All posts by TheTraumaPro

How Not To Write An Abstract

I always encourage people to be careful when reading abstracts. Read the entire article, I say. Here’s a perfect example of why this is true.

Artificial blood products have been one of the holy grails of trauma for decades. Typically, a new one is developed, shows promise, then flames out for one reason or another. MP40X is yet another hemoglobin molecule that has been shown to improve tissue oxygen delivery. A multi-center clinical study was designed to look at clinical outcomes in real trauma patients. The study involved 38 hospitals, and was placebo controlled. Only patients in hemorrhagic shock with an elevated serum lactate were enrolled. The primary outcome was survival at 28 days.

Here are the factoids:

  • 313 patients were successfully studied over 17 months, with nearly equal numbers of MP40X vs normal saline controls
  • The two groups were well-matched for the usual demographics
  • Mortality for MP40X was 12% vs 14% for controls (not significant)
  • Serious adverse events were the same (36% vs 37%)
  • 57% of MP40X patients were alive at 28 days vs 50% of controls (not significant)
  • Ventilator-free days, hospital-free days, and organ failure was the same between the groups

However, the authors conclude:

While there were promising trends to suggest a potential for improved outcomes, the study was underpowered to confirm the efficacy of MP40X in trauma hemorrhage.”

Bottom line: When someone designs a study, especially a multi-center study that lots of people will spend their time and money on, the investigators are responsible for doing it right. This includes trying to estimate how many patients are needed to have a chance of showing a significant difference. Granted, this may be somewhat difficult with a new product or drug, but at least estimate on the high side.

This study abstract blames the lack of results on not having enough subjects. If that is truly the case, the reasons for underpowering it should be explained in the abstract. Otherwise, it just looks like they are making excuses and raise hopes for an ineffective product.

Reference:Effects of MP40X, an oxygen therapeutic, on clinical outcomes in trauma patients with hemorrhagic shock: a Phase IIb multi-center randomized placebo-controlled trial. AAST 2013, Paper 15.

A hat tip to the Skeptical Scalpel for bringing this paper to my attention.

Pet Peeve: “High Index of Suspicion”

How often have you heard this phrase in a talk or seen it in a print article:

“Maintain a high index of suspicion”

What does this mean??? It’s been popping up in our work for at least the last 20 years. And to me, it’s meaningless.

An index is a number, usually mathematically derived in some way. Yet whenever I see or hear this phrase, it doesn’t really apply to anything that is quantifiable. What the author is really referring to is “a high level of suspicion”, not an index. 

This term has become a catch-all to caution the reader or listener to think about a (usually) less common diagnostic possibility. As trauma professionals, we are advised to do this about so many things, it really has become sad and meaningless.

Bottom line: Don’t use this phrase in your presentations or your writing. It’s stupid. And feel free to chide any of your colleagues who do.

Reference: High index of suspicion. Ann Thoracic Surg 64:291-292, 1997.

AAST 2013: Screening For Blunt Cerebrovascular Injury

Blunt cerebrovascular injury (BCVI) is one of those low incidence, high consequence injuries like traumatic aortic rupture. Unfortunately, BCVI has gotten less attention and is less frequently screened for during trauma evaluation. There are two choices of screening criteria: digital subtraction angiography (DSA) or CT angiography (CTA). Previous work by the UT Memphis team showed that the sensitivity of evaluation by 32-slice CT angio is only 51%.

Although DSA has been considered the gold standard, there are several drawbacks. First, it is invasive and has its own collection of complications, including stroke. And it is not available at all centers, and even in those that have it, it is frequently a limited resource. Current 32-slice CTA risks missing significant injuries, which can also lead to stroke.

The UT Memphis team has now followed up their 32-slice work with a new study evaluating 64 slice scanners. Here are the factoids:

  • Over a one year period, 594 patients underwent both CTA and DSA for evaluation of BCVI
  • 128 patients had 163 injured vessels (!), 61% carotid and 39% vertebral
  • 5 DSA complications occurred (1%): 3 puncture site hematomas and 2 iatrogenic dissections
  • 64-slice CTA had an improved sensitivity of 68%

Bottom line: CT angiography for blunt cerebrovascular injury is following the same trajectory that it did for evaluating traumatic aortic injury. As the resolution of the scans improves, our diagnostic accuracy does the same. CTA using a 64-slice scanner will now begin to displace digital subtraction angiography due to its readier availability and low complication rate. 

BUT, the most important part of the process is that the trauma professional needs to use solid criteria to make the decision to use it!

Related posts:

Reference: Blunt cerebrovascular injury screening with 64-channel multidetector computed tomography: more slices finally cut it. AAST 2013, Paper 13.

AAST 2013: Nonselective Angiography For Splenic Injury

Angiography is yet another tool for use in the management of splenic injury. Over the past decade, it has helped improved splenic salvage rates into the mid-90% range. Angio can be used selectively (for very specific indications) or nonselectively (routinely).

The University of Tennesse – Memphis tried to examine whether there was any benefit to more frequent, nonselective use of this tool. They analyzed data in the National Trauma Data Bank (NTDB). They excluded patients with early splenectomy (within 6 hours). Selective vs nonselective use was determined by looking at the percentage of patients from a specific hospital that underwent the procedure. Low or no use hospitals used it from 0-20% of the time, and high use hospitals used it in >20% of cases. 

Here are the factoids:

  • 7412 records were analyzed
  • There was no difference in splenic salvage rates in low vs high angio use centers
  • Higher overall injury severity and AIS 5 for spleen was associated with higher delayed splenectomy

Bottom line: Not a very enlightening analysis. The researchers equated high utilization with non-selective utilization, which is a big flaw. The numbers are large, but the underlying assumptions are weak. And we already knew that higher injury severity and higher grade spleen injury equals higher splenectomy rate.

I recommend that any center that uses angiography as an adjunct to management of splenic injury to have specific indications (grade, degree of hemoperitoneum, CT contrast extravasation, etc). This ensures uniform use of this tool, and helps optimize the risk:benefit ratio to improve patient safety.

Related posts:

Reference: Are we lemmings?: Nonselective use of angiography provides no benefit in high-grade splenic injury. AAST 2013, Paper 12.

AAST 2013: Seizure Prophylaxis After TBI

The Brain Trauma Foundation has an extensive set of guidelines for the management of traumatic brain injury. One of these involves the routine administration of anti-seizure prophylaxis. The risk of seizure after TBI is higher than in the general population, and a high risk group has been identified (GCS<10, depressed skull fracture, cortical contusion, subdural / epidural / intracerebral hematoma, penetrating injury, or seizure within 24 hours.

This guideline showed that there was no data to support a recommendation with the highest degree of evidence, but it did suggest that anti-seizure meds decreased the incidence of early seizures (within 7 days), but these seizures had no effect on outcome. This meant that you might consider giving phenytoin, but there was always the risk associated with giving any new medication, and no real benefit to the outcome. This is one reason why the guideline is applied inconsistently by trauma professionals.

Researchers at the University of Florida – Jacksonville will be presenting a paper at AAST 2013 further questioning the advisability of this guideline. They retrospectively reviewed 93 patients who were admitted to their hospital for at least 7 days with severe blunt TBI. They split the patients into two groups, a control group (43 patients) who did not receive phenytoin and a study group (50 patients) who had therapeutic levels.

Here are the factoids:

  • More seizures occurred in the phenytoin group (4% vs 0%)
  • Mortality was the same (8% vs 7%)
  • Discharge disposition (home vs rehab) was the same
  • Hospital length of stay was longer in the prophylaxis patients (36 vs 25 days)
  • Glasgow Outcome Scale was worse in the phenytoin group (2.9 vs 3.4)

Bottom line: Don’t pay much attention to this study. It’s very small, making the quality of the results pretty shaky. There is no comment on matching other injuries that might account for a difference in length of stay. And is this the proper way to find a difference in Glasgow Outcome Scale, an integer value? What does 2.9 or 3.4 mean? Nothing. It has to be a 3 or a 4, no decimal point.

Although the data supporting the original Brain Trauma Foundation guideline is a bit weak, this paper does not support changing current practice. Needs more work (and more numbers).

Related post:

Reference: More Harm Than Good: Anti-seizure prophylaxis after traumatic brain injury does not decrease seizure rates but may inhibit functional recovery. AAST 2013 Paper 10.