Mechanical Power and Development of Ventilator-induced Lung Injury

Abstract

Background The ventilator works mechanically on the lung parenchyma. The authors set out to obtain the proof of concept that ventilator-induced lung injury (VILI) depends on the mechanical power applied to the lung. Methods Mechanical power was defined as the function of transpulmonary pressure, tidal volume (TV), and respiratory rate. Three piglets were ventilated with a mechanical power known to be lethal (TV, 38 ml/kg; plateau pressure, 27 cm H2O; and respiratory rate, 15 breaths/min). Other groups (three piglets each) were ventilated with the same TV per kilogram and transpulmonary pressure but at the respiratory rates of 12, 9, 6, and 3 breaths/min. The authors identified a mechanical power threshold for VILI and did nine additional experiments at the respiratory rate of 35 breaths/min and mechanical power below (TV 11 ml/kg) and above (TV 22 ml/kg) the threshold. Results In the 15 experiments to detect the threshold for VILI, up to a mechanical power of approximately 12 J/min (respiratory rate, 9 breaths/min), the computed tomography scans showed mostly isolated densities, whereas at the mechanical power above approximately 12 J/min, all piglets developed whole-lung edema. In the nine confirmatory experiments, the five piglets ventilated above the power threshold developed VILI, but the four piglets ventilated below did not. By grouping all 24 piglets, the authors found a significant relationship between the mechanical power applied to the lung and the increase in lung weight (r2 = 0.41, P = 0.001) and lung elastance (r2 = 0.33, P < 0.01) and decrease in Pao2/Fio2 (r2 = 0.40, P < 0.001) at the end of the study. Conclusion In piglets, VILI develops if a mechanical power threshold is exceeded.

Driving pressure and mechanical power: new targets for VILI prevention

“…Indeed, the effects of respiratory rate on VILI have been described in experimental animals (27,28). In particular, when we applied a strain greater than 2, which invariably leads to death when delivered at a rate of 15 bpm, we found a lack of injurious effect if delivered at 3 or 6 bpm (29). The relevance of respiratory rate underlines another possible scenario: indeed, in analogy with materials fatigue, it may be possible that damage occurs only after a given number of stress and strain cycles have been delivered and generated into the lung (i.e., VILI below the stress at rupture requires time).…”

Optimal mechanical ventilation strategies to minimize ventilator-induced lung injury in non-injured and injured lungs

“…Nevertheless, only a single respiratory cycle is measured when performing this calculation. To ascertain what happens over a longer period, power (energy multiplied by respiratory rate) is measured instead [22]. In this line, a recent study reported that VILI may develop if mechanical power exceeds 12 J/min.…”

Respiratory rate and peak inspiratory pressure, new targets from the LUNG SAFE study analysis or physiopathological artifacts?

“…As a concept, the less you transfer energy to the injured lungs, the better it is. Even if this concept is mainly established in animal model (10), there are some arguments in a recent second analysis of the two randomized clinical trials PROSEVA and ACURASY of the impact of mechanical power on prognosis (11).…”