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Introduction

Improvements in diagnosis and resuscitation of critically ill patients have prompted investigation into the burden of “survivorship.”15 Observational research has described substantial morbidity in survivors of critical illness, including general deconditioning, muscle weakness, dyspnea, depression, anxiety, and reduced health-related quality of life.6 A major catalyst for widespread attention was the comprehensive observations on a cohort of survivors of acute respiratory distress syndrome (ARDS).7 In this case series, patients were young and generally healthy prior to ARDS, and they experienced severe illness with prolonged critical care. Despite severe acute lung injury, serial follow-up examinations demonstrated that lung function generally normalized during the first year after ICU discharge. In contrast, all patients reported poor function attributed to the loss of muscle bulk, proximal limb weakness, and fatigue. Patients exhibited impaired endurance, and only 49% of patients had returned to work. At 5 years after ICU discharge, subjective weakness and decreased exercise capacity continued.8 Although 77% of patients were working by the fifth year, patients often required a modified work schedule, gradual transition back to work, or job retraining. In addition, patients were plagued with psychological illness. More than half of survivors experienced at least one episode of depression or anxiety.

Other investigations have reported similar findings of post-ARDS debilitation.9,10 An observational trial measured a 66% cumulative incidence of physical impairment during 2-year follow-up.9 The impairment, defined as the acquisition of two or more dependencies in instrumental activities of daily living, had greatest incidence by 3 months after discharge and was associated with longer ICU stay and prior depressive symptoms.

Acquired neuromuscular weaknesses, loss of function, and cognitive impairment have been measured in other critical care settings, such as in severe sepsis and during mechanical ventilation in the elderly. For example, the morbidity of a hospitalization for severe sepsis was evaluated utilizing a registry of Americans over age 50 years who underwent biennial evaluations of cognitive and physical function.11 Among patients with no functional limitations at baseline, hospitalization for severe sepsis was associated with the development of 1.57 new limitations, as well as a more rapid rate of development of functional limitations after hospitalization. In addition, the incidence of severe sepsis was highly associated with progression to moderate-to-severe cognitive impairment. Similar acquired disability has been observed in a longitudinal study of elderly patients undergoing hospitalizations that included need for mechanical ventilation.12 In adjusted analyses, mechanical ventilation was associated with a 30% greater disability in activities of daily living and a 14% greater disability in mobility.

These studies show that decrements in physical function occur across the spectrum of critical illness. Although outcomes may be influenced by other factors, such as age, pre-existing comorbidities, acquired psychological and cognitive dysfunction, and social support, it is clear that weakness needs to be recognized early to enable preventive interventions.

ICU-Acquired Weakness

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