Tag Archives: imaging

Imaging

Part 1: Metal Splints – Can You X-ray Through Them?

Leave a comment

Splinting is an important part of the trauma resuscitation process. No patient should leave your trauma resuscitation room without splinting of all major fractures. It reduces pain, bleeding, and soft tissue injury, and can keep a closed fracture from becoming an open one.

But what about imaging? Can’t the splint degrade x-rays and hamper interpretation of the fracture images? Especially those pre-formed aluminum ones with the holes in them? It’s metal, after all.

Some of my orthopedic colleagues insist that the splint be removed in the x-ray department before obtaining images. And who ends up doing it? The poor radiographic tech, who has no training in fracture immobilization and can’t provide additional pain control on their own.

But does it really make a difference? Judge for yourself. Here are some knee images with one of these splints on:

Amazingly, this thin aluminum shows up only faintly. There is minimal impact on interpretation of the tibial plateau. And on the lateral view, the splint is well posterior to bones.

On the tib-fib above, the holes are a little distracting on the AP view, but still allow for good images to be obtained.

Bottom line: In general, splints should not be removed during the imaging process for acute trauma. For most fractures, the images obtained are more than adequate to define the injury and formulate a treatment plan. If the fracture pattern is complex, it may be helpful to temporarily remove it, but this should only be done by a physician who can ensure the fracture site is handled properly. In some cases, CT scan may be more helpful and does not require splint removal. And in all cases, the splint should also be replaced immediately at the end of the study.

In my next post, I’ll look at the use of CT scans when this type of splint is in use.

 

Imaging

How Much Radiation Exposure In Imaging Studies?

2 Comments

Everyone knows that CT scans deliver more radiation than conventional x-ray. But how much does each test really deliver? And how significant is that?

Let me try to put it all into perspective. First, how much radiation are we exposed to just living outside the hospital? Background radiation is everywhere. It consists of radioactive gases (argon) in the air we breathe, radiation from the rocks and other things around us, and cosmic rays blasting through us from space.

In the United States, the average background radiation each of us is exposed to is about 3.1 milliSieverts (mSv). I’ve compiled a table to show the approximate dose delivered by some of the common radiographic studies ordered by trauma professionals. And to keep it real, I’ve calculated how much extra background radiation we would have to absorb, in units of time, to have an equivalent exposure.

Read and enjoy! Remember, doses may vary by scanner, settings, and dose reduction measures used.

Test Dose (mSv) Equivalent background
radiation
Chest x-ray 0.1 10 days
Pelvis x-ray 0.1 10 days
CT head 2 8 months
CT cervical spine 3 1 year
Plain c-spine 0.2 3 weeks
CT chest 7 2 years
CT abdomen/pelvis 10 3 years
CT T&L spine 7 2 years
Plain T&L spine 3 1 year
Millimeter wave
scanner (that hands
in the air TSA thing at
the airport)		 0.0001 15 minutes
Scatter from a chest
x-ray in trauma bay
when standing one 
meter from the
patient		 0.0002 45 minutes
Scatter from a chest
x-ray in trauma bay
when standing three 
meters from the
patient		 0.000022 6 minutes
Imaging, Resuscitation

ACS Trauma Abstract #6: Scanning Unstable Trauma Patients???

Leave a comment

If you’ve read my stuff for very long, you know I frown on sending unstable patients anywhere but to the OR. Instability tends to get worse, and that always happens at inopportune locations like hallways, elevators, and CT scanners. Imagine my surprise when I noticed an abstract being presented at the Clinical Congress of the American College of Surgeons this week suggesting that it was okay to scan hemodynamically unstable patients before “definitive therapy.”

Here’s the title:

“Computed tomography in hemodynamically abnormal thoracoabdominal trauma safely enhances surgical triage”

The devil is in the details and the language. This group from USC included all patients who were hemodynamically abnormal on arrival to the trauma bay but who normalized to SBP > 90 during the resuscitation were included.  A total of 253 of these patients were reviewed over a 9 year period, and the usual variables were analyzed (mortality, complications, hospital, ICU, and vent days, etc).

Here are the factoids:

  • Of the 253 patients studied, 45 went to straight to OR and 208 were taken to CT
  • Injury severity was identical for the two groups
  • Lengths of stay and mortality were not different, but only p values were given
  • Patients taken to CT cleared their lactic acidosis faster (12 vs 5 hours), and used a bit less plasma and significantly less blood transfusions
  • The OR group underwent more procedures (31% vs 13%), although what these were and when they were performed is not listed

Bottom line: The title of this abstract is misleading, and may fool those who don’t read the rest of the abstract. It should read:

“Computed tomography in previously hemodynamically abnormal thoracoabdominal trauma safely enhances surgical triage”

Someone who just skims through this issue of the journal may get the idea that it’s okay to scan an unstable patient. The authors are not saying this at all. If you read the conclusion carefully, you can see that the patients had to be resuscitated to a SBP > 90 before they considered taking to scan. And they did that for the majority of these patients.

The real question is, why do the scanned patients clear their lactic acidosis faster, need less blood, and undergo fewer procedures? It appears that there is some bias or selection process in play. Otherwise, why not use the magic CT scanner to make them all better?

Reference: Computed tomography in hemodynamically abnormal thoracoabdominal trauma safely enhances surgical triage. JACS 225(4S2):e175-176, 2017.

Imaging, Philosophy

If A Tree Falls In A Forest…

Leave a comment

After yesterday’s analysis of a not-so-good pan-scan vs selective-scan abstract, it’s time for a little philosophy today. There seem to be two camps in the world of initial diagnostic testing for trauma: selective scanning vs scan everything. I admit that I am one of the former. Yes, the more tests you do, the more things you will find. Some will be red herrings. Some may be true positives, but are they important? Here’s the key question:

“If a tree falls in a forest and no one is around, does it make a sound?”

There is a clinical corollary to this question in the field of trauma:

“If an injury exists but no one diagnoses it, does it make a difference (if there would be no change in treatment)?”

Here’s an example. On occasion, my colleagues want to order diagnostic studies that won’t make any clinical difference, in my opinion. A prime example is getting a chest CT after a simple blunt assault. A plain chest xray is routine, and if injuries are seen or the physical exam points to certain diagnoses, appropriate interventions should be taken. But adding a chest CT does not help. Nothing more than the usual pain management, pulmonary toilet, and an occasional chest tube will be needed, and those can be determined without the CT.

Trauma professionals need to realize that we don’t need to know absolutely every diagnosis that a patient has. Ones that need no treatment are of academic interest only, and can lead to accidental injury if we look for them too hard (radiation exposure, contrast reaction, extravasation into soft tissues to name a few). This is how we get started on the path to “defensive medicine.”

Bottom line: Think hard about every test you order. Consider what you are looking for, what you might find, and if it will change your management in any way. If it could, go ahead. But always consider the benefits versus the potential risks, or what I call the “juice to squeeze ratio.”

References:

  • George Berkeley, A Treatise Concerning the Principles of Human Knowledge, 1734, section 45.
  • paraphrased by William Fossett, Natural States, 1754.
Imaging

ACS Trauma Abstracts #5: Pan-scan vs Selective CT For Pediatric Patients

Leave a comment

In major adult blunt trauma, there are still two factions: those who pan-scan for diagnosis, and those who use CT selectively. The pan-scan proponents argue that they find everything, including things that would have been missed with selective scanning. The selective scanners argue that those things are typically not clinically significant, and radiation exposure is reduced.

Who is right? We’re still not sure. But when it comes to children, most believe that less radiation is always better. The group at USC decided to look at their experience with pan-scan vs selective imaging in blunt pediatric trauma patients, defined as those < 16 years of age. They reviewed their experience over a three year period, excluding those who had low blood pressure (<90). A total of 648 children met these criteria, and an array of variables were analyzed to try to determine “superiority.”

Here are the factoids:

  • 88% of these patients had low injury severity (ISS < 15), 567 patients
  • The low severity group who were selectively scanned had a half-day decrease in length of stay*, a quarter-day decrease in ventilator days, lower morbidity (15% vs 24%)*, and radiation exposure (8 vs 18 mSv)*, with the asterisked variables being “statistically significant”
  • The high severity also showed positive differences in decreased ICU length of stay, ventilator days, morbidity*, and radiation exposure*
  • For both pan- and selective-scanning, additional imaging led to no additional interventions in 95% of cases

Bottom line: Ugh! This is not a good abstract. It shows association, but not causation with anything but the radiation exposure calculations. Yes, if you scan less in the selective arm, there better be less exposure. But the other variables are either not clinically significant, or not defined well (i.e. morbidity).

The authors conclude that selective scanning is the way to go based on this (extremely weak) data. This is why I always recommend that you read the whole paper, not just the abstract, or in this case the whole abstract and not just the conclusion. The data, as presented in this abstract, do not support this at all.

The authors don’t say how many of these patients were very young, and how many of them actually received pan-scans. But any pediatric trauma surgeon would cringe if they read this  article. Although you may be a big believer in pan-scanning, reserve it for adults only until we have some better data. Don’t irradiate kids unnecessarily!

Reference: Selective CT imaging is superior to liberal CT imaging in the hemodynamically normal pediatric blunt trauma patient. JACS 225(4S1):562, 2017.