Mechanical power in AVM-2 versus conventional ventilation modes in various ARDS lung models. Bench study

Abstract

Introduction Mechanical power has been linked to ventilator induced lung injury and mortality in acute respiratory distress syndrome (ARDS). Adaptive Ventilator Mode-2 is a closed-loop pressure-controlled mode with an optimal targeting scheme based on the inspiratory power equation that adjusts the respiratory rate and tidal volume to achieve a target minute ventilation. Conceptually, this mode should reduce the mechanical power delivered to the patients and thus reduce the incidence of ventilator induced lung injury. Methods A bench study using a lung simulator was conducted. We constructed three passive single compartment ARDS models (Mild, Moderate, Severe) with compliance of 40, 30, 20 ml/cmH2O respectively, and resistance of 10 cmH2O/L/s, with IBW 70 kg. We compared three different ventilator modes: AVM-2, Pressure Regulated Volume Control (PRVC), and Volume Controlled Ventilation (VCV) in six different scenarios: 3 levels of minute ventilation 7, 10.5, and 14 Lit/min (Experiment 1, 2, and 3 respectively), each with 3 different PEEP levels 10, 15, and 20 cmH2O (Experiment A, B, and C respectively) termed 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B, 3C respectively for a total of 81 experiments. The AVM-2 mode automatically selects the optimal tidal volume and respiratory rate per the dialed percent minute ventilation with an I:E ratio of 1:1. In the PRVC and VCV (constant flow) we selected target tidal volume 6ml/kg/IBW (420 ml) and respiratory rate adjusted to match the minute ventilation for the AVM-2 mode. I:E ratio was kept 1:2. The mechanical power delivered by the ventilator for each mode was computed and compared between the three modes in each experiment. Statistical analysis was done using Kruskal-Wallis test to analyze the difference between the three modes, post HOC Tukey test was used to analyze the difference between each mode where P < 0.05 was considered statistically significant. The Power Compliance Index was calculated and compared in each experiment. Multiple regression analysis was performed in each mode to test the correlation of the variables of mechanical power to the total calculated power. Results There were statistically significant differences (P < 0.001) between all the three modes regarding the ventilator delivered mechanical power. AVM-2 mode delivered significantly less mechanical power than VCV which in turn was less than PRVC. The Power Compliance index was also significantly lower (P < 0.01) in the AVM-2 mode compared to the other conventional modes. Multiple regression analysis indicated that in AVM-2 mode, the driving pressure (P = 0.004), tidal volume (P < 0.001), respiratory rate (P = 0.011) and PEEP (P < 0.001) were significant predictors in the model. In the VCV mode, the respiratory rate (P 0< 0.001) and PEEP (P < 0.001) were significant predictors, but the driving pressure was a non-significant predictor (P = 0.08). In PRVC mode, the respiratory rate (P < 0.001), PEEP (P < 0.001) and driving pressure (P < 0.001) were significant predictors. Conclusion AVM2 mode delivered less mechanical power compared to two conventional modes using low tidal volume in an ARDS lung model with different severities. This might translate to the reduction of the incidence of ventilator induced lung injury. Results need to be validated in clinical studies.

Correlations of mechanical power and its components with age and its interference in the outcome of SARS-CoV-2 in subjects undergoing pressure-controlled ventilation

“…20 Similar findings in a bench study that showed that showed the AVM-2 mode delivered significantly less mechanical power than VCV, which in turn was less than PCV in various ARDS severity. 21 The impact of mechanical power is consistent and independent of the presence of ARDS and the use of neuromuscular blockers, and even with the maintenance of tidal volume and driving pressure at low values, it was associated with worse outcomes, which suggests that mechanical power adds information that go beyond just the tidal volume and driving pressure. 22 Regarding the comparison between survival and death outcomes, except for PEEP, Ve, PRresist and resistance, the mean values of all the other components showed significance in relation to the outcome in the isolated assessment.…”

“…Thus, in order to recognize if the mechanical power is increased by iatrogenesis in the ventilation adjustments, or if it is increased by the severity of ARDS, or even if it is related to incurability by VILI, we would possibly have to somehow index the mechanical power with the compliance or elastance. 21 Theoretically, a well aerated lung with better compliance will require less mechanical power i.e. lower Power Compliance Index (higher Power Elastance Index), versus a non-aerated lung with poorer compliance will require higher mechanical power i.e.…”

A comparative analysis of mechanical power and Its components in pressure-controlled ventilation mode and AVM-2 mode

“…This finding confirms our previous bench work where we found lower mechanical power, and PCI between AVM-2 compared to conventional VCV and PCV in an ARDS lung model with different severities. 13 As Marini and colleagues 18 suggested, normalizing or indexing the mechanical power to the compliance of the lung or the amount of aerated lung might be more meaningful than mechanical power alone, as it represents the amount of energy delivered to a specific injured unit. Coppola and colleagues 22 conducted a retrospective study in ARDS patients and found that the mechanical power alone did not correlate with mortality, however, mechanical power normalized to the compliance or to the amount of well-aerated tissue is independently associated with mortality.…”

“…We found a significant decrease in mechanical power, tidal volume, and inspiratory pressures. 13 In this study, we intended to analyze the differences between the established PCV and the innovative AVM-2 modes to measure disparities in mechanical power, including its key components: PEEP work, tidal work, elastic work, resistive work, inspiratory work, total work, tidal volume, tidal volume/IBW, and driving pressure. We hypothesized that AVM-2 would deliver less work (J) and mechanical power (J/min) compared to PCV, suggestive of greater lung protection.…”

Alveolar mechanics: A new concept in respiratory monitoring

“…Adaptive Ventilation Mode-2 (AVM-2) is a closed loop mode of ventilation with an optimal targeting scheme using the concept of mean inspiratory power (sum of the resistive and tidal power) that takes the VD into account in its algorithm for targeting the optimal VT and respiratory rate. 39,40 -Alveolar resistance…”