Point-of-Care Ultrasound as a Prognostic Tool in Critically Ill Patients: Insights Beyond Core Muscle Mass

Background Muscle wasting is a critical and underrecognized determinant of outcomes in intensive care, yet conventional core muscle measurements such as computed tomography (CT)-derived L3 Skeletal Muscle Index (L3 SMI) may overlook localized muscle loss and be confounded by fluid shifts. Point-of-care ultrasound (POCUS) offers a bedside, repeatable method for assessing peripheral muscle thickness. Objectives To determine the prognostic value of peripheral muscle thickness, measured by POCUS, in predicting mortality, frailty, and functional outcomes in critically ill patients; and to compare these findings with core muscle mass assessed by L3 SMI. Design Prospective, single-center, observational study of critically ill adults admitted to the ICU with sepsis or requiring organ support. Methods Fifty critically ill adults meeting Sepsis-3 criteria or requiring respiratory/vasopressor support underwent POCUS assessments of biceps brachii, rectus femoris, and vastus intermedius thickness at days 1, 7, and 14 post-ICU admission. Twenty-eight patients also had CT scans within 7 days for L3 SMI calculation. The primary outcome was in-hospital mortality; secondary outcomes included Clinical Frailty Score and Zubrod/ECOG performance status, 90-day mortality and hospital readmission, and number of organ dysfunction-free days. Muscle measurements were analyzed both raw and indexed to body surface area, with predictive performance assessed via correlation and receiver operating characteristic analysis. Results Day 1 biceps brachii thickness strongly predicted in-hospital mortality (area under the curve [AUC] 0.84; sensitivity 1.0, specificity 0.67) and retained predictive value for 30-day and 90-day mortality. Vastus intermedius thickness on Day 1 was moderately predictive (AUC 0.79). At later time points, larger vastus intermedius measurements correlated negatively with ICU- and ventilator-free days, suggesting edema-related pseudohypertrophy. L3 SMI did not significantly correlate with ultrasound-based muscle measurements or clinical outcomes. POCUS-derived peripheral muscle indexing was associated with frailty indices, highlighting its role in capturing meaningful functional deficits. Conclusion POCUS-based muscle assessments, particularly of the biceps brachii and vastus intermedius, provide valuable prognostic insights beyond conventional L3 SMI.