Ultrasound-based upper limb muscle thickness is useful for screening low muscularity during intensive care unit admission: A retrospective study.

Background & Aims: Malnutrition is associated with poor outcomes. Muscle mass is an important malnutrition indicator included in Global Leadership Initiative on Malnutrition (GLIM) criteria. Although bioelectrical impedance analysis and dual-energy X-ray absorptiometry are common muscle mass assessment methods, they are unreliable during intensive care unit (ICU) admission due to the influence of dynamic fluid changes. We hypothesized that ultrasound-based upper limb muscle assessment would be useful for assessing muscularity at ICU admission.

Methods: We retrospectively analyzed prospectively obtained ultrasound data from patients admitted to an ICU. We excluded patients without computed tomography (CT) imaging of the third lumbar vertebra within 2 days of ICU admission. Primary outcomes were the diagnostic utility of ultrasound-based upper limb muscle thickness for assessing low muscularity by CT. Low muscularity was defined as a skeletal muscle index of 36.0 cm/m for males and 29.0 cm/m for females at the cross-sectional area of the third lumbar vertebrae. Secondary outcomes of this study included the relationships between upper limb muscle thickness and biceps brachii muscle cross-sectional area, quadriceps femoris thickness, rectus femoris cross-sectional area.

Results: Among 64 patients assessed by ultrasound, 52 had CT examination records and were included in the analysis. The mean age was 70 ± 13 years, and the mean body mass index was 23.3 ± 4.2 kg/m. Upper limb muscle thickness had the discriminative power to assess low muscularity at an area under the curve of 0.77 (95% CI [confidence interval], 0.63-0.91); the cutoff value (26.8 cm) had 84.6% sensitivity and 66.7% specificity. The upper limb muscle index had the discriminative power to assess low muscularity at an area under the curve of 0.80 (95% CI, 0.68-0.93); the cutoff value (9.9 mm/m) had 76.9% sensitivity and 71.8% specificity. Upper limb muscle thickness was correlated with upper limb muscle cross-sectional area, quadriceps femoris muscle thickness, rectus femoris muscle cross-sectional area (r = 0.39-0.76, p < 0.01, n = 52).

Conclusions: Ultrasound-based upper limb muscle thickness assessments can screen for low muscularity upon ICU admission.