Reduction in Postoperative Atelectasis by Continuous Positive Airway Pressure and Low Oxygen Concentration After Endotracheal Extubation.

During general anesthesia, the combination of reduced functional residual capacity (FRC), high inspiratory oxygen fraction (FIO2), and airway closure are the main factors implicated in the atelectasis, shunt and shunt-like effects that account for the majority of the impaired oxygenation seen during general anesthesia.

Previous studies have shown that formation of atelectasis during preoxygenation and induction of anesthesia can be avoided by adding a continuous positive airway pressure (CPAP) followed by a positive end-expiratory pressure (PEEP).During emergence from anesthesia, high concentrations of oxygen predispose to atelectasis formation. Even a recruitment maneuver, followed by ventilation with 100% oxygen with a PEEP/CPAP of 10 cm H2O until extubation, failed to improve postoperative oxygenation compared with that achieved with zero end-expiratory pressure (ZEEP).This failure may have been caused by the presence of lung regions with high oxygen concentrations.

The investigators hypothesized that by inducing and discontinuing anesthesia during CPAP/PEEP and deliberately reducing FIO2 after extubation, postoperative atelectasis would be reduced compared with standard protocols. To test our hypothesis, the investigators studied 1) a control group with no CPAP/PEEP and a FIO2 of 1.0 while breathing spontaneously after extubation, and 2) an intervention group that was on CPAP/PEEP of 6 cmH2O from induction to extubation and that received an FIO2 of 1.0 until extubation and then an FIO2 of 0.3 via a facemask while on CPAP after extubation.