving prophylaxis within the first 72 hours of admission significantly decreases the incidence of VTE with no increase in existing intracranial bleeds or mortality.

So the only remaining question is, how low can you go? That is, how soon can you safely start chemoprophylaxis? The trauma group at George Washington University in DC put together a study to examine this question.

They, and one other Level I trauma center, performed a retrospective cohort study of adult, blunt TBI patients over a three year period. Patients with penetrating brain injury, and those with any other body region with significant injury (AIS >1) were excluded so this group truly represented isolated brain injury. Other exclusion criteria were progression of blood on CT within 6 hours, and crani or death within 24 hours. Early VTE prophylaxis was defined as occurring within 24 hours, and late was > 24 hours.

All patients had hourly neuro evaluations and a repeat head CT at six hours after admission. All had compression devices applied to their legs, and received either low molecular weight (LMWH) or unfractionated heparin (UH) at a fixed dose regarding of body habitus. Anti-Factor Xa levels were not measured.

Here are the factoids:

  • Between the two centers, 264 met inclusion criteria
  • About 40% received early prophylaxis and the remaining ones received their drug after 24 hours
  • ISS was higher (18 vs 15) and GCS was lower (13 vs 14) in the late therapy group
  • About 88% of patients in the early prophylaxis group received LMWH vs only 63% in the late group
  • Average time to prophylaxis start in the early group was 17 hours vs 47 hours in the late group
  • There were no differences in bleed progression between early and late groups (5.6% vs 7%)
  • The craniotomy / craniectomy rates were the same in early and late groups (1.9% vs 2.5%)
  • VTE rate was the same in early vs late groups (0% vs 2.5%)

Bottom line: The authors concluded that there was no additional risk in giving early VTE prophylaxis in TBI patients with a stable CT seven hours after arrival. This was true for patients with subdural, epidural, subarachnoid, and intraparenchymal bleeds.

But there are some limitations to consider. This was a retrospective study, and was a “how we do it” study” as well in terms of the choice of LMWH vs UH. This means there was not protocol for the form of heparin used; that was determined by surgeon preference. 

There was also a difference in ISS and GCS between groups. However, the difference may not have been clinically significant, and it could have made the late group look worse if it were. Statistically, it did not.

And finally, the numbers are small and there was no power analysis. So there is the question of whether a significant difference could have even been detected.

What does it all mean? Well, it suggests that early (within 24 hours) chemoprophylaxis does not cause harm compared to later administration. But the study is not definitive enough to change practice yet. It should definitely prompt discussions and practice guideline development for starting prophylaxis after 24 hours of CT scan stability now. And hopefully these authors (or others) are planning a better prospective study to help us start even sooner!

Reference: Early chemoprophylaxis against venous thromboembolism in patients with traumatic brain injury. Am Surgeon 88(2):187-193, 2021.

Pharmacy

Unfractionated vs Low Molecular Weight Heparin For Trauma Patients

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In my last post, I described some of the telltale signs that could be seen in a trauma center’s TQIP report that might suggest there are issues with how they go about providing prophylaxis for venous thromboembolism for their patients. Today, I will analyze a systematic review and meta-analysis of a collection of research that compared the efficacy and safety of unfractionated heparin (UFH) to low molecular weight heparin (LMWH) specifically for trauma patients.

First, it’s important to understand the concept of research quality. There is a huge amount of research published these days, and it varies considerably in how well it is designed, executed, and analyzed. Here is a diagram that illustrates the levels of quality and the volume of research published at each level. By quality, I mean the applicability to clinical treatment of actual humans. For this reason, test tube and animal research are low on the pyramid.

The research that most people consider to be the “gold standard” (randomized, controlled, double blind) is very close to the top. There is one class that, if conducted properly, may even be better. That is the systematic review and meta-analysis.

Most people have heard of meta-analysis, and it can be very good by itself. This combines lots of smaller studies into one larger one. However, it may hampered by the quality of the studies included in the meta-analysis. The tenet of “garbage in equals garbage out” certainly holds. But a systematic review takes that one step further.

The systematic review compiles all possible studies related to a small set of research questions, and usually concentrates on the ones with the highest quality research design. The quality of each of the studies is evaluated, and a meta-analysis is then performed on the best. Results are usually represented in a forest plot. This is an easy way to illustrate the estimated results from a number of studies that address the same question. There is also an entry that shows the relative strength of all of the studies combined. Here’s an example:

There are seven studies included, and each is displayed with its risk ratio (RR) and confidence interval (CI). The final diamond is the combined RR and CI for the entire group of studies. In the example above, note that most of the studies have CI bars that extend over the risk ratio = 1 line, meaning they may not be significant. But when taken together, the final risk ratio of the group is well under 1.0 and does not cross over it, denoting significance.

Let’s now apply this concept to a group of studies comparing UFH and LMWH for prevention of VTE for trauma patients. Based on keyword search, the authors identified 1,227 records for screening. Of those, only 40 were tentativley found to directly address the question. After in-depth analysis, only 12 were eligible for final review. For various reasons, only about 1 in 100 papers could be used to try to analyze the question. This always shocks me.

Here are the efficacy results. All are statistically significant, and all but mortality were stated with moderate certainty. The mortality number had low certainty due to the fact there were only three studies and confidence intervals were very wide.

  • Deep venous thrombosis: LMWH reduced by about 35% compared to UH
  • Pulmonary embolism: LMWH reduced by 44% although certainty was low
  • Any VTE: LMWH reduced by about 30%
  • Mortality: LMWH reduced by 56% (low to very low certainty)

Safety was also analyzed, including bleeding events, unexpected return to OR, heparin induced thrombocytopenia (HIT), and “any adverse events.” All of the Total Confidence Interval diamonds were situated on the risk ratio = 1 line, denoting no significant change when comparing LMWH vs UH.  However, quality of this data was noted to be low due to the quality of the individual studies. This means that we do not really know the answer to the safety question with any certainty yet.

Bottom line: This is one of the best summaries of our research on UH vs LMHW to date. It broadly reviewed the available literature and found only a small subset to analyze. It is clear that LMWH is superior for prevention of DVT and VTE overall. However, the impact on pulmonary embolism and death is still unclear.

As far as safety, the studies are still of quality that is too low to use for a decent analysis. Although this study did not detect any increase in complications, we still can’t say with any degree of certainty.

So what does it all mean? We have been using LMWH for decades now. Most likely, if there were regular complications like bleeding, unexpected return to OR, or HIT we would have definitely noticed it by now. Fortunately, we only have a few anecdotes and case reports to scare us off.

Overall, there is good support for the use of LMWH exclusively in most trauma patients. However, the prescribing provider should always assess patient factors that may suggest that UH might be better is a specific case. But remember that using UH trades an unclear/unlikely safety advantage for a recognized decrease in efficacy.

Reference: Efficacy and safety of low molecular weight heparin versus unfractionated heparin for prevention of venous thromboembolism in trauma patients. Ann Surgery 275(1):19-28, 2022.

Pharmacy

VTE Prophylaxis And TBI

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There has been a tremendous amount of gnashing of teeth regarding venous thromboembolism (VTE) prophylaxis in patients with blood in their head. This means any kind of blood: subarachnoid / epidural / subdural hematomas as well as intraparenchymal hemorrhage.

Trauma professionals have traditionally been hesitant to give any type of anticoagulant to a patient who has just bled, or who may be at risk for bleeding in the very near future. This becomes even more important in areas like the brain where management is a bit more difficult and adverse events can be devastating.

For this reason, our neurosurgical colleagues frequently like to steer the ship and dictate what type of VTE prophylaxis can be given, and when. Unfortunately, much of their advice may be driven by dogma and what they learned about the subject during their training. Having studied hundreds of TQIP reports over the past few years, I’ve learned to pick out hospitals that are relying on the advice of non-trauma surgeons to direct the prophylactic regimen.

Here are two dead giveaways that something is amiss. First, look at your TQIP report table titled “Pharmacologic VTE Prophylaxis Type.”

Compare the use of unfractionated heparin vs low molecular weight heparin (LMWH). This hospital has a huge variance from the norm compared to other comparable trauma centers. This means that “someone” is dictating its use for some subset of patients.

In my experience, this is typically a neurotrauma thing. Now take a look at the TQIP table titled “Pharmacologic VTE Prophylaxis.” Specifically, look at the “Severe TBI” cohort for time to VTE prophylaxis.

It is very clear that there is a significant delay to administering VTE prophylaxis to TBI patients. These two data points indicate that there is some reluctance to giving appropriate treatment to these patients.

The literature is clear that VTE prophylaxis is important in many trauma patients, including those with serious head injury. There are three questions that need to be answered to settle on optimal care:

  1. Which chemoprophylaxis is best, unfractionated or low molecular weight heparin?
  2. Is it better to give the selected agent earlier or later?
  3. If earlier is better, how early can we give it?

I will address each of these questions in this series of posts, focusing on neurotrauma patients. In order to try to toss out dogma, the literature I cite will be recent, no more than about two years old. So join me for battle next week as we have unfractionated vs low molecular weight heparin face off.

Thanks to Jim Sargent from Beth Israel Deaconess Medical Center for suggesting this topic.

Complications, General, Pharmacy

Aspirin For DVT Prophylaxis In Trauma

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The use of mechanical and pharmacologic prophylaxis for prevention of deep venous thrombosis (DVT) and venous thromboembolism (VTE) in trauma patients is nearly universal. However, no matter how closely we adhere to existing guidelines, some patients will develop these conditions. Indeed, about 80% of patient who suffer some type of VTE event were receiving prophylaxis at the time.

Trauma is a major factor in causing hypercoagulability. Although current chemoprophylaxis focuses on clotting factors, platelets play a big part in the clot formation process. Our usual drugs, though (various flavors of heparin), have no effect on them.

What about adding aspirin to the regimen? My orthopedic colleagues have been requesting this for years. There is a reasonable amount of data in their literature that it is effect in patients with knee arthroplasty only. As usual, it is misguided to try to generalize management based on experience from one specific body region or operation.

A single Level I trauma center reviewed its data on aspirin prophylaxis for trauma patients. They reviewed their registry data from 2006 to 2011. They identified 172 trauma patients with duplex ultrasound proven DVT. These patients were matched with 1,901 control patients who underwent at least one duplex and never developed DVT. Matching was performed carefully to ensure that age, probability of death, number of DVT risk factors, and presence of TBI were similar. The total number of matched patients studied was 110.

And here are the factoids:

  • About 7% of patients with DVT were on aspirin at the time of their injury, vs 14% of the matched controls
  • 7% were taking warfarin, and 4% were taking clopidogrel
  • Analysis showed that patients taking aspirin had a significantly decreased chance of DVT after injury
  • On further analysis, it was found that this effect was only significant if some form of heparin was given for prophylaxis as well.

Bottom line: So before you run off and start giving your patients aspirin, think about what this study really said. Patients taking aspirin before their injury and coupled with heparin after their injury have a lower rate of DVT. It gives us no guidance as to whether adding aspirin after the fact, or using aspirin alone, are useful.  And we still don’t know if any of this decreases pulmonary embolism or mortality rates.

Related posts:

Reference: Aspirin as added prophylaxis for deep vein thrombosis in trauma: a retrospective case-control study. J Trauma 80(4):625-30, 2016.