Reliability and validity of the 4-point MRC scale for the diagnosis of intensive care unit-acquired weakness: a prospective study
Abstract
Objective: To determine the reliability and validity of the new 4-point Medical Research Council scale (MRC-4), compared with the traditional 6-point scale (MRC-6) and the handgrip strength dynamometry (HGD), in adult subjects who required mechanical ventilation (MV) in the intensive care unit (ICU).
Materials and methods: A prospective study conducted in four ICUs between January and November 2024. Subjects ≥18 years old who required MV for ≥48 h were included. Muscle strength was assessed using the MRC-4 and MRC-6 scales and the HGD. Reliability was calculated using the intraclass correlation coefficient (ICC), criterion validity was assessed by the ROC curve, and construct validity was evaluated through correlation analyses.
Results: A total of 60 subjects were evaluated. The intra-rater ICC for the MRC-6 and MRC-4 scales was 0.95 (95% CI: 0.89–0.98) and 0.94 (95% CI: 0.89–0.97) . The interrater ICC was 0.89 (95% CI: 0.86–0.93) and 0.87 (95% CI: 0.82–0.91), respectively. The MRC-6 scale was considered the reference method, and a cutoff of 25 on the MRC-4 scale yielded a sensitivity of 94.1% (95%CI: 73%–99%) and a specificity of 86% (95% CI: 72.7%–93.4%), with an area under the curve of 0.94. The correlation of the MRC-4 scale with the MRC-6 scale was high (ρ=0.83), as was the correlation with the HGD (ρ=0.70). Significant differences in the HGD were observed between sexes based on the diagnosis of ICU-acquired weakness using the MRC-4 scale.
Conclusion: The MRC-4 scale proved to be a reliable and valid tool for diagnosing ICU-acquired weakness in adult subjects.
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