Tag Archives: DVT

Procedures

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 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.

Pharmacy

DVT Prophylaxis At Home: Do Our Patients Do What They Are Told?

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Deep venous thrombosis (DVT) is a big potential problem for many trauma patients, particularly those with orthopedic injuries. Patients at high risk are frequently given a prophylaxis regimen to take home after discharge while they are still at higher risk for clots. The particular choice of medication typically comes down to oral (warfarin or aspirin) vs injectable (low molecular weight heparin (LMWH)).

There is quite a bit of literature on patient compliance with their medication routines, or should I say noncompliance? The group at ShockTrauma in Baltimore evaluated how well orthopedic surgery patients adhered to their prescribed DVT prophylaxis schedule after discharge.

They conducted a randomized, prospective trial on all patients who underwent operative management of extremity or pelvic fractures. These patients were prescribed either oral low dose aspirin (81mg) or subcutaneous injections of LMWH (30mg bid). All completed a standardized 8-question tool to gauge their compliance with the medication regimen. Nicely, a power analysis was performed to identify the minimum number of patients needed to achieve statistical significance ( 126 total patients).

Here are the factoids:

  • Of 1450 potential patients undergoing operative fracture fixation, 329 were eligible for the study. All but 150 were excluded primarily due to no need for prophylaxis or inability to contact.
  • Overall adherence to the prophylaxis plan was fairly high, with 65% of patients having high adherence, 21% medium, and 20% low.
  • A quarter of the LMWH patients felt “hassled” by their regimen, while only 9% of the aspirin group did
  • LMWH prophylaxis was associated with low or medium adherence
  • Having to self-administer the prophylactic agent, being a male, and young was also associated with lower compliance

Bottom line: Interesting study. And unfortunately it suggests that our patients don’t always do what they are told, especially if they have to stick themselves with needles. So they may not be getting the prophylaxis we think they are. Furthermore, we’re not even sure if aspirin (or LMWH for that matter) make a difference in the incidence of death or major pulmonary embolism in these patients.

There are a lot of opportunities for mayhem in this study. A third of the enrolled patients were not even compliant with completing the survey. This is certainly a source of bias, and most likely suggests that the overall compliance rates would have been even lower if they had. 

Keep in mind the risk factors for compliance (age, sex, drug route) when deciding how and what to provide for DVT prophylaxis. Your patient may not be doing what you assume they are!

General

VTE Prophylaxis Before Spine Surgery?

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Many surgeons and surgical subspecialists are nervous about operating on people who are taking anticoagulants. This seems obvious when it involves patients on therapeutic anticoagulation. But it is much less clear when we are talking about lower prophylactic doses.

Spine surgeons are especially reluctant when they are operating around the spinal cord. Yet patients with spine injury are generally at the highest risk for developing venous thromboembolic (VTE) complications like deep venous thrombosis (DVT) or pulmonary embolism (PE). Is this concern warranted?

Surgeons at the Presley Trauma Center in Memphis examined this issue by performing a retrospective review of six years worth of patients who underwent spine stabilization surgery. They specifically looked at administration of any kind of preop prophylactic anticoagulant, and the most feared complications of bleeding complications and postop VTE.

Here are the factoids:

  • A total of 705 patients were reviewed, with roughly half receiving at least one preop prophylactic dose and the other half receiving none
  • There were 447 C-spine, 231 T-spine, and 132 L-spine operations, performed an average of 4 days after admission
  • Overall, bleeding complications occurred in 2.6% and VTE in 2.8%
  • Patients with VTE were more severely injured (ISS 27 vs 18)
  • Those who received at least half of their possible prophylactic doses had a significantly lower PE rate (0.4% vs 2.2%) but no significant difference in DVT or bleeding complications

Bottom line: So what to make of this? It’s a relatively small, retrospective study, and there is no power analysis. Furthermore, this hospital does not perform routine DVT screening, so that component of VTE may be underestimated, rendering the conclusions invalid.

However, the information on bleeding complications is more interesting, since this is much more reliably diagnosed using an eyeball check under the dressing. So maybe we (meaning our neurosurgeons and orthopedic spine surgeons) need to worry less about preop prophylactic VTE drugs. But we still need better research about whether any of this actually makes a dent in VTE and mortality from PE. To be continued.

Reference: Early chemoprophylaxis is associated with decreased venous thromboembolism risk without concomitant increase in intraspinal hematoma expansion after traumatic spinal cord injury. J Trauma 83(6):1108-1113, 2017.

Pharmacy

ACS Trauma Abstracts #4: Timing Of DVT Prophylaxis In Spine Trauma

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Spine trauma is one of the high-risk indicators for deep venous thrombosis (DVT). Unfortunately, there is a great deal of variability in the start time for chemical prophylaxis for this injury, especially after the patient has undergone surgery. In part, this is due to a lack of good literature and guidelines, and in part due to the preferences of the spine surgeons who operate  on these patients.

A group at the University of Arizona in Tucson performed a large database review (looks like National Trauma Databank, although they don’t say in the abstract) looking at “early” vs “late” administration of prophylaxis after surgery in these patients. The spine injury was the predominant one, with all other systems having an abbreviated injury score (AIS) < 3. They matched two years worth of patients for demographics, initial vitals, type of operative intervention, and type of heparin to assess the impact of prophylaxis timing.

Here are the factoids:

  • Nearly 40,000 patient records were reviewed, and over 9,500 met the spine injury criteria with operation and prophylaxis. A total of 3,556 could be matched for analysis.
  • These patients were split in half for matching, late (>48 hrs) versus early (<48 hrs)
  • DVT rate was significantly lowe in the early prophylaxis group (2% vs 11%)
  • PE rate and mortality were the same between groups
  • Return to OR and blood transfusion rates were identical (1% and 1-2 units)

Bottom line: Once again, we see that “early” prophylaxis for DVT is probably desirable and mostly harmless, even after a spine operation. Many surgeons still have an irrational fear of giving heparin products in patients who have some risk of bleeding. The body of literature that supports early use just keeps growing. One observation, though: as in most other studies, pretty much whatever we do for DVT has a negligible impact on PE and mortality. We can only treat the clots, but not their major aftermath.

Reference:  Optimal timing of initiation of thromboprophylaxis in spinal trauma after operative intervention: – propensity-matched analysis. JACS 225(4S1):S59-S69, 2017.

Pharmacy

Is Fine-Tuning Lovenox Dosage Using Anti-Factor Xa Worthwhile?

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Deep venous thrombosis (DVT) and pulmonary embolism (PE), collectively known as venous thromboembolism (VTE), are major concerns in all hospitalized patients. A whole infrastructure has been developed to stratify risk, monitor for the presence of, and provide prophylactic and/or therapeutic drugs for treatment. But if you critically look at the literature from the past 20 years or so, we have not made much progress.

One of the newer additions to our arsenal has been to figure a way to determine the “optimal” dose of enoxaparin. Three options are now available: weight-based dosing, confirmation by thormboelastography (TEG), and anti-factor Xa assay. Let’s look at another paper that focuses on the last item.

Anti-factor Xa levels provide a way to monitor low molecular weight heparin activity. A number of papers published have sought to determine a level that predicts adequate activity. Although they are not of the greatest size or quality, a range of 0.2-0.4 IU/ml seems to be the consensus.

A large number of patients at a busy Level I trauma center were retrospectively studied to see if achieving a peak anti-factor Xa level of at least 0.2 IU/ml would result in less VTE. All patients were started on enoxaparin 30mg SQ bid within 48 hours of admission. Anti-factor Xa was measured 4 hours after the third dose. If the level was less than 0.2 IU/ml, the dose was increased by 10mg per dose. The cycle was repeated until anti-factor Xa was therapeutic.

Here are the factoids:

  •  All patients with a Greenfield Risk Assessment Profile (RAP) of 10 or more (high risk) were included; duplex ultrasound surveillance for lower extremity DVT was performed weekly
  • 194 patients were included, with an average RAP of 9 and ISS of 23 (hurt!)
  • Overall VTE rate was 7.4%, with 10 DVT and 5 PE (!)
  • Median time to diagnosis was 14 days
  • Initial anti-factor Xa levels were therapeutic in only one third of patients, and another 20% reached it after dose increases. 47% never achieved the desired level, even on 60mg bid dosing.
  • There was no difference in DVT, PE, or VTE rates in patients who did vs did not achieve the goal anti-factor Xa level
  • Injury severity and obesity correlated with inability to reach the desired anti-factor Xa level

Bottom line: In this study, achieving or not achieving the goal anti-factor Xa level made no difference whether the patient developed VTE or not. And it was difficult to achieve anyway; only about half ever made it to the desired level. How can this happen?

Well, there are still many things we don’t understand about the genesis of VTE. There are probably genetic factors in every patient that modify their propensity to develop it after trauma. And there are certainly additional mechanisms at play which we do not yet understand. 

For now, we will continue to struggle, adhering to our existing protocols until we can figure out the real reason(s) VTE happens, the best ways to prevent, and the best methods to treat.

Related posts:

Reference: Relation of Antifactor-Xa peak levels and venous thromboembolism after trauma. J Trauma accepted for publication Aug 2, 2017.