How can manual muscle testing (MMT) be performed and graded in an unconscious patient?

Manual Muscle Testing in Unconscious Patients

In unconscious patients, traditional manual muscle testing (MMT) using the Medical Research Council (MRC) scale cannot be performed because it requires patient cooperation and the ability to follow commands; instead, muscle assessment must rely on ultrasound measurement of muscle thickness as a non-validated alternative, or defer testing until the patient regains consciousness. 1

Why Traditional MMT Cannot Be Performed

• MMT requires active patient participation including the ability to follow two-step commands, maintain specific positions, and generate voluntary muscle contractions against resistance 2
• The standard MRC scale grades muscle strength from 0-5 based on the patient's ability to move against gravity and resistance, which is impossible without consciousness 1
• Manual muscle testing during critical illness is not feasible for most patients due to coma, delirium, and/or altered mental status 3
• Among 135 critically ill patients screened in one study, most were precluded from MMT participation specifically because of altered mental status 3

Alternative Assessment Methods for Unconscious Patients

Ultrasound Muscle Thickness Measurement

• In unconscious individuals, measurement of muscle thickness by ultrasound is available as a non-validated test for assessing muscle mass 1
• Muscle ultrasound is noninvasive, can be applied even in non-collaborative patients, and appears economically viable without requiring specialized staff or X-ray exposure 1
• Ultrasound measures are scarcely influenced by rapid fluid shifts in critically ill patients 1
• While lacking cutoff values to identify low muscle mass, ultrasound may be valuable for monitoring muscle mass changes over time and assessing effectiveness of interventions 1

Motor Response Assessment Without Volitional Testing

• In unconscious patients, motor assessment is limited to observing reflexive responses to stimulation rather than graded voluntary strength 4, 5
• The Glasgow Coma Scale motor component (scored 1-6) can document motor responses ranging from no response to obeying commands, but this is not equivalent to MMT 4, 5
• The FOUR Score evaluates motor response as part of consciousness assessment but does not provide muscle-specific strength grading 4, 6

Clinical Algorithm for Muscle Assessment in Unconscious Patients

Step 1: Assess Level of Consciousness

• Use the Glasgow Coma Scale or FOUR Score to determine if the patient can follow commands 4, 6
• If GCS motor score is less than 6 (not obeying commands), traditional MMT cannot be performed 4

Step 2: Consider Alternative Monitoring

• Implement ultrasound muscle thickness measurements for serial monitoring if available, recognizing this is non-validated 1
• Document baseline measurements for comparison during recovery 1

Step 3: Implement Preventive Interventions

• Initiate passive range of motion exercises, continuous passive motion (CPM), and neuromuscular electrical stimulation (NMES) to prevent muscle atrophy without requiring patient cooperation 1
• These interventions do not interfere with sedation or renal replacement therapy 1

Step 4: Plan for Serial Assessment Upon Awakening

• Defer formal MMT until the patient regains the ability to follow two-step commands 3, 2
• Interobserver agreement for MMT improves substantially after ICU discharge compared to during critical illness (Cohen's kappa 1.0 vs 0.38), suggesting delayed assessment may be more reliable 3

Critical Pitfalls to Avoid

• Do not attempt to grade muscle strength using the MRC scale in patients who cannot follow commands - the results will be invalid and potentially misleading 3, 2
• Do not confuse motor responses on consciousness scales (GCS, FOUR Score) with actual muscle strength testing - these assess different constructs 4, 6
• Be aware that some patients may have cognitive motor dissociation (CMD), where they retain cognitive function but cannot produce behavioral responses; these patients may show only subtle purposeful movements that require careful observation 7
• Motor assessment of limbs is only possible after reduction or discontinuation of sedation and neuromuscular blockers 6
• Fixed dilated pupils and absent motor responses during critical illness do not necessarily predict poor outcomes and should not be used as sole indicators of muscle function 6

When MMT Becomes Feasible

• MMT can be performed once the patient can tolerate sitting upright in bed and follow two-step commands 2
• The standard protocol tests six muscle groups bilaterally: shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion 2
• A sum score less than 48 out of 60 points defines ICU-acquired weakness when MMT becomes possible 3