Mechanical power made simple: validating a simplified calculation of mechanical power in preterm lungs.

Abstract

The incidence of chronic lung disease is increasing, suggesting a need to explore novel ways to understand ventilator induced lung injury (VILI) in preterm infants. Mechanical power (MP) is a unifying measure of energy transferred to the respiratory system and a proposed determinant of VILI. The gold-standard method for calculating MP (geometric method) is not feasible in the clinical setting. This has prompted the derivation of simplified equations for calculating MP. To validate the agreement between a simplified calculation of MP (MPSimple) and the true MP calculated using the geometric method (MPRef). MPSimple and MPRef was calculated in mechanically ventilated preterm lambs (n = 71) and the agreement between both measureswas determined using intraclass correlation coefficients (ICC), linear regression, and Bland-Altman analysis. A strong linear relationship (adjusted R2 = 0.98), and excellent agreement (ICC = 0.99, 95% CI = 0.98-0.99) between MPSimple and MPRef was demonstrated. Bland-Altman analysis demonstrated a negligible positive bias (mean difference = 0.131 J/min·kg). The 95% limits of agreement were -0.06 to 0.32 J/min·kg. In a controlled setting, there was excellent agreement between MPSimple and gold-standard calculations. MPSimple should be validated and explored in preterm neonates to assess the cause-effect relationship with VILI and neonatal outcomes. Mechanical power (MP) unifies the individual components of ventilator induced lung injury (VILI) and providesan estimate of total energy transferred to the respiratory system during mechanical ventilation. As gold-standard calculations of mechanical power at the bedside are not feasible, alternative simplified equations have been proposed. In this study, MP calculated using a simplified equation had excellent agreement with true MP in mechanically ventilated preterm lambs. These results lay foundations to explore the role of MP in neonatal VILI and determine its relationship with short and long term respiratory outcomes.