Ventilator-Free Day Outcomes Can Be Misleading

Area of Science:

• Critical Care Medicine
• Clinical Trials Methodology
• Biostatistics

Background:

• Acute respiratory distress syndrome (ARDS) frequently necessitates invasive mechanical ventilation.
• Mortality and duration of mechanical ventilation are key outcomes in ARDS research.
• Ventilator-free days (VFDs) have been proposed as a composite outcome to capture both mortality and ventilation duration.

Purpose of the Study:

• To analyze the construction of the VFD outcome.
• To highlight potential misleading interpretations of VFDs in clinical practice.
• To compare statistical methods for analyzing mechanical ventilation outcomes.

Main Methods:

• Proposed the isoventilator-free day curve concept.
• Utilized analytical development to illustrate VFD interpretation variability.
• Compared Student t test, Wilcoxon rank-sum test, and Gray test using hypothetical and real data.

Main Results:

• A median VFD value can mask diverse combinations of mortality rates and mechanical ventilation durations.
• The Student t test was sensitive to changes in the time horizon, unlike the Wilcoxon rank-sum test.
• The Gray test, accounting for death as a competing event, proved more relevant than t tests or Wilcoxon tests in detecting differences in ventilation duration.

Conclusions:

• The use of VFDs as a primary outcome in ARDS research presents significant drawbacks.
• Alternative analytical methods focusing on time to extubation are recommended for more accurate outcome assessment.
• The Gray test offers a more robust approach for analyzing mechanical ventilation data when death is a competing risk.