Lung Atelectasis Improvement Through Positive End Expiratory Pressure During Anesthetic Induction: a Randomized Trial

General anesthesia may introduce lung atelectasis, which causes an increase in intrapulmonary shunt, and impairs oxygenation, even in the lung-healthy subjects. The magnitude of shunt is correlated with the formation of pulmonary atelectasis. The study aimed to validate that a positive end-expiratory pressure (PEEP) of 10 cmH2O could reduce lung atelectasis, comparing to 0 or 5 cmH2O with limited overdistension. Surgical patients with healthy lungs were randomly assigned to receive 0, 5 or 10 cmH2O PEEP (PEEP0, PEEP5 and PEEP10 groups). Anesthetic induction was performed by certified registered anesthesiologists, during which the patients were mechanically ventilated using the volume-controlled mode. Electrical impedance tomography (EIT) was used to dynamically assess the lung atelectasis during anesthetic induction (spontaneous, mask, and endotracheal intubation ventilation). The primary outcome was the dorsal change of end expiratory lung impedance (△EELI) after 2 mins anesthetic induction. The secondary outcome was driving pressure, EIT-derived ventilation homogeneity, hemodynamics and PaO2/FiO2.