Serial ultrasound assessment of flexor carpi ulnaris and biceps brachii cross-sectional area in critically ill patients: A prospective cohort study
Keiichiro Aoki, Fumihito Kasai, Kazuki Komaba, Jin Saito, Akira Yoshikawa, Naonori Tashiro, Hiroyasu Inoue, Kengo Uchibori, Miwa FukazawaBackground
Serial ultrasound measurements may help characterize muscle wasting in critically ill patients. The flexor carpi ulnaris (FCU) is a superficial forearm muscle that may provide an additional assessment site. We described longitudinal FCU and biceps brachii (BB) cross-sectional area (CSA) changes and explored between-muscle differences and clinical associations.
Methods
This prospective two-center observational study enrolled 23 intensive care unit (ICU) patients; 20 were included in the analysis (median age, 57 years; range, 33–82). CSA was measured on days 0, 5, 7, and 14 after ICU admission. Analyses used Friedman tests, exact conditional Wilcoxon signed-rank tests with Bonferroni correction, and exploratory Spearman correlations. Post hoc between-muscle comparisons assessed participant-level percentage changes.
Results
Mean FCU CSA decreased from 1.36 to 1.08 cm² and mean BB CSA from 6.08 to 5.09 cm² over 14 days, corresponding to reductions of 20.9% and 16.4% in the unrounded group means. The median paired difference in percentage change (FCU minus BB) was −11.9 percentage points on day 7 (unadjusted p = 0.0023), meeting the Bonferroni threshold of 0.05/3. Differences on days 5 and 14 did not meet this threshold (p = 0.1429 and p = 0.2024). Baseline CSA values were correlated (ρ = 0.845, p < 0.001), as were 14-day percentage changes (ρ = 0.549, p = 0.0122); correlation p-values were unadjusted.
Conclusions
Serial ultrasound documented decreases in FCU and BB CSA in this small cohort, with an exploratory direct comparison identifying a greater proportional FCU decrease on day 7. These findings support further evaluation of FCU ultrasound as an additional muscle-monitoring measure. Its value for earlier detection of muscle wasting or diagnosis of ICU-acquired weakness requires direct validation.