Ventilator-related causes of lung injury: the mechanical power

Abstract

We hypothesized that the ventilator-related causes of lung injury may be unified in a single variable: the mechanical power. We assessed whether the mechanical power measured by the pressure–volume loops can be computed from its components: tidal volume (TV)/driving pressure (∆P_aw), flow, positive end-expiratory pressure (PEEP), and respiratory rate (RR). If so, the relative contributions of each variable to the mechanical power can be estimated. Computed and measured mechanical powers were similar at 5 and 15 cmH₂O PEEP both in normal subjects and in ARDS patients (slopes = 0.96, 1.06, 1.01, 1.12 respectively, R² > 0.96 and p < 0.0001 for all). The mechanical power increases exponentially with TV, ∆P_aw, and flow (exponent = 2) as well as with RR (exponent = 1.4) and linearly with PEEP. The mechanical power equation may help estimate the contribution of the different ventilator-related causes of lung injury and of their variations. The equation can be easily implemented in every ventilator’s software.