Illustrative fluctuation of airway pressure during three types of lung recruitment maneuvers for intraoperative mechanical ventilation (red lines). (A) “Bag squeezing” using the airway pressure-limiting valve of the anesthesia machine. The airway pressure is difficult to control, possibly resulting in overpressure, with the risk of barotrauma, or values lower than the closing pressure of small airways when controlled mechanical ventilation is resumed, with consequent lung derecruitment. (B) “Stepwise increase of tidal volume” during volume-controlled ventilation. Positive end-expiratory pressure (PEEP) is set at 12 cm H2O, the respiratory frequency at 6 to 8 breaths/min, and tidal volume increased from 8 ml/kg in steps of 4 ml/kg until the target opening pressure (e.g., 30 to 40 cm H2O) is achieved. After three to five breaths at that pressure, the PEEP is kept at 12 cm H2O, tidal volume reduced to 6 to 8 ml/kg, and the respiratory frequency adjusted to normocapnia. (C) Stepwise increase of PEEP at a constant driving pressure of 15 to 20 cm H2O in pressure-controlled ventilation. The PEEP is increased in steps of 5 cm H2O (30 to 60 s per step) up to 20 cm H2O. After three to five breaths at a PEEP level that allows achieving the target inspiratory pressure, PEEP and tidal volume are adjusted to the respective desired levels.
