Tag Archives: DVT

Routine Duplex Screening For Venous Thromboembolism

Venous thromboembolism (VTE) is a potential problem for all hospitalized patients, and traumatic injury is yet an additional risk factor for its occurrence. Most trauma centers have some kind of risk assessment tool to help the tailor their chemoprophylaxis regimen to patients most at risk. But far fewer have adopted the use of screening ultrasounds to monitor for new onset VTE that would dictate conversion to therapeutic treatment.

Unfortunately, in the US, the Centers for Medicare and Medicaid Services (CMS) has deemed VTE as a “never” event and penalizes hospitals when they report it. One of the unintentional consequences of this (or is it?) is that hospitals may then pressure trauma programs to avoid surveillance in order to “make the numbers look better.” Remember Law X from Samuel Shem’s House of God?

X. If you don’t take a temperature, you can’t find a fever.

Similarly, if you don’t do a duplex screen, you probably won’t detect VTE. Now granted. some patients develop classic symptoms like edema, pain, and tenderness. But not that many.

But is this wise? My contention has been that if the patient doesn’t develop symptoms that catch your attention, yet they develop VTE that you don’t know about, they are at risk for more serious complications like pulmonary embolism (PE). And you are blithely unaware.

The trauma group at Intermountain Medical Center in Salt Lake City performed an elegant study to determine the impact of screening for VTE in their trauma patients. They performed a prospective, randomized trial on trauma patients admitted over a 30-month period. Patients were included if they were judged to be at moderate to high risk based on their risk assessment profile (RAP) score. Patients were excluded if they were children, had VTE or PE within 6 months prior to hospitalization, or had some type of hypercoagulable state.

Patients were sequentially randomized to no duplex screening vs screening on days 1, 3, 7, and then weekly thereafter. The primary outcome measure was PE during the hospital stay. Secondary outcomes consisted of a number of factors relating to development of DVT.

Here are the factoids:

  • Nearly two thousand patients were enrolled, with about 995 patients in each group and no differences in demographics
  • The ultrasound group had significantly more below-knee (124 vs 8) and above knee (19 vs 8) DVT identified (no surprise there)
  • The ultrasound group had significantly fewer pulmonary emboli than the no ultrasound group (1 vs 9) (lots of surprise here!)
  • Mortality was similar during the hospital stay and for 90 days after

Bottom line: If you look for it, you will find it! This is the definition of surveillance bias. But in in this study, looking for clots in the legs may also decrease the number of patients who develop symptomatic pulmonary embolism. How could this be?

There are a few possibilities. The majority of DVT found in the surveillance group were located distally. Although there is some uncertainty as to how likely these are to embolize, it is probably very low. So let’s ignore them for now and assume that only the proximal clots might embolize.

This leaves an extra 11 DVT found in the surveillance group over and above the no-ultrasound group. Despite that, the surveillance group had only one PE vs 9 in the no-ultrasound group!

Another explanation was that the ultrasound guided changes in management, shifting to management to therapeutic drug dosing. The authors did not find a significant difference between the use of therapeutic vs prophylactic dosing between the groups. But there was a difference. Although the overall study was well-powered, there really weren’t enough numbers to show whether there was a true difference in therapeutic dosing. Fourteen patients in the ultrasound group got therapeutic anticoagulation compared to only 4 in the no-surveillance group. I think this is the actual reason.

Overall, this is a well-designed and well-executed study that shows why taking the Ron Popeil approach to DVT prophylaxis (“set it and forget it”) doesn’t work. Patients do occasionally develop proximal DVT on standard chemoprophylaxis (and frequently develop distal DVT), but it doesn’t always result in obvious signs and symptoms. This study shows that if you don’t look for it, you may not know until they suddenly develop chest pain, air hunger, and worse! So consider carefully if your practice guideline doesn’t yet include surveillance.

Reference: Trauma Patients at Risk for Venous Thromboembolism who Undergo Routine Duplex Ultrasound Screening Experience Fewer Pulmonary Emboli: A Prospective Randomized Trial. J Trauma, publish ahead of print, Publish Ahead of Print. DOI: 10.1097/TA.0000000000003104, February 4, 2021.

Should I Apply Compression Devices To Patients With DVT?

Everyone knows that venous thromboembolism (VTE) is a potential problem in hospitalized patients, and especially so in trauma patients. Several groups of them are at higher risk by virtue of the particular injuries they have sustained and the activity restriction caused.

Nearly every trauma program uses some form of screening and prophylaxis in an attempt to reduce the occurrence of this problem, which can result in deep venous thrombosis (DVT) and/or pulmonary embolism (PE). Screening looks at patient factors such as age, obesity, previous VTE as well as injury risk factors like spine and pelvic fractures, and decreased mobility.

Based on the screening protocol, prophylaxis may be prescribed depending upon level of VTE risk, which is then balanced with bleeding risk from brain, solid organ, or other injuries. The choices we have are primarily mechanical vs chemical and consist of compression devices (sequential or not) and various heparins.

An age old question surfaced on my own patient rounds recently. If a patient breaks through their prophylaxis and develops DVT, is it safe to apply compression devices to the extremity?

There has always been the fear that doing things that increase flow in the affected extremity may cause clots to dislodge and ultimately cause a PE. Seems logical right? But we know that often, our common sense about things is completely wrong.  Couldn’t just moving around cause pieces to break off? A meta-analysis of 13 studies published in 2015 showed that early ambulation was not associated with a higher incidence of new PE. Furthermore, patients who suffered from pain in the affected extremity noted significant improvements with early ambulation.

If ambulation makes the pain better, could the veins be recanalizing more quickly? Another study examined a small group of 72 people with DVT receiving anticoagulants, half of whom were prescribed exercise and compression stockings and the other half stockings only. There was a huge amount of variability in the rates of recanalization, but ultimately there were no significant differences with or without exercise.

So just lying in bed is not good, and exercise/ambulation may actually make people feel better. But interestingly, bedrest alone does not appear to increase the likelihood of PE! It does decrease the risk of developing problems other than the VTE, like pulmonary complications.

But what about compression devices? Common sense would say that you are intermittently  increasing pressures in the leg veins, which could dislodge any loose clots and send them flying to the lungs, right?

Unfortunately, I couldn’t find a paper from anyone who had the courage to try this. Or perhaps no institutional review board (IRB) would approve it. But the key fact is that every compression device manufacturer includes existing DVT as a contraindication in their product documentation. They don’t have any literature either, so I assume it’s an attempt to limit litigation, just in case.

Bottom line: Walking provides at least as much muscle compression as compression devices. But the simple truth is that we have no solid research that either supports or condemns the use of active compression devices in patients with known DVT. And we probably won’t, ever.

Compression stockings seem to be safe, but they really don’t do much. They are white, but don’t do much more than contribute to hospital clothing fashion. Since the manufacturers define existing DVT as a contraindication, application of their product would be considered an off-label use. So it looks like we cannot in good faith use these devices in patients with diagnosed DVT.

References:

  • Bed Rest versus Early Ambulation with Standard Anticoagulation in The Management of Deep Vein Thrombosis: A Meta-Analysis. PLOS One , April 10, 2015, https://doi.org/10.1371/journal.pone.0121388
  • Bed Rest or Ambulation in the Initial Treatment of Patients With Acute Deep Vein Thrombosis or Pulmonary Embolism: Findings From the RIETE Registry. Chest 127(5):1631-1636, 2005.
  • Does supervised exercise after deep venous thrombosis improve recanalization of occluded vein segments? A randomized study. J Thrombosis Thrombolysis 23:25-30, 2006.

Best Of AAST #8: Duplex Screening For DVT

To screen on not to screen, that is the question. If you do more testing, you will find more cases. But does it make a difference clinically? Sounds like some of the questions coming up in our current discussion of the Coronavirus. But that’s what we really need to know.

The group at Intermountain Medical Center in Salt Lake City performed a 2 ½ year randomized, prospective study of screening duplex ultrasound of the lower extremities vs no screening study. They used the Risk Assessment Profile (RAP) developed by Greenfield, first published in 2000. Any patient at moderate or higher risk for DVT (RAP score >5) was enrolled in the study. They were randomized into two groups: a screening group who received duplex scans on days 1, 3, 7, and then weekly, and a “no routine screening” group. All patients received chemoprophylaxis per the trauma service’s existing protocol.

The RAP score is a 17 factor scale that assigns a specific number of points based on underlying medical conditions, iatrogenic factors like central lines or transfusions, injury-related factors, and age.

Here are the factoids:

  • A total of 3,236 trauma patients were identified, and the 1,989 who were at moderate or higher risk for DVT were evenly randomized to screening vs no screening
  • There were no differences in age, sex, BMI, mechanism, ISS, or length of stay between the two groups
  • The incidence of DVT was 15% in the screened group vs 1.7% in the no screening group

The authors concluded that screening diagnoses more DVT, most of which is below the knee. And they also noted that screening identified DVT more often than clinical exam alone, but does not result in fewer PE or deaths. They suggest that more work needs to be done to identify exactly who benefits from duplex screening the most.

Here are my comments:

Finally, an easy to follow and well-designed study! But I think some of the results may be missing from the abstract. That section cuts off in the middle of some of the statistics, and there is no mention of the clot location or PE/mortality rates mentioned in the conclusion.

I also worry that a thousand patients in each group may not be enough. We are working with low incidence end points like PE and death, and this is an association study with many potential confounders/factors that may not have been recorded. I generally like to see the ability to detect a minimum of a 2x effect. So if the incidence of PE is 1.5%, I like to see the ability to detect a difference if the other group is 3%.

And speaking of study size. The RAP score was first described in 1997 and was a pilot study. They drew their conclusions from only 53 patients, and the only risk factor that they could show that was a statistically significant predictor of DVT was age. They concluded that surveillance of patients with RAP > 5 was warranted. This abstract builds upon this work, but is trying to say that maybe we don’t need to do duplex scans.

Here are my questions for the presenter and authors:

  • Is there some text missing from the end of the results section of the abstract? It seems to end unexpectedly, and some things are mentioned in the conclusions that are not in the results.
  • Why did you choose the RAP score? There are other risk assessment tools available out there. What is so special about RAP?
  • Is your sample size large enough to detect differences in incidence of PE or death? My back of the envelope calculations suggest at least 1,500 patients would be needed in each group.
  • How long did you follow patients to determine if they had PE or death? Until they were discharged? Later than that?  This makes a big difference in the eventual incidence of these outcomes.
  • Based on what you found, is there any value to treating asymptomatic proximal DVT? It sounds like you are saying that screening is not needed at all because PE and death are the same. Isn’t there value in treating proximal DVT if you find it?

This abstract certainly got me thinking! I am looking forward to the presentation and discussion of this abstract!

Reference: Head in the sand? The value of routine duplex ultrasound screening for venous thromboembolism in the trauma patient: a randomized Vanguard trial. AAST 2020, Oral Abstract #16.

How To Predict Venous Thromboembolism In Pediatric Trauma

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.

The IVC Filter In Trauma: Why?

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 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.

Tomorrow: a look at trends in filter insertion and retrieval.

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.