Mechanical power in AVM-2 versus conventional ventilation modes in a normal lung model: A bench study

Introduction Recent studies suggested that the energy delivered by the mechanical ventilator to the lungs termed the mechanical power can induce and increase the risks of ventilator induced lung injury. The components of the mechanical power include the variables delivered by the ventilator: tidal volume, respiratory rate, inspiratory flow, airway pressure. Adaptive Ventilator Mode-2 (AVM-2) is a 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. This mode conceptually should reduce the mechanical power delivered to the patients and thus reduce the incidence of ventilator induced lung injury. Methodology A bench study using a lung simulator (TTL, Michigan Instruments, Michigan, USA) was conducted. We constructed a passive single compartment normal respiratory mechanics model with compliance of 50 ml/cmH2O, and resistance of 10 cmH2O/L/s, with IBW 70 kg. We compared three different ventilator modes: Adaptive Ventilation Mode-2 (AVM-2), Pressure Regulated Volume Control (PRVC), and Volume Controlled Ventilation (VCV) in four different scenarios: 2 levels of minute ventilation 7 and 10.5 Lit/min (Experiment 1 and 2 respectively), each with 2 different PEEP levels 5 and 10 cmH2O (Experiment A and B respectively) termed Experiments 1A, 1B, 2A, and 2B respectively. 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, VCV 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 to avoid intrinsic PEEP. The study was conducted using a bellavista™ 1000 e Ventilator (Vyaire Medical, Illinois, USA). 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 with the confidence intervals, P < 0.05 was considered statistically significant. Results There were statistically significant differences between all the three modes regarding the ventilator delivered mechanical power. The AVM-2 mode delivered significantly less mechanical power than VCV which in turn was less than PRVC. Experiment 1A: AVM-2 8.76 土 0.05, VCV 9.78 土 0.04, PRVC 10.82 土 0.08, P < 0.001 Experiment 1B: AVM-2 11.27 ± 0.09 VCV 12.81 ± 0.05, PRVC 13.88 ± 0.06, P < 0.001. Experiment 2A: AVM-2 14.76 ± 0.05, VCV 15.79 ± 0.05, PRVC 18.29 ± 0.07, P < 0.001, Experiment 2B: AVM-2 18.76 ± 0.04, VCV 20.56 ± 0.04, PRVC 21.17 土 0.03, P < 0.001. Discussion AVM2 mode delivered less mechanical power compared to two conventional modes using low tidal volume in a normal lung model. This might reduce the incidence of ventilator induced lung injury. Results need to be validated in more clinical studies.