Adaptive mechanical ventilation with automated minimization of mechanical power—a pilot randomized cross-over study

BACKGROUND: Adaptive mechanical ventilation automatically adjusts respiratory rate (RR) and tidal volume (V(T)) to deliver the clinically desired minute ventilation, selecting RR and V(T) based on Otis’ equation on least work of breathing. However, the resulting V(T) may be relatively high, especially in patients with more compliant lungs. Therefore, a new mode of adaptive ventilation (adaptive ventilation mode 2, AVM2) was developed which automatically minimizes inspiratory power with the aim of ensuring lung-protective combinations of V(T) and RR. The aim of this study was to investigate whether AVM2 reduces V(T), mechanical power, and driving pressure (ΔP(stat)) and provides similar gas exchange when compared to adaptive mechanical ventilation based on Otis’ equation. METHODS: A prospective randomized cross-over study was performed in 20 critically ill patients on controlled mechanical ventilation, including 10 patients with acute respiratory distress syndrome (ARDS). Each patient underwent 1 h of mechanical ventilation with AVM2 and 1 h of adaptive mechanical ventilation according to Otis’ equation (adaptive ventilation mode, AVM). At the end of each phase, we collected data on V(T), mechanical power, ΔP, PaO(2)/FiO(2) ratio, PaCO(2), pH, and hemodynamics. RESULTS: Comparing adaptive mechanical ventilation with AVM2 to the approach based on Otis’ equation (AVM), we found a significant reduction in V(T) both in the whole study population (7.2 ± 0.9 vs. 8.2 ± 0.6 ml/kg, p < 0.0001) and in the subgroup of patients with ARDS (6.6 ± 0.8 ml/kg with AVM2 vs. 7.9 ± 0.5 ml/kg with AVM, p < 0.0001). Similar reductions were observed for ΔP(stat) (whole study population: 11.5 ± 1.6 cmH(2)O with AVM2 vs. 12.6 ± 2.5 cmH(2)O with AVM, p < 0.0001; patients with ARDS: 11.8 ± 1.7 cmH(2)O with AVM2 and 13.3 ± 2.7 cmH(2)O with AVM, p = 0.0044) and total mechanical power (16.8 ± 3.9 J/min with AVM2 vs. 18.6 ± 4.6 J/min with AVM, p = 0.0024; ARDS: 15.6 ± 3.2 J/min with AVM2 vs. 17.5 ± 4.1 J/min with AVM, p = 0.0023). There was a small decrease in PaO(2)/FiO(2) (270 ± 98 vs. 291 ± 102 mmHg with AVM, p = 0.03; ARDS: 194 ± 55 vs. 218 ± 61 with AVM, p = 0.008) and no differences in PaCO(2), pH, and hemodynamics. CONCLUSIONS: Adaptive mechanical ventilation with automated minimization of inspiratory power may lead to more lung-protective ventilator settings when compared with adaptive mechanical ventilation according to Otis’ equation. TRIAL REGISTRATION: The study was registered at the German Clinical Trials Register (DRKS00013540) on December 1, 2017, before including the first patient.