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.