Link between muscle function and physical function in critically ill patients

Abstract

Introduction: Improvements in intensive care unit (ICU) care has led to a growing number of survivors of critical illness, but not necessarily improved quality of life. After surviving critical illness, many critically ill survivors suffer from long-term complications such as reduced physical function, mental and cognitive dysfunction and a reduced health-related quality of life (HRQoL). Critically ill survivors develop a loss of muscle mass and muscle weakness of the respiratory and peripheral muscles. Therefore, the premise of this thesis was to determine whether muscle structure and function is associated with physical function in critically ill survivors. Methods: A scoping review was done to map the current understanding of muscle structure and function in critically ill patients. Six databases were searched using a data-base specific search strategy and papers were identified based on a familiarity with the literature. The primary investigator (PI) used a systematic process to extract data into a self-developed excel spreadsheet. The data obtained were used to inform the planning of the primary research study. A prospective observational cohort study was conducted to describe the outcomes of critically ill patients as well as determine the correlation between muscle structure, muscle function and physical function in critically ill patients at ICU discharge and hospital discharge. Mechanically ventilated participants were recruited within 24 hours of admission to the ICU. Measurements taken of muscle structure and function included ultrasonography of the diaphragm and peripheral muscles, the Medical Research Council-Sum Score (MRC-SS), dynamometry, maximal inspiratory pressure (MIP) and respiratory muscle endurance. The physical function and HRQoL measurements included the Chelsea Critical Care Physical Assessment (CPAx) tool, the de Morton Mobility Index (DEMMI), the Six-Minute Walk Test (6-MWT) and the EQ-5D-5L questionnaire. Associations between measures of muscle structure, muscle function and physical function were reported using Spearman's correlations. Stellenbosch University https://scholar.sun.ac.za IV Results: One thousand two hundred and eighty-two studies were retrieved and assessed for inclusion into the scoping review. After assessing for eligibility, thirty-four studies were included in the review. Data regarding muscle structure and function were predominantly from the developed countries. Assessments were focused on either muscle structure or muscle function, and not both. The methodology for the assessments of muscle structure and function were not standardised. Majority of assessments took place during ICU stay. The postural muscles were the least investigated. Forty-five participants were recruited for the primary research study. The median age of the sample was 34.5 (24.3 -47.4) years. Participants presented with changes in respiratory and peripheral muscle structure and function, and in physical function. A strong positive correlation was established between MIP and the 6-MWT (rho = 0....