Evaluating Physical Outcomes in Acute Respiratory Distress Syndrome Survivors: Validity, Responsiveness, and Minimal Important Difference of 4-Meter Gait Speed Test

Crit Care Med. 2016 May;44(5):859-68. doi: 10.1097/CCM.0000000000001760.


Objective: To examine the reliability, validity, responsiveness, and minimal important difference of the 4-m gait speed test in acute respiratory distress syndrome survivors.

Design: 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.

Setting: 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).

Patients: 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).

Interventions: Not applicable.

Measurements and main 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.

Publication types

  • Multicenter Study
  • Research Support, N.I.H., Extramural

MeSH terms

  • Adult
  • Comorbidity
  • Female
  • Gait / physiology*
  • Humans
  • Longitudinal Studies
  • Male
  • Middle Aged
  • Observer Variation
  • Predictive Value of Tests
  • Prospective Studies
  • Quality of Life
  • Reproducibility of Results
  • Respiratory Distress Syndrome / physiopathology*
  • Severity of Illness Index
  • Survivors*