All posts by TheTraumaPro

EAST 2016: Brain Hypoxia In TBI With Aeromedical Evacuation

I’m sure that most of you have noticed that I very rarely write about animal studies. The problem I have is that the effects generally found are not dramatic, and results seldom carry over to humans the way we think they should. 

But for this paper, I’ve made an exception. It uses a swine model to study the effect of air transport at altitude on TBI. As you may know, most aeromedical transport in the US is via helicopter. 

However, some patients in more rural areas must travel longer distances to get high level trauma care, and may need to fly in fixed wing aircraft. U.S. military transports overseas use fixed wing almost exclusively. 

Medical helicopters typically fly at only 1000-3000 feet above the ground, and the change in air pressure (and hence PaO2) is small. However, fixed wing aircraft fly at much higher altitudes, and the effective cabin altitude may rise to about 8000 feet. This is why your ears “pop” so many times as you ascend. You’ve essentially just climbed Mt. St. Helens in Washington state. The amount of oxygen in cabin air also decreases with altitude.

So what happens to a patient with severe TBI when exposed to these fluctuations in pressure and oxygen levels? A group at the Naval Research Center looked at this issue in anesthetized swine that received a TBI from a percussion device. They received standard TBI and injury-specific care (for pigs?) for two hours, then underwent flight simulation using a hypobaric chamber set to a cabin altitude of 8000 feet for four hours. 

Here are the factoids:

  • Six study pigs underwent the 2 hours at sea level followed by 4 hours at altitude. Six control pigs stayed at sea level after their injury.
  • Mean arterial pressure in the pigs at altitude decreased somewhat, but not significantly.
  • Intracranial pressure (ICP) increased significantly in the TBI group(!)
  • As a result, cerebral perfusion pressure (CPP) dropped in the study group (highly significant result).

Bottom line: Aeromedical transport at typical cabin altitudes significantly increases ICP and decreases CPP in an injured pig model. Although the groups are small, this information is startling and deserves rapid confirmation. This information may have a significant impact on the way we fly patients with head injuries. In particular, this is important for military aeromedical evacuation.

Reference: Brain hypoxia is exacerbated in hypobaria during aeromedical evacuation in swine with TBI. EAST 2016 Oral abstract #2, resident research competition.

EAST 2016 Is Coming!

The Eastern Associate for the Surgery of Trauma (EAST) holds its annual scientific assembly every year in January, typically in a nice, warm location. This year is no exception, as it will be taking place in the JW Marriott in San Antonio. 

The program is usually quite varied, and there are always two special sessions that are devoted to prevention and presentations from young researchers. This organization caters to young trauma professionals, and strives to get them involved in its various committees early in their careers. And it provides invaluable networking opportunities in a very informal setting. 

In recent years, the scientific program has been a bit ho-hum. However, I’ve been reviewing this year’s abstract selection and have found quite a few exciting papers. I’m going to share my comments on one interesting abstract a day for the next 2 weeks.

But remember, these analyses are based on reading the abstracts alone. Sometimes the actual work presented varies substantially so I urge you to attend and listen to the talks yourself.

And just for giggles, I’ve included one example on how not to write your abstract. I’ll publish that one next Monday.

Enjoy!

What’s The Best Pelvic Binder? Part 2

Yesterday, I detailed some pelvic binders commonly available
in the US.
Today, I’ll go through the (little) science there is regarding which are better
than others.

There are a number of factors to consider when choosing one
of these products.
They are:

  • Does it work?
  • Does it hurt or cause skin damage?
  • Is it easy to use?
  • How much does it cost?

It’s difficult to determine how well binders work in the live,
clinical setting. But biomechanical studies can serve as a surrogate to try to answer
this question. One such cadaver study was carried out in the Netherlands a
few years ago. They created one of three different fracture types in pelvis
specimens. Special locator wires were placed initially so they could measure bone movement
before and after binder placement. All three of the previously discussed
commercial binders were used.

Here are the factoids:

  • In fracture patterns that were partially stable or unstable,
    all binders successfully closed the pelvic ring.
  • None of the binders caused adverse displacements of fracture
    fragments.
  • Pulling force to achieve complete reduction was lowest with
    the T-POD (40 Newtons) and highest with the SAM
    pelvic sling (120 Newtons).
    The SAM sling limits compression to 150 Newtons,
    which was more than adequate to close the pelvis.

So what about harm? A healthy volunteer study was used to
test each binder for tissue pressure levels. The 80 volunteers were outfitted
with a pressure sensing mat around their pelvis, and readings were taken with
each binder in place.

Here are the additional factoids:

  • The tissue damage threshold was assumed to be 9.3 kPa
    sustained for more than 2-3 hours based on the 1994 paper cited below.
  • All binders exceeded the tissue damage threshold at the
    greater trochanters and sacrum while lying on a backboard. It was highest with
    the Pelvic Binder and lowest with the SAM sling.
  • Pressures over the trochanters decreased significantly after
    transfer to a hospital bed, but the Pelvic Binder pressures remained at the
    tissue damage level.
  • Pressures over the sacrum far exceeded the tissue damage pressure
    with all binders on a backboard and it remained at or above this level even
    after transfer to a bed. Once again, the Pelvic Binder pressures were higher. The
    other splints had similar pressures.

And finally, the price! Although your results may vary due to
your buying power, the SAM sling is about $50-$70, the Pelvic Binder $140, and
the T-POD $125.

Bottom line: The binder that performed the best (equivalent
biomechanical testing, better tissue pressure profile) was the SAM sling. It also happens to be the least expensive, although it takes a little more elbow grease to apply. In my mind, that’s a winning combo.
Plus, it’s narrow, which allows easy access to the abdomen and groins for
procedures. But remember, whichever one you choose, get them off as soon as
possible to avoid skin complications.

What’s the best pelvic binder? Part 1

References:

  • Comparison of three different pelvic circumferential
    compression devices: a biomechanical cadaver study. JBJS 93:230-240, 2011.
  • Randomised clinical trial comparing pressure characteristics
    of pelvic circumferential compression devices in healthy volunteers. Injury 42:1020-1026,
    2011.
  • Pressure sores. BMJ 309(6959):853-857, 1994.

What’s The Best Pelvic Binder? Part 1

Several products for compressing the fractured pelvis are available. They range from free and simple (a sheet), to a bit more complicated and expensive. How to decide which product to use? Today, I’ll discuss the four commonly used products. Tomorrow, I’ll look at the science.

First, let’s dispense with the sheet. Yes, it’s very cheap. But it’s not easy to use correctly, and more difficult to secure. Click here to see my post on its use.

There are three commercial products that are commonly used. First is the Pelvic Binder from the company of the same name (www.pelvicbinder.com). It consists of a relatively wide belt with a tensioning mechanism that attaches to the belt using velcro. One size fits all, so you may have to cut down the belt for smaller patients. Proper tension is gauged by being able to insert two fingers under the binder.

Next is the SAM Pelvic Sling from SAM Medical Products (http://www.sammedical.com). This device is a bit fancier, is slimmer, and the inside is more padded. It uses a belt mechanism to tighten and secure the sling. This mechanism automatically limits the amount of force applied to avoid problems with excessive compression. It comes in three sizes, and the standard size fits 98% of the population, they say.

Finally, there is the T-POD from Pyng Medical (http://www.pyng.com/products/t-podresponder). This one looks similar to the Pelvic Binder in terms of width and tensioning. It is also a cut to fit, one size fits all device. It has a pull tab that uses a pulley system to apply tension. Again, two fingers must be inserted to gauge proper tension. 

So those are the choices. Tomorrow, I’ll go over some of the data and pricing so you can make intelligent choices about selecting the right device for you.

Related posts:

Trauma MedEd Newsletter: The Best Of EAST Part 2!

I’m still not done reviewing abstracts from next month’s annual meeting of the Eastern Association for the Surgery of Trauma (EAST). There are yet more oral and poster abstracts that I want to pick apart. Here are some that are coming in the January issue:

  • How long is DVT a potential risk in TBI?
  • Measuring volume status using jugular ultrasound
  • Pain as a predictor of tourniquet efficiency p23
  • Nursing interruptions in the SICU p18
  • And more…!

Anyone on the subscriber list when the ball drops on New Year’s Eve (CST) will receive it later that day. Everybody else will have to wait for me to release it here on the blog late next week. So sign up for early delivery now by clicking here!

Pick up back issues here!