Comparing bedside and CT-derived muscle mass assessment methodologies at intensive care unit admission: A critical step towards bedside detection of reduced muscle mass.

BACKGROUND AND AIMS: Reduced skeletal muscle mass at Intensive Care Unit (ICU) admission is associated with increased mortality. Bedside techniques, including bioelectrical impedance analysis (BIA), ultrasonography (US), and calf circumference (CC), may help to estimate skeletal muscle mass in critically ill patients. This study aimed to investigate the accuracy of these bedside methods in assessing muscle mass compared to lumbar 3 (L3) CT-derived skeletal muscle index (CT-SMI) and determine cut-offs for reduced muscle mass upon ICU admission.

METHODS

A prospective, single-centre, cohort study conducted between May 2023 and April 2025. Patients (≥18 years) with an expected ICU stay ≥3 days were included. Bedside parameters (<48 h of ICU admission) included multifrequency BIA-derived skeletal muscle mass (BIA-SMM) and fat-free mass (BIA-FFM)), US-derived rectus femoris cross-sectional area (US-RFCSA) and quadriceps muscle layer thickness (US-QMLT), and CC (adjusted for BMI). These were compared to L3 CT-SMI and CT-derived skeletal muscle area (CT-SMA) retrieved 7 days before to 24 h after ICU admission. Correlations between CT and bedside methods were assessed. Reduced muscle mass was defined using CT-based SMI cut-offs (females <38 cm2/m2; males <50 cm2/m2) to determine cut-off values of bedside parameters using ROC analyses.

RESULTS

Fifty-six ICU patients (70 % male) were included, showing 64 % having reduced skeletal muscle mass. Correlations of CT-SMI with BIA and US parameters were weak to moderate (r = 0.36-0.45, all p < 0.05), while CT-SMA correlated moderately with BIA-FFM (r = 0.57) and BIA-SMM (r = 0.62, both p < 0.001) but not with US-RFCSA, US-QMLT, and CC (p > 0.05). Cut-offs for reduced skeletal muscle mass were BIA-FFMI: 23.8 kg/m2 and 20.0 kg/m2; BIA-SMMI: 13.4 kg/m2 and 10.7 kg/m2; adjusted CC: 36.8 cm and 33.8 cm, in males and females, respectively, and US-RFCSA: 4.3 cm2 and US-QMLT: 2.3 cm (both sexes).

CONCLUSION

At ICU admission, correlations between bedside methods and L3 CT-derived muscle mass were low to moderate. Cut-off values were derived to detect reduced skeletal muscle upon ICU admission. However, further validation is required before clinical implementation.