Ventilation of poorly aerated dependent lung regions, which can promote the local concentration of mechanical stresses, was the predominant functional behavior in surfactant-depleted lung. Potential tidal recruitment of atelectatic lung regions involved a smaller fraction of the imaged lung. Significant ventilation redistribution to aerated lung regions places these at risk of increased stretch injury.

The parallel changes in ELV and EELV with PEEP in healthy and surfactant-depleted lungs support the clinical value of ELV measurement as a bedside tool to estimate dynamic changes in EELV in children and infants.

Individualised PVV based on a pre-recorded spontaneous breathing pattern provides adequate gas exchange and promotes a level of lung protection. This ventilation modality could be of benefit during prolonged anaesthesia, in which assisted ventilation is not possible because of the absence of a respiratory drive.

Background: Although high inspired oxygen fraction (FiO 2) is common practice in pediatric anaesthesia, there is lack of evidence for affects on postoperative lung function. Therefore, we compared postoperative changes in lung volume, ventilation heterogeneity and respiratory mechanics while ventilating anaesthetised children with low or high FiO 2. Methods: In a double-blinded, randomized, controlled trial, children scheduled for elective surgery were randomly assigned 100% FiO 2 (Group H) or 80% FiO 2 (Group L) during anaesthesia induction and emergence, while anaesthesia was maintained with either FiO 2 of 80% (Group H) or 35% (Group L). During spontaneous breathing, we measured functional residual capacity (FRC) and lung clearance index (LCI) by multiple-breath nitrogen washout, airway resistance and respiratory tissue elastance by forced oscillations preoperatively (M1), after discharge from the recovery room (M2) and at day 1 postoperatively (M3). Secondary outcomes were the occurrence of respiratory complications, post-operative nausea and vomiting and surgical site infection at 30 days postoperatively. Results: FRC decreased in Group H at M2 (-14.7% [-21.0,-8.3] 95% CI, p=0.008) but normalized at M3. Ventilation inhomogeneity (LCI) increased in both groups at M2 but remained elevated only in Group H at M3 (6.3% [-0.3, 12.9%], p=0.023). No differences in respiratory mechanical parameters or in secondary outcomes were observed. Conclusions: High FiO 2 decreases lung volume in the immediate postoperative period with long-lasting enhancement in lung heterogeneity. This result, in addition to the wellestablished harmful effects of hyperoxia, supports the avoidance of high FiO 2 during anaesthesia management of children with normal lungs.