Muscle and Subcutaneous Tissue Variation by Ultrasound and Impedance Linked to Fluid Balance in ICU Patients

This cross-sectional study aims to investigate the relationship between variations in muscle thickness and subcutaneous tissue, measured by ultrasound, and fluid compartments, evaluated using bioelectrical impedance analysis (BIA), in critically ill patients in the intensive care unit (ICU). Critically ill patients frequently experience muscle wasting and tissue edema due to a combination of inflammation, immobilization, and aggressive fluid resuscitation protocols designed to counteract hemodynamic instability. Ultrasound is widely used to monitor muscle thickness because it is fast, non-invasive, and repeatable. However, muscle thickness measurements during the first days of ICU admission may be influenced by fluid overload, which causes edema and might lead to an overestimation of actual muscle mass. Bioelectrical impedance analysis (BIA) is a complementary tool that assesses both intra- and extracellular fluid compartments. This study aims to correlate daily fluid balance with changes in muscle thickness and subcutaneous tissue measured by ultrasound, and to determine if BIA can accurately reflect fluid status and potentially identify edema in these patients. Furthermore, at ICU discharge, patients' muscle strength will be assessed using both the MRC-sum score (0-60) and handgrip strength (using a Jamar dynamometer), to investigate whether the presence of edema at discharge correlates with muscle strength deficits. Data collection will occur daily, tracking fluid balance, clinical parameters, and body weight, alongside ultrasound and BIA measurements in a standardized position. The study will help clarify the interactions between fluid management, muscle mass changes, and clinical outcomes in critically ill patients, providing valuable insight into early rehabilitation strategies.