Dynamic changes in quadriceps and diaphragm thickness for early diagnosis of ICU-acquired weakness in elderly ICU patients: a prospective bedside ultrasound study

Objective To investigate the value of bedside ultrasound in dynamically monitoring quadriceps and diaphragm thickness for early diagnosis of ICU-acquired weakness (ICU-AW) in elderly critically ill patients. Methods This prospective observational study enrolled elderly patients (aged ≥60 years) with an expected ICU stay of ≥7 days. Bedside ultrasound was performed on days 1 (D1), 3, 5, and 7 after ICU admission to measure rectus femoris cross-sectional area (RF-CSA), rectus femoris muscle layer thickness (RF-MLT), vastus intermedius muscle layer thickness (VI-MLT), end-inspiratory diaphragm thickness (DTei), and end-expiratory diaphragm thickness (DTee). Muscle strength was assessed using the Medical Research Council (MRC) sum score. The rates of change of each parameter were compared between the ICU-AW group (MRC ≤ 48) and non-ICU-AW group. Receiver operating characteristic (ROC) curves were used to evaluate predictive performance. Results Of 74 enrolled patients, 52 (70.3%) developed ICU-AW. No significant differences in baseline ultrasound parameters were found between groups. The rate of change of RF-MLT on D5 and D7 and the rate of change of DTee on D7 were significantly different between groups ( P = 0.049, 0.021, and 0.009, respectively). The rate of change of DTee on D7 showed the strongest negative correlation with MRC score ( r = −0.413, P < 0.001). ROC analysis showed that the D7 relative change in DTee had the numerically highest AUC (0.693, 95% CI: 0.556–0.830), with an optimal cutoff value of a decrease ≥6.07% (sensitivity 73.1%, specificity 59.1%), while RF-MLT yielded an AUC of 0.672 with a cutoff value of a decrease ≥3.45% (sensitivity 50.0%, specificity 86.4%). However, the difference between the two AUCs was small (0.021) and not formally tested, and the low specificity (59.1%) limits its clinical utility. Conclusion Progressive quadriceps and diaphragm atrophy occurs early in elderly ICU patients. The D7 relative change in DTee showed the numerically highest AUC among the evaluated parameters, suggesting modest discriminatory ability for ICU-AW and warranting further validation. Dynamic muscle ultrasound monitoring is feasible and reproducible at the bedside.