Changes in cross sectional area of rectus femoris measured by ultrasonography were associated with ICU-AW in patients with critically ill

Purpose: This study aimed to compare two measurements of muscle atrophy in relation to muscle weakness in CIPs. We investigated the association between the sum of the medical research council scale scores (MRC-SS) and changes in muscle thickness and CSA of the rectus femoris, as measured by ultrasonography, in CIPs.

Methods: This was a single-center prospective cohort study of critically ill patients admitted to the critical care medical center at our hospital (Kindai University Hospital) between January 2022 and March 2023. We enrolled any critically ill patients admitted to the critical care medical center, in which our patients included: acute abdomen, sepsis, trauma, poison, acute lung disease, soft tissue infection, burn, cardiac arrest, and metabolic crisis. We measured the muscle thickness and the CSA of the RF by using ultrasonography. Measurements were made every other day post-admission. The two variables were evaluated and expressed as the percent change from day-1 measurement. Muscle weakness was assessed using MRC-SS, measured on the first day when the patients could sit in the edge-sitting position and follow five verbal commands. Patients with 48 points were diagnosed with ICU-AW.

Results: A total of 32 patients (mean age, 65.9 years) were recruited for this study. Seven patients (21%) were admitted for trauma, while 27 (79%) were admitted for medical and other emergencies. MRC score was 54.7±5.5 points. 5 patients (16%) were diagnosed as ICU-AW. It was measured at 7.9 ± 11.2 days after admission. RF muscle thickness and CSA were reduced by -6.3 ± 14.6% and -8.4 ± 13.4%, respectively, when the day the MRC-SS was measured. The MRC-SS was significantly correlated with changes in CSA at the day when the MRC-SS was measured (r=0.58, p0.01). However, no correlation was found between muscle thickness and the MRC-SS (r=0.01, p=0.97).

Conclusion: These findings suggest that CSA of the RF is more reliable variables for reflecting acute muscle weakness compared with muscle thickness. Decrease in CSA of the RF is important to predict ICU-AW in CIPs.

Implications: Measuring the MRC-SS may be challenging for patients with disorders of consciousness or those who are sedated and mechanically ventilated. In contrast, ultrasonography can be performed even under these conditions. Therefore, we should actively use ultrasonography in the ICU setting to predict ICU-AW.