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

Abstract
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.