Muscle ultrasound: a reliable bedside tool for dietitians to monitor muscle mass

Abstract

Objectives: Monitoring muscle mass (cross-sectional area [CSA]) and quality (echogenicity) using ultrasound may help optimise nutrition support in the critically ill. However, to date, ultrasound imaging has not been included in the undergraduate training of dietitians, who are mostly responsible for the nutrition care of critically ill patients. This study assessed the accuracy and reliability of bedside imaging performed by a dietitian trained according to standardised methodology, followed by blinded analyses.
Methods: Two operators (a trainer and dietitian trainee) performed B-mode ultrasonography of the rectus femoris quadriceps muscle. For inter-rater accuracy, imaging was performed independently on 32 subjects by both operators, and for intra-rater reliability both obtained a second image on 15 subjects. A blinded assessor performed analyses (CSA and echogenicity) on all images. In a subset of 11 subjects, a musculoskeletal sonographer repeated all measurements. Inter- and intra-rater reliability were determined by calculating intraclass correlation coefficients (ICC), based on an absolute-agreement, 2-way mixed-effects model. An ICC > 0.75 was classified as good and > 0.90 as excellent.
Results: Intra- (ICC = 0.9–0.94) and inter-rater (ICC = 0.85–0.95) reliability of the imaging performed was good to excellent. No statistically significant differences were found between the two operators (mean difference for CSA = 0.18 cm², 95% CI = −0.38–0.03, p = 0.08; mean difference for echogenicity = 6.88, CI = −0.71–14.78, p = 0.07). Inter-rater reliability for image analyses was excellent (ICC = 0.97–1.0).
Conclusion: Bedside ultrasound performed by a dietitian trained according to standardised methodology shows good to excellent reliability and reproducibility. Training dietitians to perform bedside ultrasound may help to monitor muscle mass and quality in the critically ill.
Keywords: critical illness, ICU, muscle mass, muscle quality, bedside ultrasound, nutrition, ICU recovery