Longitudinal changes of skeletal muscle mass and architecture in critically ill adults: A prospective matched cohort...

Skeletal muscle loss is a common consequence of critical illness, yet its determinants and prognostic significance remain unclear. This study investigated muscle trajectory during hospitalization in critically ill patients, factors predicting these changes, and the associations between early muscle changes with clinical and functional outcomes.

Adults (≥18 years) with severe pneumonia requiring supplemental oxygen were enrolled within 72 h of ICU admission. Two groups were recruited: RT-PCR-confirmed COVID-19 and non-COVID pneumonia, individually matched by age (±10 years), sex, and ventilatory support. Ultrasound assessments of quadriceps muscles (quadriceps muscle layer thickness, rectus femoris cross-sectional area, pennation angle, fascicle length) and forearm muscle thickness were performed in the ICU on study Days 1, 7, and 14, at ICU discharge (if later), and at hospital discharge. Muscle trajectories were evaluated using linear mixed-effects models. Regression analyses examined associations of relative muscle changes with (1) potential predictors, (2) 60-day time-to-discharge alive, and (3) hospital discharge handgrip and knee extension strength.

Fifty-nine patients (29 COVID-19, 30 non-COVID) were analyzed. Quadriceps muscles changed significantly over time, while forearm muscle thickness did not; trajectories were comparable between groups. No patient characteristics, laboratory, or clinical factors were associated with muscle changes on Day 7 or hospital discharge. Day 7 muscle changes were not associated with time-to-discharge-alive at 60 days or muscle strength after baseline adjustment (all p > 0.05).

In critically ill patients, significant muscle changes occurred during hospitalization irrespective of COVID-19 status, but no predictors were identified. Early muscle change alone was not predictive of clinical or functional outcomes.

This study demonstrates that skeletal muscle changes significantly over the course of hospitalization with similar trajectories in COVID-19 and non-COVID patients, independent of patient characteristics or routine clinical and laboratory factors. Early muscle loss alone was not predictive of clinical and functional outcomes, highlighting the need for combined or alternative markers to better identify high-risk patients and guide targeted interventions in critical care.