Driving pressure and mechanical power: new targets for VILI prevention

Abstract

Several factors have been recognized as possible triggers of ventilator-induced lung injury (VILI).The first is pressure (thus the 'barotrauma'), then the volume (hence the 'volutrauma'), finally the cyclic opening-closing of the lung units ('atelectrauma'). Less attention has been paid to the respiratory rate and the flow, although both theoretical considerations and experimental evidence attribute them a significant role in the generation of VILI. The initial injury to the lung parenchyma is necessarily mechanical and it could manifest as an unphysiological distortion of the extracellular matrix and/or as micro-fractures in the hyaluronan, likely the most fragile polymer embedded in the matrix. The order of magnitude of the energy required to break a molecular bond between the hyaluronan and the associated protein is 1.12×10 -16 Joules (J), 70-90% higher than the average energy delivered by a single breath of 1L assuming a lung elastance of 10 cmH 2 O/L (0.5 J). With a normal statistical distribution of the bond strength some polymers will be exposed each cycle to an energy large enough to rupture. Both the extracellular matrix distortion and the polymer fractures lead to inflammatory increase of capillary permeability with edema if a pulmonary blood flow is sufficient. The mediation analysis of higher vs. lower tidal volume and PEEP studies suggests that the driving pressure, more than tidal volume, is the best predictor of VILI, as inferred by increased mortality. This is not surprising, as both tidal volume and respiratory system elastance (resulting in driving pressure) may independently contribute to the mortality. For the same elastance driving pressure is a predictor similar to plateau pressure or tidal volume. Driving pressure is one of the components of the mechanical power, which also includes respiratory rate, flow and PEEP. Finding the threshold for mechanical power would greatly simplify assessment and prevention of VILI.

Effect of Deep Sedation on Mechanical Power in Moderate to Severe Acute Respiratory Distress Syndrome: A Prospective Self-Control Study

“…Mechanical ventilation plays a key role in the treatment of patients with ARDS, although it may cause ventilator-induced lung injury (VILI) [2]. In recent years, it has been found that, during mechanical ventilation of ARDS patients, mechanical power (MP) can be used to evaluate and prevent VILI compared to other mechanical parameters, such as driving pressure, transpulmonary pressure (Ptp), respiratory rate (RR), and positive end-expiratory pressure (PEEP) [3]. It indicates the energy that the ventilator delivers to the entire respiratory system in one minute, expressed as J/min.…”

Recomendaciones de consenso respecto al soporte respiratorio no invasivo en el paciente adulto con insuficiencia respiratoria aguda secundaria a infección por SARS-CoV-2

“…• En caso de usar VMNI, utilizar PEEP altas y presiones de soporte bajas (con el objetivo de obtener un VTe < 9 ml/kg de peso ideal) 31,32 .…”

Mechanical ventilation weaning issues can be counted on the fingers of just one hand: part 2

“…To explain this complicated process in more simple terms: the inspiratory flow conveys a given tidal volume based on the pressure delivered in a unit of time, which is, in turn, determined by the respiratory rate and the I:E ratio (inspiration:expiration ratio). The higher the respiratory rate, the lower the inspiratory time and the higher the flow, resulting in greater pressure applied to the lung parenchyma and an increased risk of VILI [47].…”