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.