ICU-Acquired Weakness

Abstract

Survivorship after critical illness is an increasingly important health-care concern as ICU use continues to increase while ICU mortality is decreasing. Survivors of critical illness experience marked disability and impairments in physical and cognitive function that persist for years after their initial ICU stay. Newfound impairment is associated with increased health-care costs and use, reductions in health-related quality of life, and prolonged unemployment. Weakness, critical illness neuropathy and/or myopathy, and muscle atrophy are common in patients who are critically ill, with up to 80% of patients admitted to the ICU developing some form of neuromuscular dysfunction. ICU-acquired weakness (ICUAW) is associated with longer durations of mechanical ventilation and hospitalization, along with greater functional impairment for survivors. Although there is increasing recognition of ICUAW as a clinical entity, significant knowledge gaps exist concerning identifying patients at high risk for its development and understanding its role in long-term outcomes after critical illness. This review addresses the epidemiologic and pathophysiologic aspects of ICUAW; highlights the diagnostic challenges associated with its diagnosis in patients who are critically ill; and proposes, to our knowledge, a novel strategy for identifying ICUAW.

Keywords: ICU neuromuscular dysfunction; ICU rehabilitation; ICU-acquired weakness; critical illness myopathy; critical illness polyneuropathy.

Figure 1

Single fibular nerve conduction study. In a patient who is supine and normothermic, the recording active electrode (black) is placed over the extensor digitorum brevis muscle. The reference electrode (red) is placed over the fifth metatarsalphalangeal joint. Stimulation occurs 8 cm proximal to the active electrode, slightly lateral to the tibialis anterior tendon. Ground electrode (green) is placed between the stimulation site and the recording active electrode.

Figure 2

Proposed staged approach to diagnosis and treatment of ICU-acquired weakness. 6MWT = 6-min walk test; ADLs = activities of daily living; FSS-ICU = functional status score for the ICU; IMS = ICU Mobility Scale; MMT = manual muscle testing. *Note that many patients in the ICU will remain participatory and skip stage 1. Also note that specialized diagnostics are not recommended as standard clinical practice but rather for research or for evaluation of distinct clinical questions.