Category Archives: Complications

Complications

Enoxaparin And anti-Xa Levels: Who Cares? Part 1

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Several papers have been published in recent years analyzing the process of fine-tuning venous thromboembolism (VTE) prophylaxis with enoxaparin. My own hospital has (or had) a protocol in place to automatically draw anti-Xa levels after the third enoxaparin dose in select patients. What is the science behind this concept? It looks like that’s a popular question these days.

Enoxaparin interacts with antithrombin III, turning off a number of factors further down in the clotting cascade. As part of the process, it inactivates Factor Xa, which is easily measurable by a simple blood test. This is very helpful, since PT and PTT are not affected by enoxaparin.

The paper I will discuss today postulated that many patients are “sub-therapeutic” given the usual dosing regimen of 30mg bid. They primarily focused on “hitting the number”, meaning achieving an anti-Xa level > 0.2 IU/ml.

Patients at a single Level I trauma center were enrolled, receiving standard dose enoxaparin and undergoing duplex screening within 48 hours of admission, and again during the first week in hospital. Anti-Xa levels were drawn four hours after the third dose (peak level) and one hour before the fourth dose (trough level).

Here are the factoids:

  • Of 164 patients enrolled, only 61 patients remained in the study. A total of 103 (63%) were excluded because blood draws or screening studies were not done correctly. (!!)
  • 70% of patients had sub-therapeutic enoxaparin dosing based on anti-Xa peak levels
  • The subtherapeutic patients tended to be males, with “higher body weight.” The reality was that the therapeutic patients weighed 71kg and the non-therapeutic men 88kg. But BMI was only 25 and 29, respectively, and was not significantly different.
  • There were 3 VTEs detected during the study, all receiving the initial 30mg dose of enoxaparin. Two of the three had therapeutic anti-Xa levels.
  • No bleeding complications were observed in patients who had their enoxaparin dose adjusted upward

Bottom line: It’s really hard to take anything away from this study at all! Well, we can certainly see that the research group had a tough time adhering to their own protocol, losing two thirds of their study group. This throws the accuracy of the data on the remaining subjects into doubt given the very low numbers.

It would appear that many patients did not achieve their magic number of 0.2 IU/ml for anti-Xa when receiving the standard enoxaparin dose. So what? VTE occurred essentially equally in both groups, but really can’t be interpreted either due to the low numbers.

So basically, this paper is just telling us how many of their patients don’t hit the magic number. Not if that number has any implications on real outcomes, like DVT, PE, or mortality. But if you only read the title or abstract, you might think so!

Tomorrow, I’ll review a paper on anti-Xa that takes a different approach. Just about as successfully.

Related posts:

Reference: Dose adjusting enoxaparin is necessary to achieve adequate venous thromboembolism prophylaxis in trauma patients. J Trauma 745(1):128-135, 2013.

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Complications

A Sample Final Damage Control X-ray

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Yesterday, I wrote about ways to reduce and hopefully eliminate retained foreign bodies (instruments, sponges) during damage control surgery. Today, I’ll provide a sample x-ray and some tips on how to use this tool most effectively.

Here is an abdominal x-ray obtained just prior to closure of a patient who underwent damage control laparotomy. The OR record and surgeon from the initial operation documented that four sponges had been left in place for hemostasis.

dc-closure

Nothing retained, right?

Wrong! This image is not complete. This patient is larger than the x-ray plate used. The area under the diaphragms, the pelvis, and the entire left side of the peritoneal cavity have not been visualized.

Tips for imaging for damage control closure:

  • Always make sure the patient is on an x-ray OR table. It is so annoying (and potentially a sterility problem) to have to slide the plate under the patient!
  • Help the radiology tech to locate the desired imaging field using folds in the towels covering the body region. For example place the confluence of folds in the center of the towel in the exact place you want the center of the x-ray to be.
  • Remove all radiopaque objects from the x-ray field to reduce confusion when interpreting the image
  • Make sure the entire body cavity has been imaged! This may mean bracketing the area with several shots.
  • Read the image yourself! But if in doubt, or in patients with drains or other odd objects, call the radiologist to help you out.

Related posts:

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Complications

The Final X-Ray In Damage Control Surgery

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Damage control surgery for trauma is over 20 years old, yet we continue to find ways to refine it and make it better. Many lives have been saved over the years, but we’ve also discovered new questions. How soon should the patient go back for definitive closure? What is the optimal closure technique? What if it still won’t close?

One other troublesome issue surfaced as well. We discovered that it is entirely possible to leave things behind. Retained foreign bodies are the bane of any surgeon, and many, many systems are in place to avoid them. However, many of these processes are not possible in emergent trauma surgery. Preop instrument counts cannot be done. Handfuls of uncounted sponges may be packed into the wound.

I was only able to find one paper describing how often things are left behind in damage control surgery (see reference below), and it was uncommon in this single center study (3 cases out of about 2500 patients). However, it can be catastrophic, causing sepsis, physical damage to adjacent organs, and the risk of performing an additional operation in a sick trauma patient.

So what can we do to reduce the risk, hopefully to zero? Here are my  recommendations:

  • For busy centers that do frequent laparotomy or thoracotomy for trauma and have packs open and ready, pre-count all instruments and document it
  • Pre-count a set number of laparotomy pads into the packs
  • Use only items that are radiopaque or have a marker embedded in them. This includes surgical towels, too!
  • Implement a damage control closure x-ray policy. When the patient returns to OR and the surgeons are ready to begin the final closure, obtain an x-ray of the entire area that was operated upon. This must be performed and read before the closure is complete so that any identified retained objects can be removed.

Tomorrow, a sample damage control closure x-ray.

Related post:

Reference: Retained foreign bodies after emergent trauma surgery: incidence after 2526 cavitary explorations. Am Surg 73(10):1031-1034, 2007.

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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.
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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.

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