Physiologic Analysis and Clinical Performance of the Ventilatory Ratio in Acute Respiratory Distress Syndrome

Abstract

Rationale and Objectives: Pulmonary dead space fraction is an independent predictor of mortality in acute respiratory distress syndrome (ARDS). Yet, it is seldom utilized in practice. The Ventilatory ratio is a simple bedside index that can be calculated using routinely measured respiratory variables and is a measure of impaired ventilation. Ventilatory ratio is defined as [minute ventilation (mL/min) * arterial PCO2 (mmHg)]/[predicted body weight * 100 * 37.5]. The relation of Ventilatory Ratio with in ARDS is currently unknown. Methods: First, in a single-center, prospective observational study of ARDS, we tested the association of with Ventilatory Ratio. With in-hospital mortality as the primary outcome and ventilator-free days as the secondary outcome, we tested the role of Ventilatory Ratio as an outcome predictor. The findings from this study were further verified in secondary analyses of two NHLBI ARDS Network randomized controlled trials. Measurements and Main Results: Ventilatory Ratio positively correlated with . Ordinal groups of Ventilatory Ratio had significantly higher . Ventilatory Ratio was independently associated with increased risk of mortality after adjusting for PaO2/FiO2, and PEEP (OR 1.51, p = 0.024) and after adjusting for APACHE II score (OR 1.59, p=0.04). These findings were further replicated in secondary analyses of two separate NHLBI randomized controlled trials. Conclusions: Ventilatory Ratio correlates well with in ARDS and higher values at baseline are associated with increased risk of adverse outcomes. These results are promising for the use of Ventilatory Ratio as a simple bedside index of impaired ventilation in ARDS.