Category Archives: Complications

EAST 2017 #3: My Neck Is Broken And It Doesn’t Hurt?

Clinical clearance of the cervical spine is a standard of care. It is usually the first method to determine if there might be an injury in patients who are awake, cooperative, and don’t have other painful distracting injuries. But appreciation of pain may be different in elderly patients, and they will frequently not notice pain from some injuries. Could this possibly impact clearance of the cervical spine?

A group at Iowa Methodist performed a retrospective review of patients > 55 with diagnosed cervical spine fractures over a four year period. They were considered to have an asymptomatic injury if they did not complain of pain, or of tenderness to palpation.

Here are the factoids:

  • A total of 173 elderly patients presented with a cervical spine injury during the study period
  • 38 of them (22%) were asymptomatic
  • The asymptomatic patients tended to have higher injury severity (ISS 15 vs 10), have a significant injury in another body region (71% vs 47%), and stayed in the hospital longer (7 days vs 5)
  • A third of patients had multiple cervical fractures (symptomatic or asymptomatic?)
  • C2 was the most common fracture level

Bottom line: I have witnessed this phenomenon myself. Not all of our elders perceive pain the same way younger patients do. This study shows that it is a very significant problem. Most of the previous papers and the only review I could find do not separate out the elderly when making cervical clearance recommendations. We will probably have to develop some specific criteria to determine when a CT scan is necessary in the asymptomatic elderly patient. In the algorithm used at my hospital, age > 65 is already used to bypass clinical clearance. Looks like I’ll have to drop that to 55!

Questions and comments for the authors/presenters:

  • Since they were asymptomatic, how do you know that you didn’t miss any patients?
  • Do you have a practice guideline for cervical spine evaluation? Has it changed based on your study?
  • Be sure to break your data down by mechanism of injury for the presentation. Were there more asymptomatic patients from falls rather than car crashes? Associated fracture patterns for each mechanism?
  • What do you now recommend for clearance?
  • Suggestion: change your title to “cervical spine fractures”, not “neck fracture”.

Click here to go the the EAST 2017 page to see comments on other abstracts.

Related posts:

Reference:   Asymptomatic neck fractures: current guidelines can fail older patients. Paper #8, EAST 2017.

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Enoxaparin And anti-Xa Levels: Who Cares? Part 3

Today is the final installment in a series about the use of anti-Factor Xa levels to titrate enoxaparin dosing to prevent venous thromboembolism (VTE). This is another study that tries to show that “hitting the number” actually makes a difference in patient care. You decide.

This study identified a subset of patients at high-risk for VTE based on a commonly used and very good risk screening tool, the Risk Assessment Profile (RAP). It takes some 17 factors into account to arrive at a numerical score. In this paper, the authors chose a score of 10 or greater to denote high risk. The patients were all seriously injured, and were in the trauma ICU of this established Level I trauma center.

This retrospective study excluded non-ICU patients, ones who did not receive enoxaparin or anti-Xa levels, and two patients with DVT on admission. This brought the number of eligible patients from 621 to 127 (the treatment group). They then narrowed the field down to the high-risk treatment group by excluding patients with a RAP score < 10. Now we are down to 86. But then 30 more (35%) were excluded because they did not undergo duplex ultrasound screening, leaving only 56 to study (!).

The control group was a “similar” historical cohort from a two year period from 2009 to 2012. You can tell that this group is getting a little stale, because the only patients included were those who received unfractionated heparin for prophylaxis (remember those days?). Of the 106 patients in the control group, 20 (28%) were reported as have VTE. However, it included 6 patients with DVT on admission, which were excluded in the study group. This makes the DVT rate look higher in the control group. It also included 2 upper extremity DVT and 1 septic pelvic venous thrombosis. Excluding all of these brings the historical VTE rate down to only 10%. Remember this.

So let’s get on to the factoids:

  • Only 35% of the 127 patient treatment group “hit the number” for anti-Xa (0.2-0.4 IU/ml) after three 30mg doses of enoxaparin
  • An additional 25% managed to achieve the desired anti-Xa level after dose adjustment, but 51 patients (40%) never did get there
  • There were 10 VTE events in the 127 treatment group patients, 9 of whom had high RAP scores, giving them a 7.8% rate of VTE
  • Nine of the 10 VTE patients occurred in patients with low anti-Xa levels
  • The authors compared their 7.1% DVT rate with the 21% in their historical controls, concluding that titrating anti-Xa levels reduced this rate. They did not include PE for some reason, and do not claim a statistical difference. They admit that the study was underpowered to detect differences in VTE. There is no significant difference in VTE rates in the study or control groups.

Bottom line: This is the last paper on the topic. I promise. At least for a while. Here’s what we know:

  • VTE is a problem in trauma patients, particularly seriously injured ones
  • We are not very good at sticking to a prophylaxis or screening regimen (note how many patients are excluded in all of these studies)
  • We can’t seem to generate the numbers to conduct a good study that can detect differences in what we do
  • It’s difficult to “hit the number” for anti-Xa using standard enoxaparin dosing
  • We don’t even know if it makes a difference if we do “hit the number”. VTE rates seem to be the same regardless.

So we are struggling to make a lab test look right to adjust enoxaparin dosing, and we don’t even know if it makes a difference. Will somebody put a good, multi-center study together and help us to figure all of this out?

Related posts:

Reference: Anti-Xa-guided enoxaparin thromboprophylaxis reduces rate of deep venous thromboembolism in high-risk trauma patients. J Trauma 81(6):1101-1108, 2016.

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Enoxaparin And anti-Xa Levels: Who Cares? Part 1.5

Oops, I’ve got to backtrack a little. I just ran across a newly published study from the authors mentioned in Part 1 of this series a few days back. I pointed out some of the issues that surfaced as they tried to “hit the numbers” for factor anti-Xa levels in patients from their hospital. Here’s a breakdown of the new study.

First, I love the beginning of the title:

“If some is good, more is better”

Really?

Recognizing that 30% of patients had low anti-Xa trough levels when given the standard 30mg bid dosing regimen for enoxaparin, the authors engaged in some fancy predictive and statistical models to come up with a new one. A good portion of the methods section of the paper is devoted to explaining the machinations of exactly how they did this.

They used a patient dataset that was a little fresher than from Part 1. Three years of data from 2011 to 2014 were reviewed, and 275 patients were used to generate the new models. They selected one of seven candidates, based on a combination of simplicity and fewer supranormal levels of anti-Xa. They used this model to guide dosing to the next 145 patients. Here is the new regimen:

Weight Dose (q 12 hrs)
50-60 kg 30 mg
61-99 kg 40 mg
> 100 kg 50 mg

And here are the factoids:

  • Of the 275 patients used to create the model, 70% were subtherapeutic. (This is exactly the same number as in the first paper, but a different number of patients. Hmm.)
  • With the new dosing regimen in place, only 21% were subtherapeutic
  • Patients with supratherapeutic anti-Xa levels increased from 2 to 5% using the new routine
  • VTE was the same, at about 3-4%
  • Four patients developed VTE on the new regimen, and 3 of them had therapeutic anti-Xa levels (!)

Bottom line: A lot of modeling and statistical work went into the production of this paper. I still wonder why the number of patients included over 3 years is so low for such a busy center. But the authors certainly showed that they could improve the rate at which they “hit the number.” But how important is this, really?

The concluding sentence of the abstract reads, “further studies are needed to determine whether such dosing decreases venous thromboembolism rates.” Perhaps we should figure that out before continuing to spend lots of time playing with dosing changes and blood tests.

Reference: If some is good, more is better: an enoxaparin dosing strategy to improve pharmacologic venous thromboembolism prophylaxis. J Trauma 81(6):1095-1100, 2016.

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Enoxaparin And anti-Xa Levels: Who Cares? Part 2

In my last post, I reviewed a study that looked at monitoring factor anti-Xa for the purpose of just “hitting the number.” Not very convincing. Today, I’ll review one that studied a reasonable outcome, the actual occurrence of VTE in patients.

This was another small, prospective study at a busy Level I trauma center. The outcomes that were analyzed included LOS, transfusion requirement, hematocrit on discharge, and diagnosis of deep venous thrombosis (DVT) or pulmonary embolism (PE). Only the last two of these make sense, especially for this small study. (205 patients in two 10 month periods).

At this center, all trauma patients are started on enoxaparin, regardless of injury severity. And all patients have sequential compression devices applied unless contraindicated by their injuries. Patients were included if the were administered 3 consecutive enoxaparin doses and had a trough anti-Xa level measured an hour before the fourth dose. If the trough was less than 0.1 IU/ml, dosing was adjusted until it rose to > 0.2 IU/ml. Outcomes were compared to historical controls from the prior year.

Here are the factoids:

  • A total of 87 study patients were enrolled in 10 months.  However, this represents only about 15% of trauma admissions to the center. Why were so few eligible for inclusion?
  • 84% of study patients did not “hit the number” with 30mg bid dosing (again!)
  • They were compared to 118 control patients who received enoxaparin during the same 10 month period, a year earlier
  • Screening by duplex ultrasound was only done for “clinical suspicion” of DVT or PE. No routine screening. And we know how reliable clinical suspicion can be.
  • 84% of patients were not at their anti-Xa goal when the first trough was done. Most of these patients needed 40mg bid to “hit the number.”
  • DVT and PE occurrences were “significantly lower” in the dose adjusted group compared to historical controls (1.1% vs 7.6%). Now this is a difference between only 1 adjusted patient and 9 controls, and the p value barely made it at 0.046.
  • Proximal DVT occurred  in no adjusted patients vs 2 controls (not significant)
  • PE occurred in no adjusted patients and 1 control (not significant)
  • Distal DVT occurred in 1 adjusted patient and 6 controls (not significant

Bottom line: This is yet another (very) small study. It also demonstrates why you must read the study, not just the abstract! The study group was a fraction of all of the patient admitted, even though all patients supposedly received prophylaxis. The attending physicians decided when to start dosing, and this varied from 0 to 4 days. Screening was ordered only if there was some kind of clinical suspicion for DVT or PE, and the details were not spelled out. 

For all these reasons, there are many, many opportunities for bias. But probably the most important problem is the statistics. I always worry when the p value for a numerical difference barely reaches 0.05, especially when the actual numbers look to be far apart. It is usually an indicator of small study size.

But in this case, the breakdown of VTE location is critical. The sums of the distal, proximal, and pulmonary occurrences show a p value difference just under 0.05. But when you compare study vs control for each, the bulk of the numbers are due to distal DVT.  The literature does not convincingly support prophylaxis for distal DVT, and we do not even treat it at my center. We continue surveillance to make sure it doesn’t creep up into the popliteal arteries.

This is yet another weak study trying to make the case for anti-Xa monitoring that doesn’t pass muster. Again, we see that 30mg bid doesn’t “hit the number” without adjustment. But we also haven’t shown that hitting that magic number of 0.2 IU/ml (peak or trough) by adjusting the dose makes a difference either.

But we continue to try. In my next post, we’ll look at another recently published study on the same topic.

Related posts:

Reference: Association between enoxaparin dosage adjusted by anti-factor Xa trough level and clinically evident venous thromboembolism after trauma. Jama Surg. Published online ahead of print July 6, 2016.

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

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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