Monthly Archives: April 2011

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Using CT To Diagnose Extremity Vascular Injury

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The traditional gold standard for diagnosis of vascular injury to the extremities has been a good physical exam plus conventional catheter angiography. However, using angiography always adds a layer of complexity and risk to patient care. The interventional team may not be immediately available after hours, there is typically a road trip within the hospital to deliver the patient for the study, and overall it is quite expensive.

With the advancements we have seen in CT angio techniques and scanner technology, some centers have been using computed tomography to evaluate for vascular injury. A few small retrospective studies have been done, but this month a larger prospective study was published.

Over a 20 month period, 635 patients with extremity trauma and a suspicion for vascular injury were entered into the study. A structured physical exam was performed, and any patient with “hard signs” of vascular injury were taken to the OR. 527 patients had no signs of vascular injury and were observed and released. The remaining 73 (most had soft signs of vascular injury) underwent CT angiography of the extremity.

The sensitivity and specificity of this test were 82% and 92%, respectively. Positive and negative results were nearly perfectly predictive. However, approximately 10% were inconclusive, usually due to bullet artifact or reformatting errors. These patients either underwent confirmatory conventional angiography or operation.

Bottom line: Angiography using multi-detector CT scanners is an excellent tool for evaluating potential extremity vascular trauma from penetrating trauma. The technology is available around the clock without a wait, and usually does not involve lengthy trips through the hospital. A good physical exam is imperative so patients with hard signs of injury can go straight to the OR. Equivocal studies must be evaluated further by conventional angio or an operation.

Reference: Prospective multidetector computed tomography for extremity vascular trauma. J Trauma 70:808-815, 2011.

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A New Method For Killing Antibiotic Resistant Bacteria

IBM and the Institute for Bioengineering and Nanotechnology have developed a novel way of wiping out antibiotic resistant bacteria like MRSA. They created a type of nanoparticle that is activated by contact with water. When this occurs, it self-assembles into a new polymer structure that is attracted to infected cells and bacteria, but not healthy cells.

Changes in electrostatic charge on the cell surface attracts the nanoparticles, which then physically break through the cell walls and membranes of bacteria. The nanoparticles then degrade and are excreted.

Bottom line: This is a very exciting line of research. Bacteria multiply and evolve rapidly, sharing genetic information that allows them to change their biochemistry and become resistant to our usual antibiotics. Since the destructive process used by these nanoparticles is purely physical and not biochemical, it will be extremely difficult for any type of resistance to develop. This is an important advance in our efforts to control pathogens.

Reference: Biodegradable nanostructures with selective lysis of microbial membranes. Nature Chemistry, April 3, 2011 (online).

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Evolution of Use of Recombinant Factor VIIa

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Recombinant Factor VIIa was initially approved for bleeding in hemophiliac patients back in 1999. Over the years, there has been a big move toward off-label use. There appeared to be obvious utility in using it as an emergency hemostatic agent in trauma patients. But as with many new drugs and devices, early enthusiasm slowly gave way to more balanced judgment. Reviews during the past few years are less glowing than they were early on. So what’s really been happening over the past decade?

Researchers at Stanford tapped into a large database of patient level records from 600 hospitals around the US. They identified over 18,000 uses of Factor VIIa during a 9 year time period. By the end of the study period (2008), 97% of use was off-label! Approved use (hemophilia) increased 4-fold, while off-label use increased by 140-fold. Cardiovascular surgery and trauma tied in their amount of off-label use (both about 29% of the sample).

Does it do any good? This paper can’t directly address that question, since it does not have a good comparison group. However, looking at in-hospital mortality is revealing. Use for hemophilia (FDA approved) results in a 4% mortality rate. For trauma, the in-house mortality is 33%. The worst outcomes were with patients with an aortic aneurysm (55% mortality). 

Bottom line: This review details the administration of about $175 million worth of recombinant Factor VIIa over 9 years. Off-label use has skyrocketed despite a dearth of good reports that it actually saves lives. The Number Needed to Treat to prevent one additional bad outcome keeps getting larger with every study published. With a price tag of nearly $10,000 per dose, it’s getting harder to justify using it. I think we are seeing the beginning of the end (at least in trauma) for this powerful drug.

Reference: Off-label use of recombinant Factor VIIa in US hospitals: analysis of hospital records. Annals of Int Med 154(8):516-522, 2011.

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Comparison of Cervical Spine Stabilization

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Eight months ago I blogged about inline stabilization vs inline traction of the cervical spine. Click here to read the post. A reader recently asked what the optimal method for inline stabilization is.

We’ve been pondering this question for nearly 30 years. In 1983, trauma surgeons at UCLA looked at a number of devices available at that time and tested them on normal volunteers. They measured neck motion to see which was “best." 

Here’s what they found:

  • Soft collar – In general, this decreased rotation by 8 degrees but insignificantly protected against flexion and extension. Basically, this keeps your neck warm and little else.
  • Hard collars – A variety of collars available in that era were tested. They all allowed about 8% flexion, 18% lateral movement, and 2% rotation. The Philadelphia collar allowed the least extension.
  • Sandbags and tape – Surprisingly, this was the best. It allowed no flexion and only a few percent movement in any other direction.

The Mayo clinic compared four specific hard collars in 2007 (Miami J, Miami J with Occian back, Aspen, Philadelphia). They found that the Miami J and Philadelphia collars reduced neck movement the best. The Miami J with or without the Occian back provided the best relief from pressure. The Aspen allowed more movement in all axes.

And finally, the halo vest is the gold standard. These tend to be used rarely and in very special circumstances.

Bottom line: 

  • For EMS: Rigid collar per your protocol is the standard. In a pinch you can use good old tape and sandbags with excellent results.
  • For physicians: The Miami J provides the most limitation of movement. If the collar will be needed for more than a short time, consider the well-padded Occian back Miami J (see below).

Miami J with Occian back

References:

  • Efficacy of cervical spine immobilization methods. J Trauma 23(6):461-465, 1983.
  • Range-of-motion restriction and craniofacial tissue-interface pressure from four cervical collars. J Trauma 63(5):1120, 1126, 2007.