Association of peripheral muscle mass and in-hospital mortality in mechanically ventilated critically ill children: a prospective observational study.

Early muscle wasting in critically ill children during pediatric intensive care unit (PICU) admission correlates with poor clinical outcomes. This study aims to evaluate the predictive capability of ultrasound-measured loss rates in the biceps brachii (BB) and rectus femoris (RF) muscles for in-hospital mortality in pediatric patients. This is a single-center, prospective, observational study conducted from July 12, 2025, to October 22, 2025. It included children aged 1 month to < 18 years admitted to the PICU who required mechanical ventilation for at least 48 h. Ultrasound measurements were performed within 24 h of PICU admission (baseline) and on days 3, 5, and 7. Measurements included thickness and cross-sectional area (CSA) of the BB and RF. A total of 86 children were included. Analysis was performed on 86, 81, and 67 children at days 3, 5, and 7 of PICU admission, respectively. Continuous loss of BB and RF muscle mass occurred during the first week of PICU admission in critically ill children. Among children who died during hospitalization, RF CSA on days 3, 5, and 7, and BB CSA on day 3, showed greater decreases from baseline compared to the survivor group (p < 0.05). RF CSA loss ≥ 17.62% on day 5 demonstrated the highest predictive capability for in-hospital mortality, with an area under the receiver operating characteristic (AUROC) curve of 0.761 (0.645, 0.877), sensitivity of 72.2%, and specificity of 71.4%. The RF CSA < 17.62% on day 5 was associated with lower in-hospital mortality, with an adjusted hazard ratio (HR) of 0.076 (95% CI 0.014, 0.395, p = 0.002).

conclusionsDuring the first week of admission to the PICU, children experience continuous muscle wasting. Greater muscle loss correlates with poorer outcomes, and the rate of RF CSA loss on day 5 demonstrates good predictive capability for in-hospital mortality. Ultrasound-based muscle assessment helps identify children at higher risk of adverse in-hospital outcomes. WHAT'S KNOWN: • Early muscle wasting is a key prognostic risk factor in critically ill children. • Bedside ultrasound serves as a reliable tool for dynamic monitoring of muscle wasting. WHAT IS NEW: • This study quantifies the trajectory and magnitude of peripheral muscle wasting using serial ultrasound in mechanically ventilated children during the first PICU week, identifying a loss of ≥ 17.62% in rectus femoris cross-sectional area by day 5 as the strongest predictor of in-hospital mortality. • Early ultrasound monitoring provides an objective, bedside measure that may offer prognostic information alongside traditional severity scores.