Abstract
IntroductionImpaired skeletal muscle function has important clinical outcome implications for survivors of critical illness. Previous studies employing volitional manual muscle testing for diagnosing intensive care unit-acquired weakness (ICU-AW) during the early stages of critical illness have only provided limited data on outcome. This study aimed to determine inter-observer agreement and clinical predictive value of the Medical Research Council sum score (MRC-SS) test in critically ill patients.MethodsStudy 1: Inter-observer agreement for ICU-AW between two clinicians in critically ill patients within ICU (n = 20) was compared with simulated presentations (n = 20). Study 2: MRC-SS at awakening in an unselected sequential ICU cohort was used to determine the clinical predictive value (n = 94) for outcomes of ICU and hospital mortality and length of stay.ResultsAlthough the intra-class correlation coefficient (ICC) for MRC-SS in the ICU was 0.94 (95% CI 0.85–0.98), κ statistic for diagnosis of ICU-AW (MRC-SS <48/60) was only 0.60 (95% CI 0.25–0.95). Agreement for simulated weakness presentations was almost complete (ICC 1.0 (95% CI 0.99–1.0), with a κ statistic of 1.0 (95% CI 1.0–1.0)). There was no association observed between ability to perform the MRC-SS and clinical outcome and no association between ICU-AW and mortality. Although ICU-AW demonstrated limited positive predictive value for ICU (54.2%; 95% CI 39.2–68.6) and hospital (66.7%; 95% CI 51.6–79.6) length of stay, the negative predictive value for ICU length of stay was clinically acceptable (88.2%; 95% CI 63.6–98.5).ConclusionsThese data highlight the limited clinical applicability of volitional muscle strength testing in critically ill patients. Alternative non-volitional strategies are required for assessment and monitoring of muscle function in the early stages of critical illness.
Highlights
Impaired skeletal muscle function has important clinical outcome implications for survivors of critical illness
In study 2, we investigated the clinical predictive value of ability to perform Medical Research Council sum score (MRC-SS) at awakening and the degree to which MRC-SS is indicative of intensive care unit-acquired weakness (ICU-AW)
The greatest sensitivity was observed at an MRC-SS less than 35 (64.3%) with 64.9% specificity (area under the curve (AUC): 0.69) for ICU length of stay (LOS), and the greatest specificity was observed at an MRC-SS less than 29.5 (70.2%) with 62.5% sensitivity (AUC: 0.63) for ICU mortality, albeit that these ‘cutoffs’ have limited clinical usefulness
Summary
This study aimed to determine inter-observer agreement and clinical predictive value of the Medical Research Council sum score (MRC-SS) test in critically ill patients. More thorough assessment of delirium and complex cognitive ability may have addressed this problem [25], but we aimed to reflect the common approach employed in previous studies [6,7,10,19]
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