Tag Archives: IVC

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 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.

The Flat Vena Cava Sign? Published and Revisited

I’ve previously blogged about the flat vena cava sign as an indicator of low volume status in trauma patients. And I commented on this paper when it was presented at EAST, which had a surprisingly negative result. It’s now been vetted by peer reviewers and published, and I’ve had the opportunity to read through the entire manuscript (always important). So let’s take a second look now.

A retrospective study at George Washington University was carried out over a one year period. They looked at all of their highest level trauma activation patients who also underwent CT scan of the abdomen. Images were read by three radiologists and inter-rater reliability was reviewed. The transverse to anteroposterior diameter ratios were calculated to determine flatness.

Here are the factoids:

  • 276 patients met enrollment criteria, and were mostly male and blunt trauma
  • The IVC was nearly round in 21% of patients and collapsed in 26%
  • There was no association between IVC shape and shock index, blood pressure, Hbg, lactate, urgent operation, angiography or length of stay
  • There was also no association between IVC shape and blood transfusion or death
  • Correlation of the reads between radiologists was good

So what gives? A paper I reviewed three years ago in the Journal of Trauma came to a different conclusion. They found that a flat IVC on CT scan (defined as a transverse to AP ratio of 4:1 or greater) was associated with a significantly higher chance of receiving more crystalloid or blood, as well as requiring an operation within 24 hours. 

This newer paper was able to look at a larger group of patients, and they were able to tease out why it initially looked like the flat cava looked like a good predictor for bad things to come. The problem was statistical skewing from a few extreme outliers. When properly corrected, it completely changed things. And looking at the older study, it appears that outliers may have also been the reason for the positive result. This is why I encourage everyone to always read the entire paper! The older paper involved a smaller series (114 patients), but it was prospective and seemed to have reasonable statistical analyses.

image

Bottom line: It looks like the flat vena cava sign, as measured by a static CT, should be discarded as an indicator of impending shock. Whether or not a more dynamic look (using ultrasound) is valuable remains to be determined.

Related post:

Reference: Inferior vena cava size is not associated with shock following injury. J Trauma 77(1):34-39, 2014.