An Exploratory Study of Long-Term Outcome Measures in Critical Illness Survivors: Construct Validity of Physical Activity, Frailty, and Health-Related Quality of Life Measures*

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Functional capacity is commonly impaired after critical illness. We sought to clarify the relationship between objective measures of physical activity, self-reported measures of health-related quality of life, and clinician reported global functioning capacity (frailty) in such patients, as well as the impact of prior chronic disease status on these functional outcomes.


Prospective outcome study of critical illness survivors.


Community-based follow-up.


Participants of the Musculoskeletal Ultrasound Study in Critical Care: Longitudinal Evaluation Study (NCT01106300), invasively ventilated for more than 48 hours and on the ICU greater than 7 days.



Measurements and Main Results:

Physical activity levels (health-related quality of life [36-item short-form health survey] and daily step counts [accelerometry]) were compared to norm-based or healthy control scores, respectively. Controls for frailty (Clinical Frailty Score) were non-morbid, age- and gender-matched to survivors. Ninety-one patients were recruited on ICU admission: 41 were contacted for post-discharge assessment, and data were collected from 30 (14 female; mean age, 55.3 yr [95% CI, 48.3–62.3]; mean post-discharge, 576 d [95% CI, 539–614]). Patients’ mean daily step count (5,803; 95% CI, 4,792–6,813) was lower than that in controls (11,735; 95% CI, 10,928–12,542; p < 0.001), and lower in those with preexisting chronic disease than without (2,989 [95% CI, 776–5,201] vs 7,737 [95% CI, 4,907–10,567]; p = 0.013). Physical activity measures (accelerometry, health-related quality of life, and frailty) demonstrated good construct validity across all three tools. Step variability (from SD) was highly correlated with daily steps (r2 = 0.67; p < 0.01) demonstrating a potential boundary constraint.


Subjective and objective measures of physical activity are all informative in ICU survivors. They are all reduced 18 months post-discharge in ICU survivors, and worse in those with pre-admission chronic disease states. Investigating interventions to improve functional capacity in ICU survivors will require stratification based on the presence of premorbidity.

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