Ultrasound- and circumference-based quadriceps mass is an independent predictor of 28-day mortality in critically ill patients

Background: Skeletal muscle mass is a key indicator of physiological reserve in critical illness. Objective: This study aimed to evaluate whether quadriceps mass assessed by bedside methods predicts 28-day mortality in critically ill patients. Methods: In this prospective study of 603 critically ill adults, we measured quadriceps thickness by ultrasonography under minimal transducer pressure (QT-min) and maximal transducer pressure (QT-max), quadriceps circumference (QC), and mid-upper arm circumference (MUAC) at admission. Cox regression was used to analyze the association between quadriceps thickness and 28-day mortality. Interaction and subgroup analyses were conducted for age, sex, BMI, mechanical ventilation, number of organ supports and vasopressor use. Results: < 0.05), with protective effects observed only in patients without these conditions. Conclusion: Bedside quadriceps mass assessment independently predicts 28-day mortality in critically ill patients, supporting its use for early risk stratification. In patients requiring vasopressors or organ support, the prognostic value of QT-min was attenuated, suggesting it may be susceptible to illness severity. However, given the small size of these subgroups, this finding warrants a cautious interpretation.