How do you measure the Glasgow Coma Scale (GCS)?

How to Measure the Glasgow Coma Scale (GCS)

Overview

The Glasgow Coma Scale is measured by assessing three components—eye opening, verbal response, and motor response—with scores ranging from 3 (deep coma) to 15 (fully awake), where each component is evaluated separately and then summed to produce the total GCS score. 1

The Three Components

Eye Opening Response (1-4 points)

• 1 point: Does not open eyes 1
• 2 points: Opens eyes in response to painful stimuli 1
• 3 points: Opens eyes in response to voice 1
• 4 points: Opens eyes spontaneously 1

Verbal Response (1-5 points)

• 1 point: Makes no sounds 1
• 2 points: Incomprehensible sounds 1
• 3 points: Utters inappropriate words 1
• 4 points: Confused, disoriented 1
• 5 points: Oriented, converses normally 1

Motor Response (1-6 points)

• 1 point: Makes no movements 1
• 2 points: Extension to painful stimuli (decerebrate response) 1
• 3 points: Abnormal flexion to painful stimuli (decorticate response) 1
• 4 points: Flexion/withdrawal to painful stimuli 1
• 5 points: Localizes painful stimuli 1
• 6 points: Obeys commands 1

Critical Assessment Principles

Serial GCS assessments are more valuable than a single measurement, as neurological deterioration over time is the key indicator of worsening intracranial pathology requiring intervention. 1, 2 The original developers emphasized that the GCS was designed for serial evaluations by relatively inexperienced care providers to facilitate communication between rotating shifts, not as a single diagnostic snapshot. 1

The motor component is the most difficult to assess accurately and requires the most careful attention and training. 3 Studies show that the motor component has the lowest accuracy among emergency providers (59.8%), compared to verbal (69.2%) and eye-opening (61.2%) components. 4

Special Situations

Intubated Patients

For intubated patients who cannot provide verbal responses, document the eye and motor scores and note that the verbal component cannot be assessed (often recorded as "GCS E_M_VT" where T indicates intubated). 5, 6 A regression model can predict the expected verbal score: Derived Verbal Score = -0.3756 + (Motor Score × 0.5713) + (Eye Score × 0.4233), though this is primarily used for research purposes. 6

Pediatric Patients

In children under 5 years old, use the pediatric GCS (pGCS) which modifies the verbal component to account for developmental limitations, though the AVPU scale (Alert, Verbal, Pain, Unresponsive) is often preferred in very young children who cannot follow commands. 1 The pGCS reliability has been questioned in very young children who may not understand orders and commands. 1

Common Pitfalls to Avoid

Overall GCS scoring accuracy among emergency providers is only 33.1%, with the motor component being the least accurate, so proper training and standardized assessment techniques are essential. 4 A concerning 9.2% of providers assign GCS scores that don't exist in the scoring system. 4

The GCS was never designed to diagnose mild or moderate traumatic brain injury with a single measurement—it was created to assess comatose patients with serial evaluations. 1 Using a single GCS score of 13-15 to determine "mild" injury can be misleading, as approximately 13% of patients who become comatose initially present with a GCS of 15. 1

A GCS score of 14 should not be dismissed as "mild" injury—patients with GCS 14 have approximately 23% risk of positive CT findings requiring intervention and should be considered high-risk. 7 In the original validation studies, patients admitted with GCS 14 could deteriorate rapidly to GCS 4 within hours. 1

Best Practices for Clinical Use

Assess GCS at regular intervals (every 5 minutes in prehospital setting, hourly in hospital) to detect deterioration, as trending is more important than any single value. 2 The three component scores should be documented separately as well as the sum, since the same total score can represent different clinical scenarios. 1

Apply painful stimuli systematically when assessing motor response—use central stimulation (supraorbital pressure or trapezius squeeze) rather than peripheral stimulation to accurately differentiate between localizing and withdrawal responses. 3 Proper technique and clear communication using standardized terminology prevents misinterpretation between healthcare providers. 3

Consider using the FOUR score (Full Outline of UnResponsiveness) as a complementary tool, particularly in intubated patients, as it provides greater neurological detail including brainstem reflexes and breathing patterns that the GCS cannot assess. 8 The FOUR score has excellent inter-rater reliability (κw = 0.82) and can distinguish patients with the lowest GCS scores into more granular categories. 8