Review of: Sochor M, Althoff S, Bose D, et al. Glass intact assures safe cervical spine protocol. J Emerg Med. 2012 Dec 20, Epub ahead of print.
The Science: This is a retrospective cohort analysis from a U.S. National Highway Traffic Safety Administration database (National Automotive Sampling System Crashworthiness Data System) that examined crashes from 1998 to 2008. Investigators were interested in vehicle window integrity and the relationship to restrained, front seat (driver and passenger) occupants in motor vehicle crashes (MVCs) that required vehicles to be towed from the scene. Using only objective data, investigators hypothesized that if patients met certain criteria: age 16-60, no damage to the vehicle’s windows occurred, no airbags were deployed, and front seat occupants were restrained—that a patient isn't likely to have a cervical spine (C-spine) fracture. Investigators included more than 14,000 patients in the analysis, and using a 2x2 contingency table for analysis, concluded the test had a specificity (the probability of a positive test actually being positive) of 99%, a sensitivity (the probability of a negative test actually being negative) of 54%, and a predictive value negative (proportion of true negative tests) of 99.9%. This means that patients who met all the criteria were almost 100% not likely to have C-spine injury.
Medic Marshall: I’d like to start off by congratulating these investigators on this study; it is truly a simple, yet remarkable study that will contribute to the advancement of EMS care. With that said, let’s examine this study a little further.
First of all, it should be noted that this study pulled data from a national database, which may have a tendency to skew the results in this study, but I wouldn’t go so far as to say it would skew them so dramatically one should discredit the results. As the authors state, a prospective study would definitely help to validate the results herein. I do believe this would not be too much of a tremendous undertaking for any aspiring EMS researchers out there.
Secondly, studies like this, along with NEXUS and the Canadian C-spine Rule, are starting to show cervical injuries in MVCs are actually fairly rare. More often than not, we're immobilizing patients that probably don’t require it. Investigators in the study pointed out that immobilizing patients are not completely without their risks as well. For all the EMS practitioners who have been placed on a long backboard in school know how uncomfortable—despite padding—they are. So again, the less we need to place people on a hard piece of plastic and make their life a little more comfortable, the better.
Finally, what I think is so great about this study is its pure objectiveness. In a short, simple list of criteria, EMS could have a tool at their hands that could broaden the number of patients who are made more comfortable by not boarding them. And because of the objectiveness of the study, we can also capture those intoxicated patients who are forced onto backboards, simply because they were under the influence of alcohol.
At the end of the day, I would encourage anyone interested in incorporating this tool into their repertoire to push those who do research, especially medical directors, to examine this study and conduct their own prospective trials to eventually help make this standard practice.
Doc Wesley: Every day, more evidence accumulates indicating that we are potentially creating more harm than good with spinal immobilization. This study, while having some limitations, offers yet another tool that may allow us to better determine the likelihood of an unstable spinal injury.
The primary limitation of the study is that it's retrospective and only cars that had to be towed from the scene are included in the national database. However, it's reasonable to conjecture that cars that are drivable after the accident would have sustained less damage and subjected the occupant to less energy.
Although most of us have already adopted the Canadian and NEXUS criteria for selective spinal immobilization, two groups of patients are frequently excluded: intoxicated patients and those with distracting injuries that result in erring on the side of spinal immobilization. Using the GLASS criteria, they could be included and avoid the unnecessary pain and suffering of the backboard.
Although several professional organizations continue to debate the role of spinal immobilization in EMS, I have already adopted an aggressive stance. Those that might benefit from immobilization are transported only with a cervical collar (C-collar) and no backboard. It's time we recognized that backboards can harm patients and should be relegated to extrication only.
Background: Selective cervical spine immobilization performed by Emergency Medical Services (EMS) is being utilized with increasing frequency. These protocols, although very sensitive, still include subjective data such as “mild cervical discomfort.” The aim of this study is to create an objective clinical decision rule that would enhance the selective approach for cervical spine immobilization in patients aged 16–60 years.
Study Objective: It is hypothesized that, in a motor vehicle crash, the integrity of the involved vehicle’s glass window and airbag status is an excellent objective measure for the amount of energy a vehicle occupant has experienced during the crash. GLass intact Assures Safe Spine (GLASS) is an easy and objective method for evaluation of the need for prehospital cervical spine immobilization.
Methods: A retrospective cohort study was performed with sample motor vehicle crash cases to evaluate the performance of the GLASS rule. The National Accident Sampling System-Crashworthiness Data System (NASS-CDS) was utilized to investigate tow-away motor vehicle crashes, including their glass damage characteristics and occupant injury outcomes, over an 11-year period (1998–2008). Sample occupant cases selected for this study were patients aged 16–60 years, who were belt-restrained front seat occupants involved in a crash with no airbag deployment, and no glass damage before the crash.
Results: A total of 14,191 occupants involved in motor vehicle crashes were evaluated in this analysis. The results showed that the sensitivity of the GLASS rule was 95.20% (95% confidence interval [CI] 91.45–98.95%), the specificity was 54.27% (95% CI 53.44–55.09%), and the negative predictive value was 99.92% (95% CI 99.86–99.98%).
Conclusion: The GLASS rule presents the possibility of a novel, more objective tool for cervical spine clearance. Prospective evaluation is required to further evaluate the validity of this clinical decision rule.