How is muscle weakness assessed in the Intensive Care Unit (ICU)?

From the Guidelines

Muscle weakness in the ICU is best assessed through a combination of clinical examinations and standardized tools, with the Medical Research Council (MRC) Sum Score being the most widely used method, as recommended by recent guidelines 1.

Assessment Methods

The MRC Sum Score involves testing six muscle groups bilaterally on a 0-5 scale, with a maximum score of 60 and scores below 48 indicating significant weakness.

• Handgrip dynamometry provides objective strength measurements and can detect early weakness.
• For sedated or uncooperative patients, physical examination findings like flaccid limbs and diminished reflexes may be used.
• Ultrasound can assess muscle thickness and quality non-invasively.
• Electrophysiological studies such as electromyography (EMG) and nerve conduction studies help differentiate between neuropathic and myopathic causes of weakness, as outlined in a clinical practice guideline 1.

Importance of Regular Assessments

Regular assessments are crucial, typically performed daily when possible, to track changes in muscle function and guide rehabilitation strategies.

• The Confusion Assessment Method for ICU (CAM-ICU) is often performed alongside strength assessments to evaluate delirium, which can affect test reliability.
• ICU-acquired weakness affects up to 50% of critically ill patients and can significantly impact recovery outcomes, highlighting the need for early identification and intervention, as discussed in a study on ICUAW diagnosis 1.

From the Research

Assessment of Muscle Weakness in ICU

Muscle weakness in the Intensive Care Unit (ICU) is a common condition that can be caused by various factors, including critical illness polyneuropathy, myopathy, and muscle atrophy. The assessment of muscle weakness in ICU patients is crucial for diagnosis, treatment, and prognosis.

Diagnosis of Muscle Weakness

The diagnosis of muscle weakness in ICU patients can be clinical, based on:

• Medical Research Council sum score 2
• Handgrip dynamometry for limb weakness 2
• Recognition of a patient's ventilator dependency or difficult weaning from artificial ventilation for diaphragmatic weakness 2 Additional electrophysiological tests, such as the peroneal nerve test (PENT), can be used as a screening test in non-cooperative patients 2. Muscular ultrasonography can also be used to assess skeletal muscle mass and detect muscle weakness 3.

Tools for Assessment

Various tools can be used to assess muscle weakness in ICU patients, including:

• Manual muscle testing 4
• Electrophysiological investigations, such as electromyography (EMG) and nerve conduction studies (NCS) 5
• Muscle biopsy 4
• Muscular ultrasonography 3
• Medical Research Council sum score [(2,6)]

Factors Influencing Assessment

Several factors can influence the assessment of muscle weakness in ICU patients, including:

• Delirium [(2,4)]
• Nutritional status [(2,4)]
• Age and comorbidities [(3,6)]
• Severity of illness and organ failure 6
• Use of corticosteroids and neuromuscular blocking agents 6

Importance of Early Assessment

Early assessment of muscle weakness in ICU patients is crucial for:

• Identifying patients at risk of developing muscle weakness 6
• Initiating early mobilization and rehabilitation [(2,4)]
• Improving outcomes and reducing the risk of long-term physical, cognitive, and mental impairments 4