A guided approach to diagnose severe muscle weakness in the intensive care unit

Intensive care unit (ICU) acquired muscle weakness (ICUAW) is a clinically detected condition characterized by diffuse, symmetric weakness involving the limbs and respiratory muscles.(1) Patients have different degrees of limb muscle weakness and are dependent on a ventilator, while the facial muscles are spared. Diagnosis of ICUAW requires that no plausible etiology other than critical illness be identified, and thus, other causes of acute muscle weakness are excluded. One major diagnostic criterion is that ICUAW is detected after the onset of critical illness; therefore, it is important to differentiate ICUAW from Guillain-Barrè syndrome or other acute neuromuscular disorders that may cause respiratory failure and ICU admission (Figure 1).(1) The use of neuromuscular blocking agents for long periods of time, the use of some antibiotics and electrolyte abnormalities, such as hypermagnesemia, hypokalemia, hypercalcemia, and hypophosphatemia, and prolonged immobilization are common in the ICU and should be appropriately treated before a diagnosis of ICUAW is posed.(2) A diagnosis of ICUAW is achieved by manually testing the muscle strength using the Medical Research Council (MRC) scale or by measuring handgrip strength using a dynamometer. MRC muscle strength is assessed in 12 muscle groups (Figure 2): a summed score below 48/60 designates ICUAW or significant weakness, and an MRC score below 36/48 indicates severe weakness.(3) Recently, a simplified version of the scale with only four categories and improved clinimetric properties was proposed (Figure 2).(4) To date, this version has been validated in a small cohort of 60 critically ill patients with excellent inter-rater reliability and high sensitivity and specificity in diagnosing ICUAW compared to complete full MRC.(5) Handgrip dynamometry measures isometric muscle strength and can be used as a quick diagnostic test. Cut-off scores of less than 11kg (IQR 10 40) in males and less than 7kg (IQR 0 7.3) in females are considered to be indicative of ICUAW (Figure 1).(5) Both MRC and handgrip dynamometry are volitional tests and require the patients to be alert, cooperative, and motivated. Sedation, delirium and coma often interfere with the early evaluation of muscle strength in the ICU. However, voluntary muscle strength using the MRC sum score or handgrip dynamometry can be reliably assessed if adequate clinical experience is gained with manual muscle testing in ICU patients and strict guidelines and the use of standardized test procedures and positions are followed to accurately select patients.(6) Common causes of ICUAW include critical illness polyneuropathy (CIP) and myopathy (CIM), which are revealed by appropriate nerve Nicola Latronico1,2, Rik Gosselink3