Glasgow Outcome Scale/Extended Glasgow Coma Scale

The Glasgow Outcome Scale (GOS) is a practical index of social outcome following head injury designed to complement the Glasgow Coma Scale as the basis of a predictive system (Jennett & Bond 1975). It is a simple, hierarchical rating scale with a limited number of broad categories. The scale focuses on how head injury had affected function in major life areas and is not intended to provide detailed information on specific deficits (Wilson et al. 1998). Individuals within any single outcome category represent a range of abilities (Jennett & Bond 1975).

Patients are assigned to one of five possible outcome categories: 1) death, 2) persistent vegetative state, 3) severe disability, 4) moderate disability, and 5) good recovery (Jennett & Bond 1975). In 1981, a revision to the scale was proposed to better classify patients who had regained consciousness (Jennett et al. 1981). In the Extended Glasgow Outcome Scale (GOSE), each of the three categories applicable to conscious patients are subdivided into an upper and lower band resulting in eight possible categories. GOS ratings can be derived from the GOSE by collapsing these subdivisions (Wilson et al. 2000).

The assignment of an individual to an outcome category should be based on the results of a structured interview focused on social and personal functional ability (Jennett et al. 1981). The final rating is based on the lowest category of outcome indication in the interview (Wilson et al. 2000). The GOS and GOSE can be accessed for no cost at www.tbi-impact.org/cde/mod_templates/12_F_01_GOSE.pdf.

Table: Characteristics of the Glasgow Outcome Scale and Extended Version

Advantages. The GOS is the most widely used and accepted measure of outcome following head injury (Wade 1992). It has been adopted widely for use in clinical trials (Hellawell et al. 2000; Wade 1992; Wilson et al. 2000). It is a simple, reliable means of describing recovery (Jennett et al. 1981) that is quick to administer, broadly applicable and has clinically relevant categories (Wilson et al. 2000).

Structured interviews and guidelines for their administration are available for the GOS and GOSE (Wilson et al. 1998). Each interview incorporates a way to include information regarding pre-injury status, thereby providing a means for determining the effect of the sequelae of head injury on outcome, separate from the effects of pre-existing conditions or circumstances (Pettigrew et al. 1998; Wilson et al. 1998). While use of the structured interview has increased the reliability of postal and telephone administration, face-to face interview remain the preferred method to determine a GOS rating (Wilson et al. 2002).

Limitations. The GOS provides an overall assessment of outcome and does not provide detailed information with regard to specific disabilities or handicaps. Categories are broad and the scale does not reflect subtle improvements in functional status of an individual (Pettigrew et al. 1998). Individuals may achieve considerable improvement in ability, but not change outcome category (Brooks et al. 1986). The GOS rating was intended primarily to provide an overall summary of outcome and facilitate comparison, not to describe specific areas of dysfunction (Pettigrew et al. 1998). In addition, GOS outcome categories are often expressed as a dichotomy: poor or unfavourable outcome versus independence or favourable outcome. This results in a loss of information and low sensitivity (Teasdale et al. 1998).

Originally, GOS categories were described according to a range of features, but specific criteria were not defined for each of the different outcomes. This lack of clarity may have had a negative impact on scale reliability by introducing an element of subjectivity on the part of the rater (Maas et al. 1983; Teasdale et al. 1998). In addition, attempts to increase the sensitivity of the GOS by subdividing the upper three categories in an upper and lower band was associated with decreased consistency in category assignments (Maas et al. 1983). However, the structured interview and guidelines created by Wilson et al. (1998) have alleviated much of the difficulty surrounding ambiguous assignment criteria.

 

Summary-Glasgow Outcome Scale

Interpretability: The GOS is widely used and accepted. The GOS provides an overall assessment suitable for the comparison of outcomes at the group level.

Acceptability: The brevity and simplicity of the GOS facilitates patient compliance. The GOS has been studied for use by telephone and mail administration. Structured interviews improve the reliability of administration by these methods.

Feasibility: The GOS can be used by professionals from various backgrounds and does not require any physical, psychiatric or neurologic examination. It is well-suited to busy clinical settings and large scale research trials.

 

Table: Glasgow Outcome Scale/Extended Evaluation Summary

Reliability

Validity

Responsiveness

Rigor

Results

Rigor

Results

Rigor

Results

Floor/ceiling

+

++(TR)

++(IO)

++

+++

+

+(p-values only)

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).