How to improve the motor component of the Glasgow Coma Scale (GCS)?

How to Assess the Motor Component of the Glasgow Coma Scale

The motor component of the GCS should be assessed by applying a painful stimulus and observing the best motor response, scored from 1 to 6, with the patient's ability to obey commands (M6) representing the highest score and no motor response (M1) the lowest. 1

Standardized Motor Response Scoring

The motor component uses a 6-point scale with specific criteria for each level:

• M6 (Obeys commands): Patient follows simple motor commands such as "squeeze my hand" or "wiggle your toes" 1
• M5 (Localizes to pain): Patient moves purposefully toward the painful stimulus in an attempt to remove it 1
• M4 (Withdraws from pain): Patient pulls away from painful stimulus but does not localize to it 1
• M3 (Abnormal flexion/decorticate posturing): Patient exhibits flexion of arms with extension of legs in response to pain 1
• M2 (Abnormal extension/decerebrate posturing): Patient exhibits extension of both arms and legs in response to pain 1
• M1 (No motor response): Patient shows no movement in response to painful stimulation 1

Critical Assessment Principles

Always document the individual motor score separately (e.g., E3V4M5) rather than just the sum, as patients with identical total GCS scores but different component profiles have vastly different outcomes and prognoses. 1

• Apply a standardized painful stimulus to elicit the motor response—acceptable methods include supraorbital pressure, trapezius squeeze, or nail bed pressure 1
• Record the best motor response observed from either side of the body, as asymmetric responses may indicate focal neurologic injury 1
• Assess pupils simultaneously with the motor score, as pupillary size and reactivity are key prognostic indicators that complement motor findings 1

Timing and Frequency of Motor Assessments

The frequency of motor component assessment depends on injury severity:

• For severe TBI (GCS 3-8): Assess every 15 minutes initially, then hourly once stable 1
• For moderate TBI (GCS 9-12): Assess every 15 minutes for the first 2 hours, then hourly for 12 hours, continuing hourly until stable 1
• For mild TBI (GCS 13-15) with motor score concerns: More frequent monitoring is warranted if total GCS <14, as mortality reaches 24.7% at this threshold 1

Prognostic Value of Motor Scores

A GCS motor score >3 on day 4 after cardiac arrest predicts favorable outcome at 6 months with 84% specificity and 77% sensitivity. 2

• In post-cardiac arrest patients, assess the motor score within the first 4 days to identify those with scores >3, which indicates increased likelihood of favorable outcome 2
• A motor score of 4-5 evaluated on ICU admission after cardiac arrest predicts favorable outcome at 3 months with 98% specificity 2
• Serial motor assessments provide substantially more valuable clinical information than single determinations, with declining scores indicating poorer prognosis 1

Important Confounding Factors

Sedation and pain medication significantly influence motor score assessment, and adequate time must elapse after stopping these medications to achieve reliable results. 2

• In post-cardiac arrest patients not treated with therapeutic hypothermia, absent motor response (M1) at 72 hours predicts poor outcome, though with a 5% false-positive rate 2
• For patients treated with therapeutic hypothermia, a motor score ≤2 at day 3 after sustained ROSC is considered a potentially unreliable prognosticator of poor outcome 2
• Neuromuscular blockers, hypotension, and ongoing sedation all invalidate motor score assessment and must be discontinued with appropriate washout time before reliable testing 2

Special Considerations for Intubated Patients

• While intubation prevents verbal response assessment, the motor component remains fully assessable and is the most critical prognostic element of the GCS 3
• The motor score can be combined with eye opening scores using regression models to estimate expected verbal response in intubated patients, though this is primarily for research purposes 3
• In intubated patients, the motor component becomes the primary driver of clinical decision-making regarding neurologic status 3

Clinical Pitfalls to Avoid

• Never use motor score alone for withdrawal of life-sustaining therapy decisions—any withdrawal in post-cardiac arrest patients should use multiple prognostication modalities according to established protocols 2
• Do not assess motor response during or immediately after seizure activity, as post-ictal states temporarily depress motor function 2
• Avoid assessing motor response in the presence of spinal cord injury below the level being tested, as this will artificially lower the score 4
• A motor score of M1 (no response) requires verification that adequate painful stimulus was applied and that no confounding medications are present 2