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. (!!)
  • 30% 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.

Source: The Trauma Professionals’s Blog

The Lowly Blood Pressure Cuff: Is It Accurate?

Yesterday, I described how the typical automated oscillometric blood pressure cuff works. We rely on this workhorse piece of equipment for nearly all pressure determinations outside of the intensive care unit. So the obvious question is, “is it accurate?”

Interestingly, there are not very many good papers that have ever looked at this! However, this simple question was addressed by a group at Harvard back in 2013. This study utilized an extensive ICU database from 7 ICUs at the Beth Israel Deaconess Medical Center. Seven years of data were analyzed, including minute by minute blood pressure readings in patients with both automated cuffs and indwelling arterial lines. Arterial line pressures were considered to be the “gold standard.”

Here are the factoids:

  • Over 27,000 pairs of simultaneously recorded cuff and arterial line measurements from 852 patients were analyzed
  • The cuff underestimated art line SBP for pressures at or above 95 torr
  • The cuff overestimated SBO for pressures below 95 torr (!)
  • Patients in profound shock (SBP < 60) had a cuff reading 10 torr higher
  • Mean arterial pressure was reasonably accurate in hypotensive patients

sbp-cuff-v-aline

Bottom line: The good, old-fashioned automated blood pressure cuff is fine for patients with normal pressures or better. In fact, it tends to understimate the SBP the higher it is, which is fine. However, it overestimates the SBP in hypotensive patients. This can be dangerous! 

You may look at that SBP of 90 and say to yourself, “that’s not too bad.” But really it might be 80. Would that change your mind? Don’t get suckered into thinking that this mainstay of medical care is perfect! And consider peeking at the mean arterial pressure from time to time. That may give you a more accurate picture of where the patient really is from a pressure standpoint.

Related posts:

Reference: Methods of blood pressure measurement in the ICU. Crit Care Med Journal, 41(1): 34-40, 2013.

 

Source: The Trauma Professionals’s Blog

How Does It Work? The Lowly Blood Pressure Cuff

The blood pressure cuff is one of those devices trauma professionals don’t give a second thought to. Old timers like me remember using the cuff with a sphygmomanometer and stethoscope to get manual blood pressures. I’ve had to do this twice in recent months on airplanes, and I had forgotten how much work this is.

But technology makes things easier for us. Now you just slap a cuff on the arm (or wrist), push a button, and voila! You’ve got the pressure.

But have you stopped to think about how this actually works? Why don’t we need the stethoscope any more? Here’s the scoop:

When you take a manual blood pressure, the cuff is inflated until a pulse can no longer be auscultated with the stethoscope. The pressure is slowly released using a little thumb wheel while listening for the pulse again. The pressure at which it is first audible is the systolic, and the pressure at which it softens and fades away is the diastolic.

The automatic blood pressure device consists of a cuff, tubing that connects it to the monitor, a pressure transducer in line with the tubing, a mini air pump, and a small computer. The transducer replaces the analog pressure gauge, and the pump and computer replace the human.

The transducer can “see” through the tubing and into the cuff. It is very sensitive to pressure and pressure changes. The computer directs the pump to inflate to about 20 torr above the point where pulsations in the air column cease. It then releases the pressure at about 4 torr per second, “feeling” for air column vibrations to start. When this occurs, the systolic pressure is recorded. Deflation continues until the vibrations stop, representing the diastolic pressure.

bpcuff

Piece of cake! But here’s the question: is it accurate? Tomorrow, I’ll write about how the automated cuff compares to an indwelling arterial line.

Related post:

Source: The Trauma Professionals’s Blog

How Many Salt Tabs In A Liter Of Saline?

Seems like a simple, silly question, right? I dare you to figure it out without reading this post!

horse-salt-block-lick2

On occasion, our brain injured trauma patients have sodium issues. You know, cerebral salt wasting. Trying to maintain or regain the normal range, without making any sudden moves can be challenging. There are a lot of tools available to the trauma professional, including:

  • Saline
  • Hypertonic saline
  • Salt tablets
  • Fluid restriction
  • Some combination thereof

Fun times are had trying to figure out how much extra sodium we are giving with any of the first three items. This is important as you begin to transition from the big guns (hypertonic), to regular saline, and then to oral salt tabs.

Below is a quick and dirty conversion list. I won’t make your heads explode by trying to explain the math involved changing between meq, mg, moles, sodium and sodium chloride.

  • The “normal saline” bags we use are actually 0.9% saline (9 gm NaCl per liter)
  • Hypertonic saline can be 3% or 5% (30 gm or 50 gm per liter)
  • Salt tabs are usually 1 gm each (and oh so yummy)

Therefore, a liter of 0.9% normal saline is the same as 9 salt tabs.

A liter of 3% hypertonic saline is the same as 30 salt tabs. The usual 500cc bag contains 15.

A liter of  5% hypertonic saline is the same as 50 salt tabs. The usual 500cc bag contains 30.

To figure out how many tablets you need to give to match their IV input, calculate the number of liters infused, then do the math! And have fun!

Source: The Trauma Professionals’s Blog

Next Trauma MedEd Newsletter Is Coming Next Week!

As promised, the next Trauma MedEd newsletter will be released next week. Just in time for some light Christmas reading!

The topic is “Prevention.” Here are the areas I’ll be covering:

  • The American College of Surgeons requires all US trauma centers to engage in prevention activities. Unfortunately, there is frequently confusion about the role of the injury prevention coordinator, what kinds of programs are acceptable, and how local data needs to be included in prevention planning. I will cover all of this, and more, in the first part of the newsletter.
  • Curious about what others are doing out there? I’ll give you an idea of the most common prevention programs, and whether they are national programs or home grown.
  • I’ll review a few papers on the efficacy of trauma prevention programs.
  • Finally, I’ll give some tips on how to optimize the performance of your injury prevention coordinator and design effective programs.

As always, this issue will go to all of my subscribers first. If you are not yet one of them, click this link to sign up and/or download back issues.

Unfortunately, non-subscribers will have to wait until I release the issue on this blog, sometime during the week after Christmas. So sign up now!

Source: The Trauma Professionals’s Blog

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.

Source: The Trauma Professionals’s Blog

(Mis)Use of Helicopter Transport For Pediatric Trauma

Helicopter transport is an integral and important part of modern day trauma care. Since the inception helicopter emergency medical services (HEMS) for civilian use in the 1970’s, its use has been steadily increasing. And it’s expensive, at least five times more costly than ground transport. Plus, there are risks to both crew and patient, in that there have been 200 deaths of both patients and flight crews. Indeed, flight crews have one of the riskiest jobs, with 5 times more on-the-job deaths than police officers.

So it becomes very important to make sure that this mode of transport is justified. As I wrote previously, the adult HEMS literature is extensive, but not terribly convincing. There is far less data available regarding pediatric patients. And the data that does exist suggests that there may be significant overtriage and overuse.

A study using the National Trauma Data Bank (NTDB) was performed by researchers at Duke University. They reviewed the data for a 5 year period (2007-2011), which is fairly old in my opinion. And they included “children” up through age 18, which are also a bit old, in my opinion. Since there are no real quantitative criteria for overtriage in place, the authors picked three: low injury severity (ISS<10), normal physiology (RTS=12), and low predicted mortality using TRISS (<5%). A total of 127,489 patient records were analyzed.

Here are the factoids:

  • 14% arrived via helicopter EMS,  56% by ground EMS, and 29% by private vehicle or walk-in
  • HEMS patients were more likely to have head, thoracic, or abdominal injuries, and overall severe injuries (good!)
  • Adjusted mortality for patients transported by air was significantly less than for ground (really good)
  • 38% of HEMS patients had ISS < 9, and 66% had completely normal physiology (bad)
  • Overall, 32% to 82% of children did not meet criteria for appropriate transport

Bottom line: There are a number of flaws in this study that could be improved upon. However, it does provide some interesting data. Helicopter transport does save lives in the younger population, and was estimated at 2 per 100 flights. This is very promising. However, offsetting this was the fact that nearly half of transports failed one or more arbitrary appropriateness criteria. The recommendations I published yesterday need to be adopted, and both state trauma systems and local EMS agencies need to develop and enforce guidelines to optimally use this valuable and expensive resource.

Reference: Current use and outcomes of helicopter transport in pediatric trauma: a review of 18,291 transports. J Ped Surg in press 27 Oct 2016.

Source: The Trauma Professionals’s Blog

Helicopter EMS: The Recommendations

So after two days of pros and cons about helicopter EMS (HEMS), we lead up to this. The American College of Surgeons Committee on Trauma, Emergency Medical System subcommittee, has released a set of guidelines on appropriate use of HEMS. It’s been endorsed by the National Association of EMS Physicians and looks like a lot of thought has gone into it.

Here are the factoids about the HEMS guidelines:

  • Must be integrated with your trauma system
  • Must utilize standardized field triage guidelines that should be applied consistently throughout your trauma system
  • Is blind to the insurance status of the patient
  • Uses a regional dispatch system. Self-launch should never happen.
  • Referring physician to receiving physician conversations must occur when considering transportation mode (air vs ground) for interfacility transfers
  • There must be good online medical direction from a physician
  • Offline medical direction must be based on protocols and policies developed by the trauma system
  • There must be regular PI review of all HEMS transports to ensure compliance
  • HEMS crews must have regular training opportunities
  • A culture of safety must be maintained

Bottom line: We absolutely must take a critical look at our patient transport practices and procedures. To ensure even-handed application of best practices, our state trauma systems are going to have to step up and address this issue so the right patient will get to the right hospital at the right time, safely and cost effectively.

Reference: Appropriate use of Helicopter Emergency Medical Services for transport of trauma patients: Guidelines from the Emergency Medical System Subcommittee, Committee on Trauma, American College of Surgeons. J Trauma 75(4):734-741, 2013.

Source: The Trauma Professionals’s Blog

Helicopter EMS: The Risks

Yesterday, I wrote about the (unclear) benefits of helicopter EMS transports. Today, I’ll cover the risks. The number of medical helicopters in the US has grown dramatically since 2002.

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As can be expected, the number of mishaps should go up as well.

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Although it looks like the fatal and injury accidents peaked and then declined, it does not look as good when compared to the rest of the aviation industry. Consequently, being on a helicopter EMS (HEMS) crew has become one of the more dangerous professions.

image

And unfortunately, the numbers have not improved much during the past five years. So what to do? Make it a big PI project. Approach it systematically, analyze the issues, and create some guidelines and protocols for all to follow.

Tomorrow, I’ll review  guidelines for HEMS released by the American College of Surgeons Committee on Trauma.

Reference: Medical helicopter accidents in the United States: a 10 year review. J Trauma 56:1325-1329, 2004.

Source: The Trauma Professionals’s Blog

Helicopter EMS (HEMS): The Benefits?

I’m going to kick off 4 days of information on helicopter emergency medical services (HEMS).

The use of medical helicopters has grown at an astonishing rate in the 10+ years since Medicare got involved with payment for this service. All high level trauma centers have helicopter landing facilities, and many either own or are a part owner in at least one helicopter EMS service (HEMS).

Here’s a state by state breakdown of the number of medical helicopters:

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It’s gotten to the point where the indication for summoning a HEMS service seems to be the presence of a patient to ride on it! 

A lot of papers have been published in the past 20 years trying to justify the benefits of using these services. As is the usually case when a lot of papers are published on one subject, most of them are not very good. Many studies have been performed to try to justify their use, and most were not successful. The following items have been scrutinized:

  • Interfacility transfers
  • Trauma
  • Pediatric transfers
  • Pediatric trauma
  • Burns
  • OB
  • Neonatal
  • Rural trauma

Most of these papers found little, if any, benefit. The ones that did tended to be published by institutions that owned these services, raising the significant question of bias. The one thing that was always significantly different was the cost. HEMS costs at least 5-10 times more than ground EMS transport.

So the benefits are not very clear. What about the risks? I’ll talk about those in my next post.

Click here to view the interactive state map of medical helicopters. See where your state is with respect to number of ships and services, and how busy they are.

Source: The Trauma Professionals’s Blog

The Regions Trauma Website