Correlation Between Mechanical Power and the Viscoelastic Properties of the Lung

Lung protective ventilation strategy, aiming to decrease ventilation-induced lung injury, is based on 2 major principles: (1) ventilation at a narrow range of volume, with low plateau and driving pressures, while (2) keeping the lung open, to avoid tidal alveolar recruitment/de-recruitment. Mechanical power (MP) was developed as a single value describing energy transfer to the lungs. Energy transfer to the lung parenchyma during ventilation is associated with the viscoelastic properties of the lung. This study aimed to describe the correlation between MP and the viscoelastic properties of the lung.

An exploratory prospective study in an 18-bed mixed ICU of a university-affiliated tertiary hospital. Immediately after percutaneous tracheostomy was performed, 2 inspiratory holds were performed, with 2 different constant flows. Based on the ventilator settings, inspiratory hold measurements [including peak pressure, plateau pressure (P_plat), tidal volume], and resistive elements, viscoelastic properties of the lungs (viscoelastic resistance, R₂; viscoelastic compliance, C₂; and viscoelastic time constant, τ₂) and MP were calculated for each inspiratory hold. Those measurements were compared. MP was correlated with the viscoelastic properties of the lung.

Nine subjects were included in the study. No differences were noted in the viscoelastic properties of the lung between the 2 inspiratory hold measurements. The MP increased in the higher flow inspiratory hold. No correlation was found between either R₂ or C₂ and MP. A moderate negative correlation was found between τ₂ and MP.

MP was found to be negatively correlated with τ₂, but not with R₂ or C₂. The clinical implication of this finding has yet to be defined.