Predictors of acute muscle loss in the intensive care unit: A secondary analysis of an in-bed cycling trial for critically ill patients

Purpose: The purpose of this study was to assist clinicians to identify critically ill patients at greatest risk of acute muscle loss and to analyse the associations between protein intake and exercise on acute muscle loss. Materials and methods: Secondary analysis of a single-centre randomised clinical trial of in-bed cycling using a mixed effects model was undertaken to examine the association between key variables and rectus femoris cross-sectional area (RFCSA). Groups were combined, and key variables for the cohort were modified Nutrition Risk in the Critically Ill (mNUTRIC) scores within the first days following intensive care unit admission, longitudinal RFCSA measurements, percent of daily recommended protein intake, and group allocation (usual care, in-bed cycling). RFCSA ultrasound measurements were taken at baseline and days 3, 7, and 10 to quantify acute muscle loss. All patients received usual care nutritional intake while in the intensive care unit. Patients allocated to the cycling group commenced in-bed cycling once safety criteria were met. Results: Analysis included all 72 participants, of which 69% were male, with a mean (standard deviation) age of 56 (17) years. Patients received a mean (standard deviation) of 59% (26%) of the minimum protein dose recommended for critically ill patients. Mixed-effects model results indicated that patients with higher mNUTRIC scores experienced greater RFCSA loss (estimate = -0.41; 95% confidence interval [CI] = -0.59 to -0.23). RFCSA did not share a statistically significant association with cycling group allocation (estimate = -0.59, 95% CI = -1.53 to 0.34), the percentage of protein requirements received (estimate = -0.48; 95% CI = -1.16 to 0.19), or a combination of cycling group allocation and higher protein intake (estimate = 0.33, 95% CI = -0.76 to 1.43). Conclusions and relevance: We found that a higher mNUTRIC score was associated with greater muscle loss, but we did not observe a relationship between combined protein delivery and in-bed cycling and muscle loss. The low protein doses achieved may have impacted the potential for exercise or nutrition strategies to reduce acute muscle loss. Trial registration: Australian and New Zealand Clinical Trials Registry (ACTRN 12616000948493) Crown Copyright (c) 2023 Published by Elsevier Ltd on behalf of Australian College of Critical Care Nurses Ltd. All rights reserved.