Role of static and dynamic driving airway pressure in the development of ventilator-induced lung injury

Abstract

Introduction: Driving airway pressure, the difference between plateau (end of an inspiratory pause) and end-expiratory airway pressure, can be an independent predictor of ventilator-induced lung injury (VILI) [1]. However, during ongoing mechanical ventilation, (dynamic) end-inspiratory airway pressure exceeds (static) plateau airway pressure, especially when inspiratory flows are very high [2]. Thus, for the same static driving airway pressure, different dynamic driving airway pressures can be reached. Objectives: To compare the role of static and dynamic driving airway pressures in the development of VILI. Methods: Sixteen healthy piglets were anesthetized, paralyzed and mechanically ventilated for 54 hours with no positive end-expiratory pressure. Animals were divided into two groups that were matched for static driving airway pressure (deltaPAW,stat), defined as above, but not for dynamic driving airway pressure (deltaPAW,dyn), defined as the difference between airway pressure recorded when flow zeroed immediately after an end-inspiratory occlusion (P1) and end-expiratory airway pressure. Lower and higher dynamic driving airway pressures were obtained by using lower or higher inspiratory flows. Respiratory rate was always 15 breath-per-minute. VILI was diagnosed if final lung weight (measured with a balance) exceeded initial lung weight (measured with computed tomography), as for edema. Data were compared between the two groups with Student's t and Fisher's Exact tests. Results: The two groups of animals were ventilated with similar static but different dynamic driving airway pressures (Table 66). Incidence of VILI was 25 % among animals ventilated with lower and 75 % among those ventilated with higher dynamic driving airway pressure (p = 0.13). On average, lung weight decreased over time (-56 +/- 60 g) in the former group whereas it increased (98 +/- 166 g) in the latter group (p = 0.04). Mortality at 54 hours was 13 % among animals ventilated with lower and 63 % among those ventilated with higher dynamic driving airway pressure (p = 0.12). Conclusions: For the same static driving airway pressure, higher dynamic driving airway pressures may increase the incidence of (fatal) ventilator-induced lung injury.