CPAx: Responsiveness and Minimal Clinically Important Difference

Intensive care unit (ICU) acquired weakness is a common complication associated with long-term physical impairments in survivors of a critical illness. The Chelsea Critical Care Physical Assessment tool (CPAx) is a valid and reliable instrument for physical function and activity in critically ill patients at risk for muscle weakness. However, its ability to measure change over time (responsiveness) and the minimal clinically important difference (MCID) have not yet been rigorously investigated. This multi-centre, mixed-methods, longitudinal cohort study therefore aims to establish responsiveness and the MCID of the CPAx in the target population from ICU baseline to ICU and hospital discharge. The study uses routine data from standard physiotherapy sessions like mobility, function and activity with no additional burden for critically ill adults. The investigators expect the CPAx to be responsive allowing its use as a primary outcome in future effectiveness trials for the treatment of ICU-acquired weakness using the newly established MCID for sample size calculation. A high quality, rigorously tested measurement tool for physical function and activity in the ICU should benefit researchers, clinicians and patients.