Tag Archives: ct scan

EAST 2017 #1: Accuracy of CT Scans Done Outside The Trauma Center

Imaging prior to transfer to a trauma center has been the subject of debate for years. The focus has primarily been on the necessity of these scans, and the sheer numbers that are done. For the most part, the discussion has been driven by the potential for radiation exposure.

This paper, from the University of Oklahoma, takes a different approach. The authors looked at the accuracy and adequacy of imaging performed prior to transfer to their Level I trauma center.

Patients were enrolled prospectively over an 8 month period in 2012. Outside images were interpreted by a single radiologist who was blinded to the outside interpretation.  If images were repeated, they were compared to the first scan, and the reason for the redo was noted.

Here are the factoids:

  • 235 consecutive transfer patients were enrolled, and 203 who had at least one CT scan were included in the final dataset
  • 76% of these patients had additional imaging performed once they arrived at the trauma center
  • Reasons for additional images were insufficient workup (76%) and technical inadequacy (31%)
  • Missed injuries were detected on outside CT scans 49% of the time, and the majority of them (90%) were deemed clinically significant
  • Missed injuries on a repeated scan were present in 54% of patients, and 76% were clinically significant
  • Overall, 73% of images (either outside or repeat) contained additional injuries

Bottom line: This is a new approach to assessing the value of outside imaging prior to transfer to a trauma center. I have always recommended that trauma centers work with their referral partners to assure them we don’t need them to do the workup for us. I encourage them to obtain only what they need to decide if they can keep the patient. But once they find anything that they cannot treat, stop all workup and prepare to transfer.

Questions/comments for the authors/presenters:

  • Why did you use such an old dataset?
  • Is this a prospective enrollment/retrospective analysis study designed to use an existing, old dataset?
  • How did you decide that outside imaging represented an inadequate workup? Do you have a diagnostic imaging guideline that you follow?
  • What are the credentials for your trauma radiologist?
  • How did you determine that a missed injury was clinically significant? Be sure to provide a list and explanation during your presentation.
  • Be sure to separate out missed injuries seen on the original CT from new missed injuries seen on the repeat scan.
  • Congratulations on looking at an old problem in a new way!

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

Related posts:

Reference: Adequacy and accuracy of non-tertiary trauma center computed tomography: what are we missing? Paper #7, EAST 2017.

Pan Scanning for Elderly Falls?

The last abstract for the Clinical Congress of the American College of Surgeons that I will review deals with doing a so-called “pan-scan” for ground level falls. Apparently, patients at this center have been pan-scanned for years, and they wanted to determine if it was appropriate.

This was a retrospective trauma registry review of 9 years worth of ground level falls. Patients were divided into young (18-54 years) and old (55+ years) groups. They were included in the study if they received a pan-scan.

Here are the factoids:

  • Hospital admission rates (95%) and ICU admission rates (48%) were the same for young and old
  • ISS was a little higher in the older group (9 vs 12)
  • Here are the incidence and type of injuries detected:
Young (n=328) Old (n=257)
TBI 35% 40%
C-spine 2% 2%
Blunt Cereb-vasc inj * 20% 31%
Pneumothorax 14% 15%
Abdominal injury 4% 2%
Mortality * 3% 11%

 * = statistically significant

Bottom line: There is an ongoing argument, still, regarding pan-scan vs selective scanning. The pan-scanners argue that the increased risk (much of which is delayed or intangible) is worth the extra information. This study shows that the authors did not find much difference in injury diagnosis in young vs elderly patients, with the exception of blunt cerebrovascular injury.

Most elderly patients who fall sustain injuries to the head, spine (all of it), extremities and hips. The torso is largely spared, with the exception of ribs. In my opinion, chest CT is only for identification of aortic injury, which just can’t happen from falling over. Or even down stairs. And solid organ injury is also rare in this group.

Although the future risk from radiation in an elderly patient is probably low, the risk from the IV contrast needed to see the aorta or solid organs is significant in this group. And keep in mind the dangers of screening for a low probability diagnosis. You may find something that prompts invasive and potentially more dangerous investigations of something that may never have caused a problem!

I recommend selective scanning of the head and cervical spine (if not clinically clearable), and selective conventional imaging of any other suspicious areas. If additional detail of the thoracic and/or lumbar spine are needed, specific spine CT imaging should be used without contrast.

Related posts:

Reference: Pan-scanning for ground level falls in the elderly: really? ACS Surgical Forum, trauma abstracts, 2016.

The CT Crystal Ball – Part 2

Yesterday, I wrote about a study that looked at a CT scan-derived index that promised to predict complications and mortality based on the waist-hip ratio. It was actually a very good one. But there is another abstract being presented at the American College of Surgeons Clinical Congress this week that promises miracles from the CT scanner as well.

This next abstract looks at muscle mass in trauma patients, as measured by CT scan. Specifically, the authors measured the density of the psoas muscle by determining its cross-sectional area and its density in Hounsfeld units. They then looked at the relationship between this and 90 day mortality, complications, and disposition location.

Really? Well, here are the factoids:

  • The study involved only 152 patients age 45+ from the year 2008
  • Median ISS was only 9
  • Patients with the lowest psoas cross-sectional area had an associated significantly higher death rate
  • Those with lowest psoas density had an associated increase in complications, dependency on discharge, and mortality
  • The authors suggest that these measurements could aid in patients who would benefit from aggressive nutritional support and physical therapy, and could aid in discharge planning

Bottom line: Very different from yesterday’s abstract. This one has no grounding in prior research. It appears to be one that was just dreamed up from nowhere. And it is truly an association study. No causality can or should be inferred.

There were only 152 patients studied. From 2008. Why? Why didn’t the authors use a more contemporary dataset? There is something weird going on behind the scenes. Is this an old study that was forgotten, and is just now being conveniently dusted off for analysis and submission? A power analysis to find out how many patients should be reviewed is not possible, so it is important to err on the high side. Not just 152 patients.

If you were to just read the abstract and especially the conclusions, you really might get the wrong idea. This is a study that will not see it’s day in any journal. Read and learn from it. But don’t duplicate it!

Related post:

Reference: Computed tomography-measured psoas density predicts complications, discharge location, and mortality in trauma patients. ACS Scientific Forum, trauma abstracts, 2016.

 

 

Using The CT Scan As A Crystal Ball For Trauma?

Two abstracts that are being presented at the American College of Surgeons Clinical Congress this week use CT scans to predict interesting things. They are things that you would not think a CT scanner should be able to do.

So can we use arcane measurements of things found on CT scan to make accurate predictions about our patients? Sure, if we see very low density bubbles (free air) in the abdomen, it’s pretty likely that some kind of abdominal catastrophe has occurred. Or if their is a large amount of high density fluid (blood) in the left chest after a stab wound, the patient will probably require a chest tube.

But what about other measurements that wouldn’t seem to be related to anything? Could we have found a magic crystal ball here, or is it just wishful thinking?

The first abstract evaluated the ability of the waist to hip ratio (WHR) to predict outcomes after trauma. Obviously, this is the width of the waist divided by the width of the body at the hips.

waist-hips-ratio1

Here are the factoids for this study:

  • 555 patients were analyzed retrospectively over 1 year at a Level I trauma center.
  • In-hospital complications and death were specifically analyzed
  • Using a receiver operating characteristic curve, the authors determined that a magic ratio of 1 was the best predictor
  • Complications were significantly higher in the group with WHR>1 (50% vs 19%) as was mortality (17% vs 7%)
  • Regression analysis showed that patients with WHR>1 were 4x more likely to have a complication and 3x more likely to die
  • WHR was only weakly correlated with BMI

Bottom line: WTF? How can this be, you ask? Just because your patient is a bit “fusiform” in shape, they have a rougher time after trauma? Well, in this case there may actually be some basis for the findings. There are thousands of articles in the literature that have identified that this shape actually is associated with higher complications and mortality in general. And there are already some published trauma papers that have confirmed this association. Interestingly, the BMI was less predictive that the WHR in this study, so this may be a better surrogate measure for obesity.

The number of patients enrolled is reasonable, and the statistics look sound (for just being an abstract). So there may be something here. However, before you start using the “measure tool” on your CT console on every trauma patient, wait for the confirmatory prospective studies to come along. 

Tomorrow, a look at a not-so-good study of this type, looking at an even more arcane metric on the CT scan.

Reference: Computed tomorgraphy-measured waist to hip ratio: a reliable predictor of outcomes after trauma. ACS Scientific Forum, trauma abstracts, 2016.

ED Use of CT – Everyone Does It Differently

There is tremendous variability in ordering imaging in trauma patients. To some degree, this is due to the dearth of standards pertaining to radiographic imaging, at least in trauma. And when standards do exist, trauma professionals are not very good at adhering to them. We’d rather do it our way. Or the way we were trained to do it.

The group at Jamaica Hospital in Queens, NY quantified some of those differences, studying ordering patterns of trauma surgeons (TS), emergency physicians (EP), and surgery chief residents (CR). Unfortunately, they then tried to draw some interesting conclusions, which I’ll discuss at the end.

They reviewed all blunt trauma activations over a 6 month period at their urban trauma center. At the end of each trauma activation, each of the three physician groups wrote imaging orders, but only the trauma surgeons’ were submitted. Missed injuries were defined as any that would not have been found based on each provider group’s orders. Extremity injuries, and those found on physical exam or plain imaging were excluded.

Here are the factoids:

  • The authors do not state how many patients they saw in this period, but by extrapolation it appears to be about 250
  • Trauma surgeons ordered significantly more studies (1,012) than the EPs (882) or CRs (884)
  • This resulted in essentially a “pan-scan” in 78%, 64%, and 69%, respectively
  • Radiation exposure was said to be the same for all groups (18 vs 13 vs 15 mSv) [I’m having a hard time buying this]
  • But cost was higher in the trauma surgeon group ($344 vs $267 vs $292) [Huh? Is this only the electric bill for the CT scanner? Very low, IMHO]
  • And the trauma surgeons had a missed injury rate of only 1%, vs 11% for EPs and 7% for CRs [Wow!]

Bottom line: Sorry, I just can’t believe these results. There are a lot of things left unsaid in this poster. What were all these missed injuries? What magical CT scan that only the trauma surgeons ordered actually picked them up? And probably most importantly, were they clinically significant? A small hematoma somewhere doesn’t make a difference (see the “tree falls in a forest” post below).

It looks to me like the authors wanted to justify their use of pan-scan, and push their emergency physicians to follow suit. Unfortunately, this is a poster presentation, meaning that there will be limited opportunity to question the authors about the specifics.

The debate regarding pan-scan vs selective imaging is an active one. The evidence is definitely not in yet. While we sort it out, the best path is to develop a reasonable imaging practice guideline based on the literature, where available. Some areas such as head and cervical spine CT have been worked out fairly well. Then fill in the blanks and encourage all trauma professionals in your hospital to follow them. There is great value in adhering to good guidelines, even when there are blanks in our knowledge.

Related posts:

Reference: Variability in computed tomography imaging of trauma patients among emergency department physicians and trauma surgeons with respect to missed injuries, radiation exposure and cost. AAST 2016, Poster #75.