Construct Validity of the Chilean-Spanish Version of the Functional Status Score for the Intensive Care Unit: A Prospective Observational Study Using Actigraphy in Mechanically Ventilated Patients

Objective: To evaluate the construct validity (hypotheses testing) of the Chilean-Spanish version of the Functional Status Score for the Intensive Care Unit (FSS-ICU) using continuous actigraphy from intensive care unit (ICU) admission to ICU discharge.

Design: The Chilean-Spanish version of the FSS-ICU was used in a prospective observational study to mainly evaluate its correlation with actigraphy variables. The FSS-ICU was assessed on awakening and at ICU discharge, while actigraphy variables were recorded from ICU admission to ICU discharge.

Setting: A 12-bed academic medical-surgical ICU.

Participants: Mechanically ventilated patients (N=30), of 92 patients screened.

Interventions: Not applicable.

Main outcome measures: Construct validity of the FSS-ICU Chilean-Spanish version was assessed by testing 12 hypotheses, including the correlation with activity counts, activity time (>99 counts/min), inactivity time (0-99 counts/min), muscle strength, ICU length of stay, and duration of mechanical ventilation.

Results: The median FSS-ICU was 19 points (interquartile range [IQR], 10-26 points) on awakening and 28.5 points (IQR, 22-32 points) at ICU discharge. There was no floor/ceiling effect of the FSS-ICU at awakening (0%/0%) and only a ceiling effect at ICU discharge that was acceptable (0%/10%). Less activity time was associated with better mobility on the FSS-ICU at both awakening (ρ=-0.62, P<.001) and ICU discharge (ρ=-0.79, P<.001). Activity counts and activity time were not correlated as expected with the FSS-ICU.

Conclusions: The Chilean-Spanish FSS-ICU had a strong correlation with inactivity time during the ICU stay. These findings enhance the available clinimetric properties of the FSS-ICU.