Association Between the Ultrasound Evaluation of Muscle Mass and Adverse Outcomes in Critically Ill Patients: A Prospective Cohort Study

BACKGROUND: Computed tomography (CT)-derived low muscle mass is associated with adverse outcomes in critically ill patients. Muscle ultrasound is a promising strategy for quantitating muscle mass. We evaluated the association between baseline ultrasound rectus femoris cross-sectional area (RF-CSA) and intensive care unit (ICU) mortality. Secondary outcomes were the determinants of RF-CSA, and the diagnostic performance of RF-CSA after adjustment for body size. METHODS: A prospective, single-center, observational cohort study was conducted in 3 ICUs (general, neuroscience, coronavirus disease-2019 [COVID-19]) of a university-affiliated hospital. Consecutive, mechanically ventilated patients with predicted length of stay >72 hours were included. RF-CSA was assessed at the dominant leg by ultrasound. Association with ICU mortality was tested using multivariable logistic regression. Diagnostic performance of RF-CSA was compared after adjustment by sex (CSA-sex), body surface area (CSA-BSA), and squared height (CSA-H2). RESULTS: A total of 316 patients were enrolled: age 69 [60-76], 211 men and 183 ICU survivors. Older age (odds ratio, OR [95% confidence interval, CI], 1.03 [1.01-1.05]), the type of ICU (neuroscience: 0.82 [0.38-1.79], COVID-19: 4.1 [2.01-8.38]), a higher modified Nutrition and Rehabilitation Investigators Consortium (NUTRIC) score (1.43 [1.21-1.70]), and a lower RF-CSA (0.41 [0.29-0.58]) were associated with ICU mortality. Baseline RF-CSA was lower in women, with higher nutritional risk, older age, and larger body size. Unadjusted RF-CSA had an area under the receiver operating characteristic (ROC) curve for ICU mortality of 0.720 [0.663-0.776], and this value was not significantly different from that of CSA-sex, CSA-BSA, and CSA-H2 (P = .1487). CONCLUSIONS: Low baseline RF-CSA was associated with increased ICU mortality. Admission RF-CSA was lower in women, with high nutritional risk, in older subjects and with lower body size. Absolute muscle mass was significantly associated with mortality, with no significant increase in this relationship when adjusting for sex or body size.