CHAPTER 30: GLASGOW COMA SCALE (GCS)

Description

The Glasgow Coma Scale (GCS), by Teasdale and Jennet (1974), is an interactive observation-based tool designed to describe the level of consciousness in patients with head injuries in order to facilitate the assessment and grading of brain dysfunction severity after a trauma. Developed to be a quick screen to determine if further examination is warranted, it measures three components: (1) eye opening, (2) motor, and (3) verbal response to various basic stimuli, as it is thought that the measurement of these allows the clinician to assess the function of the cerebral cortex, the upper brainstem, and the reticular activating system, where the eye-opening response measures the arousal mechanism of the brainstem; motor response; the integrity of cerebral cortex and spinal cord; and the verbal response, the integration of cerebral cortex and brainstem (Zuercher, Ummenhofer, Baltussen, & Walder, 2009). The GCS can be used as a tool to assist in the decision to intubate as well, and has been shown to be a better predictor of the need to intubate than the gag reflex (Holdgate, Ching, & Angonese, 2006). GCS scores range from 15 to 3 with lower scores indicating more severe impairment. A score of 14 to 15 is considered mild, 9 to 13 moderate, and 3 to 8 severe impairment. A modified scoring system was created based on several studies including the Canadian Computed Tomography Head Rule Study which suggest that a score of 13 be placed within the mild category of traumatic brain injury (TBI; mild, 13 to 15). However, results from a study by Mena, et al. (2011) question that decision where they plotted the odds of mortality after a TBI with GCS scores and found that a score of 13 was closer to score of 12 rather than a score of 14 (Mena et al., 2011). The following is a testing example of the eye opening response in which the person is scored as either (4) spontaneous-open with blinking at baseline, (3) to verbal stimuli, command, speech, (2) to pain only (not applied to face), and (1) no response. The GCS can be completed in less than 15 minutes.

Psychometrics

Results reporting agreement between GCS scores across a number of disciplines have shown only moderate inter-rater agreement; however, in persons with high GCS scores, inter-rater agreement has been shown to be excellent (Zuercher et al., 2009). Davis et al. (2006) suggested that “on-scene” GCS scores were strongly correlated with hospital admission and in more than 9000 non-intubated moderate to severe TBI patients a correlation coefficient of 0.67 was observed. A study of 538 persons admitted to the ICU found that those with GCS scores of 13 to 15 had a favorable outcome 93% of the time, which decreased to 83% in persons with scores of 10 to 12, 37% in scores of 7 to 9, and 10 % for scores of 3 to 6 where the mortality rate was 45% (Leitgeb et al., 2013). Those with scores of 3 to 6 found that as scores decreased mortality was 24%, 5%, and 3% with worsening GCS scores (Leitgeb et al., 2013). Finally, a study by Kevric, Jelinek, Knott, and Weiland (2011; n = 217) found that the GCS was strongly positively correlated with the Full Outline of Unresponsiveness Scale (FOUR) among 2 raters (r = 0.87 and r = 0.87); however, the inter-rater reliability for total FOUR Scale was superior to that of the GCS (0.76 and 0.59).

Advantages

The GCS is a relatively quick cognitive outcome measure that can be completed in less than 15 minutes and requires no special training or certifications. There is a good amount of research in support of its use in clinical practice and is considered by some to be a gold standard assessment. The GCS is also a component of several larger assessments such as the Acute Physiology and Chronic Health Evaluation II score, the (Revised) Trauma Score, the Trauma and Injury Severity Score, and the Circulation, Respiration, Abdomen, Motor, Speech Scale, demonstrating the widespread adoption of the scale (Majerus, Gill-Thwaites, Andrews, & Laureys, 2005). The Institute of Neurological Sciences and the Coma Science Group maintain websites devoted to the scale where one can obtain relevant information as well as downloads.

Disadvantages

Bazarian, Eirich, and Salhanick (2003) suggest that GCS has poor discriminant ability among those with scores in the moderate range. In addition, inter-rater reliability has been shown to be low for the motor component in some studies. Others have suggested that due to its ease of use, misinterpretations have occurred whereas others have argued that the application of painful stimuli (i.e., peripheral vs central) to elicit a particular response remains obscure and ill defined (McLernon, 2014). Another limitation of the scale is the fact that the GCS assesses verbal response; therefore, it is difficult to apply to a number of patient populations. However, a study found that many clinicians had a poor understanding of this, with only 46% agreeing with the statement that the GCS cannot be used on intubated patients (Kevric et al., 2011).

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