Ultrasound assessment of muscle mass has potential to identify patients with low muscularity at intensive care unit admission: A retrospective study

Muscle mass is an important biomarker of survival from a critical illness; however, there is no widely accepted method for routine assessment of low muscularity at intensive care unit (ICU) admission. We hypothesize that ultrasound-based partial muscle mass assessments can reflect the trunk muscle mass. Therefore, we aimed to investigate whether ultrasound muscle mass measurements could reflect trunk muscle mass and identify patients with low muscularity.We performed a retrospective analysis of prospectively obtained ultrasound data at ICU admission. We included patients who underwent computed tomography (CT) imaging at the third lumbar vertebra (L3) within 2 days before and 2 days after ICU admission. Primary outcomes included the correlation between the femoral muscle mass measurements using ultrasound and the cross-sectional area (CSA) at L3 obtained by CT. Low muscularity was defined as a skeletal muscle index of 36.0 cm2/m2 for males and 29.0 cm2/m2 for females. Secondary outcomes included the correlation with the ultrasound measurements of the biceps brachii muscle mass and diaphragm thickness.Among 133 patients, 89 underwent CT imaging, which included the L3. The patient mean age was 72 ± 13 years, and 60 patients (67%) were male. The correlation between the femoral muscle ultrasound and CT was ρ = 0.57 (p < 0.01, n = 89) and ρ = 0.48 (p < 0.01, n = 89) for quadriceps muscle layer thickness and rectus femoris muscle CSA, and these had the discriminative power to assess low muscularity, with the areas under the curve of 0.84 and 0.76, respectively. The ultrasound measurements of the biceps brachii muscle mass and diaphragm thickness were correlated with CT imaging [ρ = 0.57-0.60 (p < 0.01, n = 52) and ρ = 0.35 (p < 0.01, n = 79)].Ultrasound measurements of muscle mass were correlated with CT measurements, and the measurements of femoral muscle mass were useful to assess low muscularity at ICU admission.UMIN000044032 (retrospectively registered on April 25, 2021).