Differences in muscle atrophy between the lower limbs and the accessory respiratory muscles in critically ill patients.

Purpose: This study aimed to investigate muscle atrophy in critically ill patients using ultrasonography. We compared the rectus femoris (a major muscle of the lower limbs) with the sternocleidomastoid (an accessory respiratory muscle).

Methods: Thirty-four patients hospitalized at the Critical Care Medical Center of Kindai University Hospital between January 2022 and March 2023 were enrolled. Muscle dysfunction was measured based on the thickness and cross-sectional area of the rectus femoris and sternocleidomastoid using ultrasonography. These values were evaluated every alternate day for 13 days after admission or until discharge, whichever occurred first. Factors that correlated with percentage changes in sternocleidomastoid thickness were also analyzed.

Results: The mean age of the patients was 67.3 ± 15.3 years, and 20 (59%) were men. Seven patients (21%) were admitted for trauma, and 27 (79%) for medical or other non-trauma-related emergency conditions. The rectus femoris thickness and cross-sectional area significantly decreased after day 7 (P < 0.05). There was no significant change in sternocleidomastoid thickness. However, it negatively correlated with the length of hospitalization and duration of mechanical ventilation use (r = - 0.38, P < 0.05; r = - 0.64, P < 0.05, respectively).

Conclusion: Although rectus femoris thickness decreased significantly, changes in sternocleidomastoid thickness may be related to the use of mechanical ventilation.