Dynamic predictors of VILI risk: beyond the driving pressure

Excerpt

As currently implemented, lung protective ventilation concentrates on certain static characteristics of the individual tidal cycle—tidal volume (TV), plateau pressure, PEEP, and recently, on the difference between the latter two static values, the driving pressure (DP) [1]. The rationale for focusing on any of these has been based primarily on concept, focused animal experiments, and clinical data supporting their relative importance. However, the physical process that causes ventilator-induced lung injury (VILI) has been difficult to pin down. It is clear that mechanical forces, lung patho-anatomy and non-ventilatory characteristics each contribute. Excessive stretch, strain, and tidal opening and closure may all be important, but the precise mechanism through which they act remains unclear. Dynamic characteristics—frequency, flow rate, strain rate—have recently been emphasized as key determinants of whether the ‘static’ variables inflict injury [2]. In this issue, Gattinoni and colleagues present an elegant and persuasive argument that energy delivered per unit time (‘power’) is a unifying entity into which most key ventilator settings and forces relevant to VILI can be channeled, thus providing a “composite index” by which to translate this insight into clinical practice [3]. As clearly stated by the authors themselves, the mechanical power concept in the genesis of VILI is not new. Rather, the novelty of this work lies in proposing and validating a mathematical description of machine power responsive to the relative contributions of its bedside-adjustable components (TV, frequency, ΔP _aw, PEEP, I:E, flow). This interesting and provocative proposal urges a potentially important conceptual shift in our thinking that deserves to be carefully examined. …