title: Evaluating Physical Outcomes in Acute Respiratory Distress Syndrome Survivors: Validity, Responsiveness, and Minimal Important Difference of 4-Meter Gait Speed Test.
abstract: OBJECTIVE
  To examine the reliability, validity, responsiveness, and minimal important difference of the 4-m gait speed test in acute respiratory distress syndrome survivors.
  
  
  METHODS
  Secondary analyses of data from two longitudinal follow-up studies of acute respiratory distress syndrome survivors. Test-retest and inter-rater reliability, construct validity (convergent, discriminant, and known group), predictive validity, and responsiveness were examined. The minimal important difference was estimated using anchor- and distribution-based approaches.
  
  
  METHODS
  A national multicenter prospective study (ARDSNet Long-Term Outcome Study) and a multisite prospective study in Baltimore, MD (Improving Care of Acute Lung Injury Patients).
  
  
  METHODS
  Acute respiratory distress syndrome survivors with 4-m gait speed assessment up to 60 months after acute respiratory distress syndrome (ARDSNet Long-Term Outcome Study, n = 184; Improving Care of Acute Lung Injury Patients, n = 122).
  
  
  METHODS
  Not applicable.
  
  
  RESULTS
  Four-meter gait speed was assessed at 6- and 12-month follow-up (ARDSNet Long-Term Outcome Study) and 36-, 48-, and 60-month follow-up (Improving Care of Acute Lung Injury Patients). Excellent test-retest (intraclass correlation, 0.89-0.99 across studies and follow-up) and inter-rater (intraclass correlation, 0.97) reliability were found. Convergent validity was supported by moderate-to-strong correlations (69% of 32 > 0.40) with other physical function measures. Discriminant validity was supported by weak correlations (86% of 28 < 0.30) with mental health measures. Survivors with impaired versus nonimpaired measures of muscle strength and pulmonary function had significantly slower 4-m gait speed (all but one p < 0.05). Furthermore, 4-m gait speed significantly predicted future hospitalization and health-related quality of life. Gait speed changes were consistent with reported changes in function, supporting responsiveness. The estimated 4-m gait speed minimal important difference was 0.03-0.06 m/s.
  
  
  CONCLUSIONS
  The 4-m gait speed is a reliable, valid, and responsive measure of physical function in acute respiratory distress syndrome survivors. The estimated minimal important difference will facilitate sample size calculations for clinical studies evaluating the 4-m gait speed test in acute respiratory distress syndrome survivors.
authors.affiliation: 1Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD. 2Outcomes After Critical Illness and Surgery (OACIS) Group, The Johns Hopkins University, Baltimore, MD. 3Division of Pulmonary and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 4Division of Pulmonary and Critical Care Medicine, Harborview Medical Center, University of Washington, Seattle, WA. 5Division of Pulmonary, Critical Care & Sleep Medicine, University of Kentucky, Lexington, KY. 6Department of Anesthesiology and Critical Care Medicine, Johns Hopkins University School of Medicine, Baltimore, MD. 7Division of Allergy, Pulmonary, and Critical Care Medicine, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN. 8Geriatric Research, Education and Clinical Center Service, Department of Veterans Affairs Medical Center, Tennessee Valley Healthcare System, Nashville, TN. 9Department of Medicine, Pulmonary and Critical Care Division, Intermountain Medical Center, Murray, UT. 10Center for Humanizing Critical Care, Intermountain Health Care, Murray, UT. 11Psychology Department and Neuroscience Center, Brigham Young University, Provo, UT. 12Department of Physical Medicine and Rehabilitation, Johns Hopkins University School of Medicine, Baltimore, MD.
authors.forename: Kitty S
authors.initials: KS
authors.lastname: Chan
authors.forename: Lisa
authors.initials: L
authors.lastname: Aronson Friedman
authors.forename: Victor D
authors.initials: VD
authors.lastname: Dinglas
authors.forename: Catherine L
authors.initials: CL
authors.lastname: Hough
authors.forename: Peter E
authors.initials: PE
authors.lastname: Morris
authors.forename: Pedro A
authors.initials: PA
authors.lastname: Mendez-Tellez
authors.forename: James C
authors.initials: JC
authors.lastname: Jackson
authors.forename: E Wesley
authors.initials: EW
authors.lastname: Ely
authors.forename: Ramona O
authors.initials: RO
authors.lastname: Hopkins
authors.forename: Dale M
authors.initials: DM
authors.lastname: Needham
mesh_terms: D000328:Adult; D015897:Comorbidity; D005260:Female; D005684:Gait / Q000502:physiology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011788:Quality of Life; D015203:Reproducibility of Results; D012128:Respiratory Distress Syndrome / Q000503:physiopathology*; D012720:Severity of Illness Index; D017741:Survivors