What is the purpose and interpretation of the Glasgow Coma Scale (GCS) in assessing patients with head injuries?

The Glasgow Coma Scale (GCS): Purpose and Interpretation in Head Injury Assessment

The Glasgow Coma Scale is a standardized clinical tool designed to assess level of consciousness in patients with head injuries, with serial GCS determinations being the most valuable method for detecting neurological deterioration and predicting outcomes in traumatic brain injury patients. 1

What is the Glasgow Coma Scale?

The Glasgow Coma Scale was developed by Teasdale and Jennett in 1974 as a standardized method to:

• Facilitate reliable interobserver neurologic assessments of comatose patients
• Enable serial evaluations by relatively inexperienced providers
• Improve communication between healthcare providers on rotating shifts 1

The scale consists of three components:

1. Eye opening (scored 1-4)
2. Verbal response (scored 1-5)
3. Motor response (scored 1-6)

These components are summed to create a total score ranging from 3 (deep coma) to 15 (normal consciousness).

Primary Purpose of GCS in Head Injury Assessment

The GCS serves several critical functions in head injury management:

• Severity classification:

  • Severe TBI: GCS 3-8
  • Moderate TBI: GCS 9-12
  • Mild TBI: GCS 13-15 1

• Detection of deterioration: Serial GCS assessments are crucial for identifying neurological worsening that may require urgent intervention 1

• Prognostic indicator: GCS scores strongly correlate with outcomes in traumatic brain injury, posterior circulation stroke, and post-cardiac arrest 1

• Communication tool: Provides standardized terminology for describing neurological status across healthcare settings 1

• Triage decision-making: Helps determine appropriate level of care and need for neurosurgical intervention 1

Interpretation of GCS Scores

Key Interpretation Principles

1. Serial assessments are more valuable than single measurements

   • A low GCS score that remains low or a high score that decreases predicts poorer outcomes
   • A high GCS score that remains high or a low score that progressively improves suggests better outcomes 1

2. The motor component is most robust

   • When sedation or intubation limits assessment, the motor score remains the most reliable component 1
   • The motor response correlates well with injury severity even in sedated patients

3. GCS <14 warrants trauma center transport

   • Field triage guidelines recommend transport to a trauma center for patients with GCS <14 1

4. Integration with other findings

   • Pupillary responses should be assessed alongside GCS for more accurate prognostication 1
   • Combining GCS with pupillary assessment provides greater specificity in outcome prediction

Limitations and Pitfalls

1. Intubation and sedation

   • Verbal component cannot be assessed in intubated patients
   • Sedation and neuromuscular blockade confound accurate scoring 1

2. Single score limitations

   • A single GCS determination has limited prognostic value for mild TBI 1
   • Approximately 13% of patients who later became comatose initially had GCS of 15 1

3. Skewed weighting

   • The scale has numerical skew toward the motor response 2

4. Limited application outside TBI

   • Not recommended for patients without traumatic brain injury 3
   • Other assessment tools may be more appropriate for non-TBI patients

5. Lack of brainstem reflex assessment

   • Does not incorporate important brainstem reflexes that have prognostic value 2
   • Newer scales like the FOUR score include brainstem assessment 4

Best Practices for GCS Assessment

1. Perform serial assessments

   • For moderate TBI (GCS 9-13), assessments should be performed frequently (every 15-60 minutes initially) 1
   • Any decrease of at least two points warrants immediate reevaluation and possible repeat imaging 1

2. Document all three components separately

   • Record eye, verbal, and motor scores individually, not just the total 1
   • This provides more detailed information about the specific deficits

3. Consider confounding factors

   • Account for effects of sedation, intoxication, and metabolic disturbances
   • Note presence of orbital swelling, endotracheal intubation, or language barriers

4. Integrate with pupillary assessment

   • Evaluate pupil size and reactivity alongside GCS 1
   • Abnormal pupillary responses with decreased GCS suggest increased intracranial pressure

5. Use appropriate alternatives when needed

   • Consider the FOUR score for intubated patients or when more detailed brainstem assessment is needed 1, 4

Conclusion

The Glasgow Coma Scale remains the most widely used tool for assessing consciousness in head-injured patients despite its limitations. Its greatest value lies in serial assessments to detect neurological deterioration rather than as a single prognostic indicator. When properly applied with an understanding of its limitations, the GCS provides crucial information for clinical decision-making and communication in traumatic brain injury management.