Tag Archives: pulmonary embolism

Equipment

The IVC Filter In Trauma: Why?

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The inferior vena cava (IVC) filter has been around in one form or another for over 40 years. One would think that we would have figured everything about it out by now. But no!  The filter has evolved through a number of iterations and form factors over the years. The existing studies, in general, give us piecemeal information on the utility and safety of the device.

One of the major innovations with this technology came with the development of a removable filter. Take a look at the product below. Note the hook at the top and the (relatively) blunt tips of the feet. This allows a metal sheath to be slipped over the filter while in place in the IVC. The legs collapse, and the entire thing can be removed via the internal jugular vein.

ivc-filter-complications1

The availability of the removable filter led the American College of Chest Physicians to recommend their placement in patients with known pulmonary embolism (PE) or proximal deep venous thrombosis (DVT) in patients with contraindications to anticoagulation. Unfortunately, this has been generalized by some trauma professionals over the years to include any trauma patients at high risk for DVT or PE, but who don’t actually have them yet.

One would think that, given the appearance of one of these filters, they would be protective and clots would get caught up in the legs and be unable to travel to the lungs as a PE. Previous studies have taught us that this is not necessarily the case. Plus, the filter can’t stop clots that originate in the upper extremities from becoming an embolism. And there are quite a few papers that have demonstrated the short- and long-term complications, including clot at and below the filter as well as post-phlebitic syndrome in the lower extremities.

A new study from Boston University reviewed their own experience retrospectively over a 9 year period. This cohort study looked at patients with and without filters, matching them for age, sex, race, and injury severity. The authors specifically looked at mortality, and used four study periods during the 9 year interval.

Here are the factoids:

  • Over 18,000 patients were admitted during the study period, resulting in 451 with an IVC filter inserted and 1343 matched controls
  • The patients were followed for an average of 4 years after hospitalization
  • Mortality was identical between patients with filters vs the matched controls

dvt-study

  • There was still no difference in mortality, even if the patients with the filter had DVT or PE present when it was inserted
  • Only 8% ever had their “removable” filter removed (!)

Bottom line: Hopefully, it’s becoming obvious to all that the era of the IVC filter has come and gone. There are many studies that show the downside of placement. And there are several (including this one) that show how forgetful we are about taking them out when no longer needed. And, of course, they are expensive. But the final straw is that they do not seem to protect our patients like we thought (hoped?) they would. It’s time to reconsider those DVT/PE protocols and think really hard about whether we should be inserting IVC filters in trauma patients at all.

Related post:

Reference: Association Between Inferior Vena Cava Filter Insertion
in Trauma Patients and In-Hospital and Overall Mortality. JAMA Surg, online ahead of print, September 28, 2016.

Complications

Predicting VTE Risk In Children

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There’s a lot of debate about if and at what age injured children develop significant risk for venous thromboembolism (VTE). In the adult world, it’s a little more clear cut, and nearly every patient gets some type of prophylactic device or drug. Kids, we’re not so certain about at all.

The Children’s Hospital of Wisconsin tried to tease out these factors to develop and implement a practice guideline for pediatric VTE prophylaxis. They prospectively reviewed over 4000 pediatric patients admitted over a 6 year period.

It looks like the guideline was developed using some or all of this data, then tested using regression models to determine which factors were significant. The guideline was then tweaked and a final model implemented.

Here are the factoids:

  • 588 of the patients (14%) were admitted to the ICU, and 199 of these were identified as high risk by the guidelines
  • Median age was 10 (this is always important in these studies)
  • VTE occurred in 4% of the ICU patients, and 10% of the high risk ones
  • Significant risk factors included presence of central venous catheter, use of inotropes, immobilization, and GCS < 9

Bottom line: This abstract confuses me. How were the guidelines developed? What were they, exactly? And the results seem to pertain to the ICU patients only. What about the non-ICU kids? The abstract just can’t convey enough information to do the study justice. Hopefully, the oral presentation will explain all.

I prefer a very nice analysis done at the Oregon Health Science University in Portland. I wrote about this study earlier this year. The authors developed a very useful calculator that includes most of the risk factors in this model, and a few more. Input the specific risks, and out comes a nice score. The only issue is, what is the score threshold to begin prophylaxis and monitoring? Much more practical (and understandable) than this abstract. Check it out at the link below.

Related post:

References:

  1. Evaluation of guidelines for injured children at high risk for VTE: a prospective observational study. AAST 2016, Paper 68.
  2. A Clinical Tool for the Prediction of Venous Thromboembolism in Pediatric Trauma Patients. JAMA Surg 151(1):50-57, 2016.
Pharmacy

Battle of the Heparins: Unfractionated vs Low Molecular Weight

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Most trauma programs tend toward using low molecular weight heparin (LMWH) products for VTE prophylaxis over plain, old-fashioned unfractionated heparin (UH). How did this happen? LMWH is more expensive than UH, and there is precious little high quality research supporting it.

But, LMWH is very convenient, as it only needs to be given only once or twice daily via subq injection, whereas UH is given as a continuous infusion or subq three times a day. And a fair amount of lower quality data suggests that it is effective in decreasing deep venous thrombosis (DVT) and pulmonary embolism (PE).

This abstract comes from Sunnybrook in Toronto. The authors used sophisticated statistical models to compare centers that predominantly use LMWH to prevent VTE vs those that use UH.

Here are the factoids:

  • This was a huge data analysis from the ACS Trauma Quality Improvement Program database (~ 110,000 records from 214 trauma centers)
  • LMWH was most commonly used, 74% of the time
  • Patients who were more likely to need rapid reversal were more often given UH (older patients, severe TBI, early intracranial interventions)
  • Pulmonary embolism was significantly lower with LMWH (1.8% vs 2.4%)
  • This significant effect was present across all subgroups, including patients with shock, blunt multisystem injury, penetrating trunk injury, isolated orthopedic injury, and severe TBI
  • Trauma centers that predominantly used LMWH had significantly lower PE rates compared to UH (1.2% vs 1.8%)

Bottom line: Even given the vagaries of using huge, retrospective database reviews, this is pretty good data. The use of LMWH appears to be superior to UH in reducing the incidence of pulmonary embolism. It does not prevent it completely. But it’s a good start.

What the authors do not say, and I am curious about, is the impact on DVT. That is a much more common problem than PE. Was there any difference? Did they run out of room to comment on it in the abstract? I kind of doubt it. The devil will be in the details. Listen in on the presentation at the meeting!

Reference: Efficacy of low molecular weight heparin vs unfractionated heparin to prevent pulmonary embolism following major trauma: results from the American College of Surgeons Trauma Quality Improvement Program. AAST 2016 Paper #5.

General

Where Do Pulmonary Emboli Really Come From?

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For a long time, we “knew” that pulmonary emboli were a possible and dreaded complication of deep venous thrombosis (DVT). However, we are beginning to discover that this is not always the case. The group in San Diego decided to see if there really are two different types of PE in trauma, and what that means.

Here’s another VTE paper from Scripps Mercy Hospital, a level I trauma center in San Diego. It looked at 5 ½ years of their experience with adult trauma patients who were routinely screened for DVT. Any of these patients who developed a PE within 6 weeks of admission were evaluated further.

Here are the factoids:

  • Duplex screening from groin to ankle was carried out twice weekly in ICU patients, and once weekly in ward patients
  • Surveillance was carried out if the patient would be non-ambulatory for more than 72 hours, or were at moderate or higher risk for DVT using the ACCP guidelines
  • Nearly 12,000 patients were evaluated by the trauma service and 2,881 underwent surveillance
  • 31 patients (1%) developed a PE
  • 12 of these 31 had DVT identified before or immediately after their PE. Clot was below-knee in 9 (!), above-knee in 2, and in the IJ in one.
  • 19 patients had PE but no DVT identified (de novo PE, DNPE)
  • DNPE tended to be single and peripherally located, and associated with rib fractures, pulmonary contusions, blood transfusions, and pneumonia
  • DVT + PE were more often found in multiple lobes or bilaterally

Bottom line: Like most, this is not a perfect study, but it’s a really good one. It is looking more and more likely that some PEs arise de novo, without any associated DVT. These clots are more likely to be linked to some type of inflammatory process, and have a tendency toward causing more of the classic signs and symptoms of PE. There are still lots of questions to be answered, like do you need to anticoagulate the de novo PEs? But for now, no change in practice. Just be aware that these might not be as bad as they seem.

Reference: Pulmonary embolism without deep venous thrombosis: de novo or missed deep venous thrombosis? J Trauma 76(5):1270-1281, 2014.

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.