Lean mass as a risk factor for intensive care unit admission: an observational study

PURPOSE: Intensive care unit (ICU) survivors have reduced physical function likely due to skeletal muscle wasting and weakness acquired during critical illness. However, the contribution of pre-morbid muscle mass has not been elucidated. We aimed to examine the association between pre-ICU muscle mass and ICU admission risk. Secondary outcomes include the relationship between muscle mass and ICU outcomes. METHODS: ICU admissions between June 1, 1998, and February 1, 2019, were identified among participants of Geelong Osteoporosis Study (GOS), a population-based cohort study. Cox proportional hazard regression models estimated hazard ratios (HR) for ICU admission across T-score strata and continuous values of DXA-derived lean mass measures of skeletal mass index (SMI, lean mass/body mass %) and appendicular lean mass corrected for height (ALM/h2, kg/m2). Multivariable regression was used to determine the relationship between lean mass and ICU outcomes. RESULTS: One hundred and eighty-six of 3126 participants enrolled in GOS were admitted to the ICU during the follow-up period. In adjusted models, lean mass was not predictive of ICU admission (SMI: HR 0.99 95%CI 0.97-1.01, p = 0.32; ALM/h2: HR 1.11 95%CI 0.94-1.31, p = 0.23), while greater appendicular lean mass was related to reduced 28-day mortality (ALM/h2 adjOR: 0.25, 95%CI 0.10-0.63, p = 0.003, SMI adjOR: 0.91, 95%CI 0.82-1.02, p = 0.09). CONCLUSION: Lean mass was not associated with ICU admission in this population-based cohort study; however, greater appendicular lean mass was associated with reduced mortality. This suggests pre-ICU muscle status may not predict development of critical illness but is associated with better survival after critical illness occurs.