Skeletal muscle mass and mortality - but what about functional outcome?

We have known for over a decade that critical illness survivors suffer from significant functional disability after hospital discharge. Muscle wasting is a major contributor to this disability, occurring early and rapidly during critical illness, with the subsequent weakness associated with delayed weaning and prolonged hospital stay. The scale of this long-term public health issue is concerning for two important reasons: increasing numbers of patients survive critical illness, and this is compounded by the lack of interventions to reduce skeletal muscle wasting to combat the functional disability. In the current issue of Critical Care, Weijs and colleagues demonstrate an indirect relationship between skeletal muscle mass on admission to the ICU and mortality. Observational data were obtained from 240 critically ill patients, all of whom received abdominal computer tomography scans for clinical reasons. Skeletal muscle volume was calculated for all visible skeletal muscle at the level of the third lumbar vertebra. In both continuous and categorical regression analysis, lower muscle volume on admission was associated with higher mortality, independent of Acute Physiology and Chronic Health Evaluation II score and gender. Interestingly, no association was observed between mortality and body mass index. These data also demonstrate that more than twice as many critical illness survivors with a low muscle mass on admission, compared to those with preserved muscle mass, were discharged to a nursing home. While this approach is novel and the results support the current clinical view in this area, one must regard these data with caution. Clinically relevant details, such as prior functional status, are not available. Despite these caveats, this study has two main messages. Firstly, muscle mass on admission to the ICU is a predictor of mortality and this physiological biomarker should therefore strongly be considered as an outcome measure in interventional studies. Secondly, low admission muscle mass is associated with increased disability and, in the case of this study, associated with an increased frequency of discharge to nursing homes. Further investigation is required to demonstrate the relationship between muscle mass, functional ability and discharge location.