Both lung recruitment maneuver and PEEP are needed to increase oxygenation and lung volume after cardiac surgery

Background: Patients ventilated after cardiac surgery commonly have impaired oxygenation, mainly due to lung collapse. We have previously found that PaO 2 and end-expiratory lung volume (EELV) were increased by a lung recruitment maneuver (LRM) followed by positive end-expiratory pressure (PEEP). The aim of this study was to evaluate whether only PEEP or only a LRM could give similar effects. Methods: Thirty circulatory stable patients (aged 55-79 years) mechanically ventilated after cardiac surgery were randomized to receive LRM (four 10-s insufflations to an airway pressure of 45 cmH 2 O) and zero end-expiratory pressure (LRM-group), PEEP 12 cmH 2 O (PEEP-group) or LRM in combination with PEEP 12 cmH 2 O (LRM + PEEP-group). The set end-expiratory pressure was kept for 75 min. Before, during and after the intervention, EELV (SF 6 washout technique) and blood gases were measured. Results: Initial EELV and PaO 2 were similar in all groups. In the LRM-group, PaO 2 and EELV increased transiently (P < 0.0001), but returned at 5 min to the initial values. In the PEEP-group, PaO 2 did not change but EELV increased to 155 ± 27% of the initial value (P < 0.0001). In the LRM+PEEP-group, PaO 2 and EELV increased to 212 ± 66% and 178 ± 31% of the initial values (P < 0.0001), respectively, and were maintained during PEEP application. Conclusion: In patients ventilated after cardiac surgery: (1) PEEP increased lung volume but not PaO 2 , (2) a lung recruitment maneuver without subsequent PEEP had no sustained effect, and (3) both a lung recruitment maneuver and PEEP were needed to increase and maintain the increased lung volume and PaO 2 .