Physical Therapist Inter-Rater Reliability in Neuro-Muscle Ultrasound in Critically Ill Patients

Overview

The goal of this observational study is to evaluate the feasibility and inter-rater reliability of muscle and peripheral nerve ultrasound for the early detection of ICU-acquired weakness (ICU-AW) in critically ill patients. The main questions it aims to answer are: Can ICU physical therapists consistently measure muscle and nerve ultrasound variables such as muscle thickness, cross-sectional area, pennation angle, and echogenicity in critically ill patients? Do clinical scales (MRC-SS and FSS-ICU) show inter-evaluator agreement and correlate with ultrasound findings? Participants are adult ICU patients at Clínica INDISA who are undergoing routine neuromuscular assessments by trained physical therapists. Each patient will be evaluated by three independent raters using ultrasound and standardized clinical scales. Data will be collected and analyzed to determine inter-rater reliability and correlations between clinical and imaging findings.

This observational, cross-sectional pilot study aims to assess the inter-rater reliability of muscle and peripheral nerve ultrasound and functional clinical scales in the diagnosis of ICU-acquired weakness (ICU-AW). The study involves adult patients admitted to the Adult Critical Care Unit at Clínica INDISA (Santiago, Chile). Participants will undergo muscle ultrasound of the quadriceps (measuring anterior compartment thickness, cross-sectional area, and pennation angle) and peripheral nerve ultrasound (assessing cross-sectional area and echogenicity of specific nerves) performed by three trained physical therapists. Clinical assessments using the MRC Sum Score (MRC-SS) and the Functional Status Score for the ICU (FSS-ICU) will also be performed by each rater. The main aim is to evaluate the agreement between raters using the intraclass correlation coefficient (ICC) for ultrasound variables and Kendall's W for functional scales. The study will also explore correlations between clinical scores and ultrasound findings using Pearson or Spearman correlation coefficients. Echogenicity will be quantified using ImageJ software. All procedures are performed at bedside using portable ultrasound equipment, and evaluations follow safety guidelines for critically ill patients. The results of this study will contribute to validating physical therapists as reliable operators for early identification of ICU-AW using ultrasound-based tools and standardized clinical assessments.