Ventilation heterogeneity under mechanical ventilation via mask during anesthetic induction: a randomized trial comparing two ventilation strategies.

Objective.Low tidal volume, limited driving pressure and positive end expiratory pressure (PEEP) are well-accepted lung-protected ventilation strategies. The study aimed to compare driving pressure targeted strategy (PTS) and low tidal volume + PEEP strategy (VPS) in term of ventilation heterogeneity under mechanical ventilation via mask during anesthetic induction.Approach. Patients undergoing anesthesia induction were randomly assign to either PTS or VPS groups. An inspiration pressure of 15 cm H2O and zero PEEP was used in PTS group. A tidal volume of 8 ml kg-1predicted body weight and a PEEP of 5 cm H2O was used in VPS group. The regional lung ventilation was monitored by electrical impedance tomography (EIT). Expiratory tidal volume (TVe), driving pressure, hemodynamics and PaO2/FiO2, and EIT-derived ventilation homogeneity (global inhomogeneity index,GI), the ratio of left/right lung ventilation distribution were calculated.Main results.Finally, 30 patients with PTS and 25 with VPS were analyzed. Compared with spontaneous ventilation, mechanical ventilation via mask caused significant changes in theGI(0.40 ± 0.04 vs 0.48 ± 0.08,P< 0.05). When compared with PTS, VPS was associated with improvedGI(0.52 ± 0.09 vs 0.42 ± 0.03, PTS vs VPS,P< 0.001, power value 0.955), lowerTVe (625.3 ± 192.7 vs 429.1 ± 48.8 ml,P< 0.001), lower driving pressure (15 ± 0 vs 10.5 ± 1.5 cm H2O,P< 0.001), and slightly higher but not statistically different PaO2/FiO2(370.7 ± 90.1 vs 391.1 ± 48.9 mm Hg),P= 0.380).Significance. Mask mechanical ventilation with VPS may improve the lung ventilation inhomogeneity during anesthetic induction when compared with PTS.