Tag Archives: DVT

General

Does Aspirin Add Anything To DVT Prophylaxis?

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Venous thromboembolism (VTE) is an ongoing problem for trauma professionals. Most trauma programs have settled on their own flavor of screening, prophylaxis, and treatment once the problem actually surfaces in a patient. Most prophylaxis centers around a combination of mechanical (leg squeezers) and chemical (some type of heparin) management.

Aspirin has been used for prophylaxis for elective orthopedic surgery, and occasionally in trauma patients managed by orthopedic surgeons for years. Existing literature supporting this has been sparse and unconvincing. But since VTE involves platelets as part of the process, why not have another look?

A recently published paper from Scripps in San Diego looked tried to gauge the effect of aspirin on trauma patients where taking it before they were injured. Novel idea. Can the findings be useful? The authors performed a retrospective, case-controlled study of patients who developed post-traumatic deep venous thrombosis (DVT). The patients were matched for 7 covariates, and the authors looked at an additional 26 risk factors. Those taking aspirin pre-injury were compared with those who were not.

Here are the factoids:

  • 172 cases were identified over the 5 ½ year study, and 62 (36%) were excluded because a matched control could not be found
  • 7% of the remaining110

    patients were taking aspirin (why?)

  • 13% of controls were taking aspirin
  • 7% were taking warfarin, and 4% were taking clopidogrel
  • The mean age was 52, ISS was 13-14, and hospital stay was 7-10 days (!)
  • Multivariate analysis showed a significant protective effect from DVT with a risk ratio of 0.17 (!!)
  • But this effect was found only when used in conjunction with heparin prophylaxis after admission

Bottom line: Interesting findings. What does it mean? First, this is a very small retrospective study. It was conducted over 5+ years, so changes in VTE screening and prophylaxis may have occurred at this hospital. But even so, the finding were compelling. The biggest problem is that we can’t expect people to predict that they will need to start taking aspirin. But the study does raise the interesting question of whether it might be helpful to start taking it as soon as the patient arrives at the hospital. This is one of those thought provoking studies that should prompt someone (hint hint) to design a nice prospective study to see if this ultra-cheap drug might help us bring down our VTE rates even more.

Reference: Aspirin as added prophylaxis for deep vein thrombosis in trauma: A retrospective case-control study. J Trauma 80(4):625-630, 2016.

General

A Scan That Can Find Clots Anywhere In The Body

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Our current technology for identifying venous thromboembolism (VTE) / deep venous thrombosis (DVT) consists of duplex ultrasonography, and sometimes, CT angiography. Both are relatively noninvasive and painless (unlike the old-fashioned venography of days gone by.

Researchers at the Massachusetts General Hospital have been working with different chemical probes that could adhere to clot and allow it to be identified on a PET scan. After experimenting with a number of fibrin-targeting peptides they settled upon one called copper fibrin-binding peptide 8 (Cu-FBP8). It was found to have a high affinity for clot, remain stable, and clear quickly from the animal.

A series of rats were subject to a surgically induced thrombus in the carotid or femoral arteries, or a sham operation. The animals were then imaged by CT/PET scan after injection with the Cu-FBP8 probe. The authors found that the probe worked as expected, identifying clot immediately. They were also able to follow resolution over the days following induction. 

Here is a whole-body fused CT/PET scan of one of the animals with both carotid artery (yellow arrow) and femoral artery (blue arrows) clot.

Bottom line: This is a potentially exciting tool that could make it much easier for us to identify DVT and VTE. It could also help us understand the etiology and incidence of PE as well. But as with all animal studies, it remains to be seen whether this will translate into a useful test for humans. Stay tuned, as it will probably take about 3 years to find out the answer.

Reference: 

Multisite Thrombus Imaging and Fibrin Content Estimation With a Single Whole-Body PET Scan in Rats. Arterioscler, Thromb, Vasc Biol 35(10):2114-2121, 2015.

General

Pulmonary Embolism and DVT in Trauma

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We have long assumed that pulmonary emboli start as clots in the deep veins of the legs (or pelvis), then break off and float into the branches of the pulmonary artery in the lungs. A huge industry has developed around how best to deal with or prevent this problem, including mechanical devices (sequential compression devices), chemical prophylaxis (heparin products), and physical devices (IVC filters).

The really interesting thing is that less than half of patients who are diagnosed with a pulmonary embolism have identifiable clots in their leg veins. In one study, 26 of 200 patients developed DVT and 4 had a PE. However, none of the DVT patients developed an embolism, and none of the embolism patients had a DVT! How can this kind of disparity be explained?

Researchers at the Massachusetts General Hospital retrospectively looked at the correlation between DVT and PE in trauma patients over a 3 year period. DVT was screened for on a weekly basis by duplex venous ultrsonagraphy. PE was diagnoses exclusively using CT scan of the chest, but also included the pelvic and leg veins to look for a source. A total of 247 patients underwent the CT study for PE and were included in the study.

Here are the factoids:

  • Forty six patients had PE (39% central, 61% peripheral pulmonary arterial branches) and 18 had DVT (16 seen on the PE CT and 2 found by duplex)
  • Of the 46 patients with PE, only 15% had DVT
  • All patient groups were similar with respect to injuries, injury severity, sex, anticoagulation and lengths of stay
  • Interestingly, 71% of PE patients with DVT had a central PE, but only 33% of patients without DVT had a central PE.

The authors propose 4 possible explanations for their findings:

  1. The diagnostics tools for detecting DVT are not very good. FALSE: CT evaluation is probably the “gold standard”, since venography has long since been abandoned
  2. Many clots originate in the upper extremities. FALSE: most centers do not detect many DVTs in the arms
  3. Leg clots do not break off to throw a PE, they dislodge cleanly and completely. FALSE: cadaver studies have not shown this to be true
  4. Some clots may form on their own in the pulmonary artery due to endothelial inflammation or other unknown mechanisms. POSSIBLE

An invited critique scrutinizes the study’s use of diagnostics and the lack of hard evidence of clot formation in the lungs.

Bottom line: this is a very intriguing study that questions our assumptions about deep venous thrombosis and pulmonary embolism. More work will be done on this question, and I think the result will be a radical change in our use of anticoagulation and IVC filters over the next 3-5 years.

Reference: Pulmonary embolism and deep venous thrombosis in trauma: are they related? Arch Surg 144(10):928-932, 2009.

Complications

How To Predict Venous Thromboembolism In Pediatric Trauma

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As with adults a decade ago, the incidence of venous thromboembolism (VTE) in children is now on the rise. Whereas adult VTE occurs in more than 20% of adult trauma patients without appropriate prophylaxis, it is only about 1% in kids, but increasing. There was a big push in the early 2000′s to develop screening criteria and appropriate methods to prevent VTE. But since the incidence in children was so low, there was no impetus to do the same for children.

The group at OHSU in Portland worked with a number of other US trauma centers, and created some logistic regression equations based on a large dataset from the NTDB. The authors developed and tested 5 different models, each more complex than the last. They ultimately selected a model that provided the best fit with the fewest number of variables.

The tool consists of a list of risk factors, each with an assigned point value. The total point value is then identified on a chart of the regression equation, which shows the risk of VTE in percent.

Here are the factors:

Note that the highest risk factors are age >= 13, ICU admission, and major surgery.

And here is the regression chart:

Bottom line: This is a nice tool, and it’s time for some clinical validation. So now all we have to do is figure out how much risk is too much, and determine which prophylactic tools to use at what level. The key to making this clinically usable is to have a readily available “VTE Risk Calculator” available at your fingertips to do the grunt work. Hmm, maybe I’ll chat with the authors and help develop one!

Reference: A Clinical Tool for the Prediction of Venous Thromboembolism in Pediatric Trauma Patients. JAMA Surg 151(1):50-57, 2016.

General

EAST 2016: How Long Does VTE Risk Last In TBI?

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Most trauma patients
are considered to be at some risk for deep venous thrombosis (DVT) and/or
venous thromboembolism (VTE) during their hospital stay. Trauma professionals
go to great lengths to screen for, prophylax against, and treat these problems.
One of the tougher questions is, how long do we need to worry about it? For
fractures, we know that the risk can persist for months. But what about head
injury?

A group at Brigham
and Women’s Hospital did a large database study looking at the VTE risk in adults
who sustained significant head injury, with only minor injuries to other body
regions. They tried to tease out the risk factors using multivariate regression
models.

Here are the
factoids:

  • Patients were only included if their AIS Head
    was >3, and all other AIS were <3
  • Of the over 50,000 patients in the study,
    overall incidence of VTE was 1.3% during the hospital stay, and 2.8% overall
    within 1 year     of injury
  • Risk factors for VTE after discharge included
    age > 64 (3x), discharge to a skilled nursing facility (3x), and prolonged
    hospital length of stay     (2x)
image

Incidence of VTE over time

Bottom line: View this paper as a glimpse of a potential unexpected
issue. The risk of VTE persists for quite some time after head injury (and
probably in most other risky injuries like spine and pelvic fractures. The
three risk factors identified seem to identify a group of more seriously
injured patients who do not return to their baseline soon after injury. We may
need to consider a longer period of screening in select patients, but I believe
further work needs to be done to help figure out exactly who they are.

Reference: How long should we fear? Long-term risk of
venous thromboembolism in patients with traumatic brain injury. EAST 2016 Oral
abstract #28.