Abstract
BACKGROUND: Factors associated with disability after critical illness are incompletely understood. Lower pre-existing muscle mass and muscle density on CT imaging are associated with greater mortality resulting from critical illness. Their relationship with disability and physical function in survivors of critical illness is unclear. RESEARCH QUESTION: We sought to understand the relationship between muscle mass and muscle density before critical illness and disability and self-reported physical function after surviving a critical illness. STUDY DESIGN AND METHODS: We conducted a nested cohort study of 125 survivors of critical illness with abdominal imaging between 6 months before and 4 days after ICU admission. We measured skeletal muscle cross-sectional area at the L3 vertebra, indexed by height, to obtain the skeletal muscle mass index and measured skeletal muscle density by calculating the mean Hounsfield units of the muscles. We recorded discharge location and, at 3 and 12 months after hospital discharge, assessed for disability with basic activities of daily living, instrumental activities of daily living, and self-reported physical function. We used multivariable regression to assess the relationship between baseline skeletal muscle mass index or density and outcomes. RESULTS: We found no association between skeletal muscle mass index and discharge to a facility or disability. However, lower skeletal muscle density was associated with greater odds of discharge to a facility, but not with disability at either time point. INTERPRETATION: A substantial percentage of participants (40%) demonstrated low muscle mass on abdominal imaging before seeking treatment for a critical illness. We did not find muscle mass or density to be associated with long-term disability or physical function after critical illness, although lower density was associated with increased risk of discharge to a facility. Further work is needed to understand the relationship between muscle health and physical recovery after critical illness. TRIAL REGISTRY: ClinicalTrials.gov; No.: NCT00392795; URL: www.clinicaltrials.gov.