Applying positive end-expiratory pressure to facemask ventilation improves post-induction lung atelectasis: a three-arm randomized controlled trial

Induction of general anesthesia is associated with rapid-onset lung atelectasis, which increases intrapulmonary shunt and potentially impairs oxygenation. We aimed to evaluate whether applying positive end-expiratory pressure (PEEP) to facemask ventilation during induction of general anesthesia can reduce post-induction lung atelectasis. In this single-center, three-arm randomized controlled trial, one hundred and twenty ASA I-II patients undergoing elective non-cardiothoracic cancer surgery under general anesthesia were randomly assigned into three groups. Facemask ventilation was initiated in volume-controlled mode with preassigned PEEP levels (0, 5, or 10 cmH2O) after anesthetic administration. Electrical impedance tomography (EIT) was used to continuously assess lung atelectasis during induction of general anesthesia, including baseline spontaneous breathing, facemask ventilation, and post-intubation mechanical ventilation. The primary outcome was the dorsal change in end-expiratory lung volume (△EELV) 2 min after endotracheal intubation. The secondary outcomes included driving pressure, EIT-derived ventilation homogeneity, systemic hemodynamics, and PaO2/FiO2 ratio. Atelectasis (defined as △EELV < 0) occurred in both the PEEP0 and PEEP5 groups during facemask ventilation [-58.8% (-110.4%, 4.0%) and − 34.2% (-200%, 19.2%), respectively] and after induction [-26.9% (-127.4%, 33.6%) and − 33.2% (-52.8%, 5.0%), respectively], but not in the PEEP10 group [25.3% (-12%, 104.7%)]. Facemask ventilation with 10 cmH2O PEEP demonstrated better dorsal lung recruitment than both lower PEEP levels (P < 0.05), reduced post-induction driving pressure (P < 0.05), and improved ventilation homogeneity (P < 0.05). Hemodynamics and PaO2/FiO2 ratio were comparable among the three groups. Use of 10 cmH2O PEEP during induction of general anesthesia effectively mitigated dorsal lung collapse by optimizing respiratory mechanics without inducing overdistension and hemodynamic compromise. It is worth investigating whether this improvement can be extended to the postoperative period. NCT06900426 (registered at clinicaltrials, principal investigator: Jun Zhang, registration date: March 17, 2025).