Glasgow Coma Scale Gets an Eye-Opening Update

Damian McNamara

April 19, 2018

Working with a developer of the original Glasgow Coma Scale (GCS), researchers have found that adding pupil response to the GCS more accurately predicts prognosis after traumatic brain injury, including the likelihood of death, than either measure alone.

Because previous research suggested that the GCS score and pupil reaction independently provide the most information about head injury prognosis, researchers put them together to create the GCS-pupil response (GCS-P).

Pooling health records from two large studies with more than 15,000 patients, they found the GCS-P would have improved doctors' ability to predict patient prognosis condition in the 6 months after a brain injury.

For example, loss of pupil reactivity was associated with an increase in mortality rate of 16% when both pupils reacted, 38% when only one reacted, and 59% when neither pupil reacted.

They assessed health records from the Corticosteroid Randomisation After Significant Head Injury (CRASH) and International Mission for Prognosis and Clinical Trials in TBI (IMPACT) databases ( Lancet. 2004;364:1321-1328; J Neurotrauma. 2007;24:239-250).

"The idea came from Graham [Teasdale]," lead author, Paul M. Brennan, MBBChir, PhD, from the Centre for Clinical Brain Sciences at Edinburgh University in the United Kingdom, told Medscape Medical News.

"We had been working on other developments around the GCS, and he showed me a piece of graph paper he'd kept from the original work back in the 70s, where he'd sketched out the impact of pupil reactivity on GCS. Forty years later he thought it was a question worth pursuing."

The study was published online April 10 in the Journal of Neurosurgery.

Greater Degree of Accuracy

Other researchers have amended the GCS over the years. One version used additional information about memory to expand discrimination among patients with mild head injuries, for example. Others focused on patients with severe brain injury, adding different brainstem features to the GCS calculation.

"Surprisingly, in studies in which predictive performance has been compared, the extra prognostic yield above the GCS score provided by these additional sources usually has not been significant and, with the exception of pupil response, the value of their contributions has been questioned," Brennan and coauthors write.

Although other tools that assess head injury exist, simplicity is key, he added.

"The other, more complicated tools are simply not widely used in clinical practice. GCS has been the gold standard for assessing the severity of head injury. By adding in pupil reactivity and the other components in the prognostic chart, we demonstrated that we added value to the assessment and that the accuracy of the tool was similar to the more complicated models."

In the current study, the researchers examined different methods for combining the GCS and the pupil response to gauge mortality or an unfavorable outcome, such as a vegetative state or severe disability following acute head injury.

After excluding patients with incomplete data, they assessed 15,900 patients in a pooled analysis.  

Brennan and colleagues then created a Pupil Reactivity Score (PRS) based on the number of nonreactive pupils. If both pupils are unreactive, the score is 2; if only one pupil is unreactive, the score is 1; and if both pupils reacted, the score is 0. Next, they obtained a combined GCS-P score for each patient by simply subtracting the PRS from the GCS total score. GCS-P values range from 1 to 15.

Brennan shared a hypothetical example.

"Imagine that you are asked to assess a patient who has been ejected from the passenger seat of a car at high velocity. They make no eye, verbal, or motor movements spontaneously, nor in response to your spoken requests. When stimulated their eyes do not open, they make only incomprehensible sounds, and their arms abnormally flex. This patient can be scored as E1V2M3 using the GCS, giving a sum score of 6," he said.

Neither pupil is reactive to light, generating a PRS score of 2. In this case, the GCS-P is then 6 minus 2 or 4 points. "With a GCS 6 there is a 29% chance of death at 6 months. When the pupil reactivity and GCS are combined to give a GCS-P, the mortality increases to 39%."

Brennan was "not surprised that pupil reactivity added value to the assessment but surprised how simply the GCS and pupil score could be incorporated into a single metric, and how much more information this gives about prognosis."

Outcomes Prediction

Similar to the increased mortality risk predicted by the GCS-P, poor outcomes also increased from 31% when both pupils reacted to light, to 63% when one reacted, and to 79% when neither pupil reacted.

"Pupil reactivity is already assessed in much of clinical practice. For those people who already do it, the new metrics from GCS-P offer clinicians a greater degree of accuracy with which to discuss things with patients and to make clinical decisions about outcome. For people who do not regularly assess pupil reactivity, this will serve as a prompt to perform this important test," he said.

The new scale also carries implications for research, potentially helping to better stratify patients for clinical studies, he added.

"Our research, presented in the papers, indicates that the addition of the pupil component adds value across the GCS, but it will be most useful for those with the lower GCS scores," he said. "These are the more severely head-injured patients and are most likely to have altered pupil reactivity." 

GCS scoring is not always linear regarding severity — a score of 4 is sometimes associated with an increase in mortality and unfavorable outcome compared with a GCS score of 3 (Injury. 2016;47:1879-1885).

The reason for this paradoxical finding is unclear, the researchers noted, adding that it disappears with GCS-PR scores from 1 to 4.

The researchers also offered a caveat along with their findings. "The combined GCS-P is not intended to replace the role of separate assessment and reporting of each component of the Glasgow Coma Scale and pupil response in the care of individual patients. This remains the most informative way of determining and sharing a 'picture' of the patient's condition and how it may be changing."

The researchers are calling on the clinical community to assess and evaluate the role of the GCS-P.

In the meantime, Brennan and colleagues plan to validate their findings in additional populations.

"There are some big clinical trials about to report in head injury and it will be important to validate our findings in this contemporary population," he said. Examples include the prospective Collaboration European NeuroTrauma Effectiveness Research in TBI (CENTER-TBI) and the Transforming Research and Clinical Knowledge in Traumatic Brain Injury (TRACK-TBI) trials.

Adoption Highly Likely

Commenting on the findings for Medscape Medical News, Chad Miller, MD, medical director of neurocritical care at Ohio Health Neuroscience Center and a neurologist at Ohio Health Riverside Methodist Hospital in Columbus,  said that "the GCS retained popularity in part due to its simplicity of use, consistency of assessment, dependence upon highly impactful variables — level of alertness, speech, movement — and capacity to be expressed in a numerical scale familiar to healthcare professionals."

However, he added, the scale does have some shortcomings. It lacks detail, and components of the GCS are difficult to assess or are not relevant to certain patient populations. 

Likewise, he said, the presence or absence of pupillary reactivity has a strong correlation to severity of brain injury and outcome across a variety of neurologic conditions.

"The authors found that creating a linear score, with a range of 1 to 15, combining both the GCS and pupillary exam resulted in a better estimation of survival after brain injury," he said.

"The modification to the GCS-Pupils Score allowed for reduction of the conventional GCS score as a result of loss of unilateral or bilateral pupillary response. This simple change better differentiated survival after brain injury, particularly for patients with GCS scores in the range of severe traumatic brain injury.

"As opposed to previously proposed brain injury severity scales, whose use was limited by their complexity or unfamiliarity of the user, the GCS-Pupils Score has the advantage of being easy and quick to utilize and is based upon a recognized standard in neurological assessment," Miller added.

"The scale proposed in this study has a high likelihood of adoption by the general medical community and is an improvement upon a time-tested standard for evaluation of patients with brain injury." 

Better Together

Also commenting, Brian K. Lebowitz, PhD, ABPP-CN, director of neuropsychology training and associate professor of clinical neurology at Stony Brook Medicine in New York, told Medscape Medical News that the simplicity of subtracting the number of nonreactive pupils from a patient's total GCS score and coming up with a more accurate predictor of mortality and adverse outcomes than either measure alone is encouraging.

"[T]he prognostic information provided by this combined score was almost as good as that provided by more complicated methods that are less favored in clinical settings.

"The utility of the measure appears to be greater for more severe injuries involving lower GCS scores — particularly those involving a GCS of 3, as the metric lowers the effective floor to a score of 1," Lebowitz said.

However, he noted the authors' caution that "continued appreciation and reporting of each GCS component, as well as the use of other assessment methods, will continue to be necessary."

The Muriel Cooke Bequest to the University of Glasgow financially supported the study. Brennan, Miller, and Lebowitz have disclosed no relevant financial relationships.

J Neurosurg. Published online April 10, 2018. Full text

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