Monitoring of Muscle Mass in Critically Ill Patients

The acute wasting of skeletal muscle is a recognized challenge in critical illness, and its extent correlates with prolonged ICU stays, heightened ICU and hospital mortality, and an increased likelihood of ICU-acquired weakness in survivors. The assessment of muscle mass serves two primary purposes: (1) evaluating patient lean body mass for diagnosing malnutrition and subsequent risk stratification, and (2) monitoring the progression of muscle loss or recovery during acute illness to tailor supportive or rehabilitation interventions. In the critical care environment, traditional tools for assessing muscle size and function are impractical due to patient cooperation challenges and significant fluid shifts. Therefore, there is a clear demand for standardized, easily administered, and non-volitional measurement tools. In recent years, several accurate methods for quantifying muscle mass and tracking changes over time have been validated. These include bioelectrical impedance analysis, computed tomography scans, and ultrasound imaging. While these tools show promise and are increasingly employed in the ICU, understanding their advantages and limitations is crucial. This chapter aims to describe these emerging imaging techniques, along with their limitations, providing key diagnostic insights for metabolic and nutritional support in the critical care setting.