Interrater Reliability of the Functional Status Score for the Intensive Care Unit

Abstract

Background: A decline in physical functioning is common during an intensive care unit (ICU) stay. The Functional Status Score for the Intensive Care Unit (FSS-ICU) is a performance-based measure designed to evaluate aspects of physical functioning in the ICU setting. While existing data support validity of the FSS-ICU, further investigation is needed regarding its interrater reliability. Objective: Evaluate interrater reliability of the FSS-ICU when completed by physical therapists (PTs), as part of routine clinical practice, across a wide range of patients with critical illness. Design: Prospective observational evaluation. Methods: Across patients in surgical, medical, and neurological ICUs, 8 PTs with 6 months of experience or more using the FSS-ICU (median [range] years of ICU experience = 2 [1-3]) administered the FSS-ICU. One of 2 reference rater PTs observed the FSS-ICU evaluation, and simultaneously scored it, with a minimum of 10 assessments per clinical PT. Reference rater and clinical PTs were blinded to each other's scores. Bland-Altman plots were constructed and intraclass correlation coefficients were computed using a random intercept (PT session and rater) model. Results: Eighty-one assessments on 76 different patients were observed by a reference rater PT. Bland-Altman plots revealed a mean difference in FSS-ICU scoring of 0.0 (95% limits of agreement: −4.0 to +4.0), with an intraclass correlation coefficient (95% confidence interval) of 0.985 (0.981-0.987). The intraclass correlation coefficients for patients in surgical, medical, and neurological ICUs were very similar: 0.984 (0.973-0.988), 0.987 (0.979-0.990), and 0.977 (0.963-0.983), respectively. Limitations: Single-center evaluation. Conclusions: The FSS-ICU evaluations, performed by PTs as part of routine clinical care across a variety of patients with critical illness, have excellent reliability compared with reference rater PTs.