Estimating the Damaging Power of High-Stress Ventilation

Abstract

Redirection of our clinical attention from the pressures and volumes of the individual cycle to the broader and more inclusive considerations of energy load and power has untapped potential to reduce iatrogenic risk from ventilation (ie, ventilator-induced lung injury). Power is the product of breathing frequency and inflation energy per breath. Yet, while feasible to calculate at the bedside, measuring total power may not prove to be precise enough for accurate prediction of ventilator-induced lung injury, even if normalized to lung capacity (ie, specific power). The same power value can be reached by a multitude of frequency and tidal volume combinations, not all of which carry equal risk of damage. If some arbitrary level of alveolar pressure were accepted as a sharply defined hazard boundary, a rather straightforward geometric analysis theoretically would allow partitioning of overall tidal energy into components above and below a damage threshold. In this discussion, we introduce the concept of quantitative power partitioning and illustrate how tidal energy and power might be deconstructed into their key parts.

Influence of age, mechanical power, its fragments and components on the mortality rate in SARS-CoV-2 patients undergoing mechanical ventilation

“…The normalization of Mechanical Power value as a safety threshold for the prevention of VILI would depend on the knowledge of lung volumes and its distribution, as well as the Stress and Strain on the pulmonary heterogeneity. [14][15][16][17][18][19][20][21][22][23][24][25][26][27] An elevated Mechanical Power regardless of the combination of its components can lead to VILI 13 especially when it exceeds 12J/min, whereas over 17J/min it is associated with a higher mortality rate [19][20][21][22][23][24][25][26][27][28] The safety threshold for mechanical power values beyond which VILI is inevitable [11][12][13][14] and whether a Mechanical Power-based mechanical ventilation strategy can improve patients' clinical status 14 are still unknown as it is unclear the contribution of each ventilation parameter for the generation of such pulmonary injury.…”

“…Comprised of plateau pressure, driving pressure, PEEP, tidal volume, flow, resistance, elastance and respiratory rate, [13][14] mechanical power depicts the energy transferred to the respiratory system by the mechanical ventilator 13 during a certain period in Joule per minute (J/min). [11][12][13][14][15] Even though there is a tendency to replace the concepts based on tidal volume and pressures in the tidal cycle for the understanding of mechanical power as generator of VILI, its predictive precision is still alleged, [16][17] given there are patients submitted to potential VILI generating tidal volume and pressures that survive, making the correlation between ventilatory strategy and clinical status questionable. 18 However, lower levels of mechanical power are desired, 19 as it unifies the components of the mechanical ventilation in an attempt to build a unity of indicators that reflect VILI.…”

“…The product of the tidal volume per plateau pressure defines the total elastic power, 17 subdivided into dynamic and static elastic powers. The dynamic one is equal to the energy necessary to inflate the lungs, whereas the static one is the energy required to balance out the potential energy stored in the respiratory system by the PEEP.…”

“…The dynamic one is equal to the energy necessary to inflate the lungs, whereas the static one is the energy required to balance out the potential energy stored in the respiratory system by the PEEP. 21 The total inflation energy, that is, the mechanical power is equal to the total elastic power plus the total kinetic power, 17 which is the energy spent on overcoming the airway and tissue resistance to the flow. 21 The product of these equations by the respiratory rate and by the conversion constant 0.098 results in Joules per minute.…”

Personalized mechanical ventilation in acute respiratory distress syndrome

“…At present, there is a lack of agreement on the computation underpinning the calculation of mechanical power and determinants (PEEP levels, frequency, and lung size) that should be taken into consideration, and therefore, personalization is not possible. Although readily measured at the bedside, its value in VILI prediction remains controversial [ 40 – 42 ].…”