Glasgow Coma Scale

The Glasgow Coma Scale (GCS) was developed as a simple, objective assessment of impaired consciousness and coma, and is based on eye opening, verbal and motor responsiveness (Teasdale & Jennett 1974, 1976; Teasdale et al. 1978). It has become the most widely known and widely used scale in the assessment of level of consciousness (Foundation 2000; Hall 1997; Wade 1992).

The GCS is an observer rating scale consisting of 15 items in three basic categories: 1) motor response (6 items), 2) verbal response (5 items), and 3) eye opening (4 items). Points are awarded for the best response in each category and category scores are summed to provide a global GCS score (Sternbach 2000; Wade 1992). Total summed scores range from 3 (totally un-responsiveness) to 15 (alert, fully responsive). A total of ≤8 is used to separate coma from non-coma (Wade 1992).

Additional categorical divisions are used to differentiate patients in terms of initial severity of head injury such that GCS scores 13-15 represent mild injury, scores 9-12 represent moderate injury, and scores ≤8 represent severe injury (Sternbach 2000). The GCS is freely available, takes approximately 1 minute to administer and can be performed by all medical personnel (Oppenheim & Camins 1992). The test can be obtained at no cost at ww.trauma.org/archive/scores/gcs.html.

Table: Characteristics of the Glasgow Coma Scale

Advantages. The Glasgow Coma Scale is a simple, straightforward and very brief bedside assessment. It is the most widely used instrument in the assessment of level of consciousness. GCS scores are a significant predictor of outcome following head injury. However, the prognostic value of the GCS is increased by taking other variables into account as well, such as mechanism of injury, age, CT findings, papillary abnormalities and episodes of hypoxia and hypotension (Balestreri et al. 2004; Demetriades et al. 2004; Zafonte et al. 1996). 

Limitations. The GCS has been reported to be reliable when used by various groups of healthcare professionals regardless of the level of education or intensive care unit experience (Juarez & Lyons 1995). Nurses and general surgeons have been reported to be as consistent in their ratings as neurosurgeons (Teasdale et al. 1978). However, it has also been demonstrated that consistent ratings among inexperienced raters may also be inaccurate.  Rowley and Fielding (1991) reported that the percentage agreement between inexperienced individuals and expert raters ranged from 58.3% to 83.3%. Lower levels of accuracy were most notable in the middle ranges of the scale. Training and the implementation of standard assessment procedures are important to maintain both high levels of reliability and accuracy of evaluation. The administration of a painful stimulus appears to be somewhat controversial and there is a great deal of variability in the means and location of its application (Edwards 2001; Lowry 1999).

The GCS is most often reported as a single overall score, although the scale authors did not recommend the summary score for use in clinical practice. While the single, global score may be a convenient way to summarize data, the use of a global score may result in a loss of information that adversely affects the predictive accuracy of the GCS (Healey et al. 2003; Teasdale et al. 1983; Teoh et al. 2000). The use of a global summary score assumes that each category is equally (Teasdale et al. 1983). However, it has been reported that motor response has the greatest influence on the summary score and results are skewed toward this component (Bhatty & Kapoor 1993). Healey et al. (2003) demonstrated that the ability of the GCS score to predict survival was derived mostly from the motor response category. In addition, the summary score represents a potential 120 combinations of scores from the three GCS components collapsed into only 13 possibilities. Different combinations of motor responsiveness, verbal responsiveness and eye-opening may have different associated outcomes. Teoh et al. (2000) reported significant differences in mortality outcomes between 4 of 11 scores with multiple permutations demonstrating that individuals with the same GCS scores in varying permutations can have significantly different risks for mortality.

Perhaps the most frequently encountered limitation of the GCS is untestable components in various patient groups. Pastorek et al. (2004) reported that the ability of the patient to be evaluated on the entire GCS contributed to the prediction of global outcome measures at 6 months (Pastorek et al. 2004). Unfortunately, patients who have been intubated or sedated, those with paralysis or facial swelling, patients with hypotension, hypoxia, alcohol or illicit drug intoxication may not be able to provide responses to all categories of GCS items for reasons unrelated to head trauma (Demetriades et al. 2004; Oppenheim & Camins 1992; Rutledge et al. 1996). Murray et al. (1999), as cited in Teasdale and Murray (2000), reported that in a study of head injury patients in European centres, total assessment was possible in 61% of patients before hospital, in 77% on arrival at hospital and in 56% of patients arriving at a neurosurgical unit. It has been suggested that inability to assess using the GCS may reflect the increased and more aggressive use of intubation, ventilation and sedation (Balestreri et al. 2004; Teasdale & Murray 2000). When the GCS was developed, the initial assessment was to be undertaken approximately 6 hours after injury to allow time for stabilization of systemic problems, but prior to the initiation of interventions such as neuromuscular paralyzing agents or sedatives (Bakay & Ward 1983; Marion & Carlier 1994). Increasingly, GCS assessment is performed upon arrival at the Emergency Department and some patients may be already intubated and/or sedated by that time (Marion & Carlier 1994; Waxman et al. 1991). 

 

Summary-Glasgow Coma Scale

Interpretability: The GCS is the most familiar, most widely-used early assessment of level of consciousness. It has established categories related to the presence of coma and severity of injury. 

Acceptability: A very brief, simple observer rater scale. The application of painful stimulus is controversial. Assessment of all components is compromised by aggressive, early interventions such as intubation and sedation. 

Feasibility: The scale is simple to administer and designed for use by any health profession. Lack of experience and variability in assessment may result in inaccurate assessment. Training and standardized procedures are recommended.

 

Table: Glasgow Coma Scale Evaluation Summary

Reliability

Validity

Responsiveness

Rigor

Results

Rigor

Results

Rigor

Results

Floor/ceiling

+

++ (IO)

++

++

N/A

N/A

N/A

NOTE: +++=Excellent; ++=Adequate; +=Poor; N/A=insufficient information; TR=Test re-test; IC=Internal Consistency; IO=Interobserver; Varied (re. floor/ceiling effects; mixed results).