In ventilated patients open endotracheal suctioning may lead to alveolar derecruitment, which can be monitored by means of functional residual capacity (FRC) measurements. The investigators hypothesized that a recruitment strategy based on FRC measurements would improve oxygenation and regional ventilation after an open endotracheal suctioning manoeuvre.

In mechanically ventilated patients the functional residual capacity will be measured before (baseline) and after an open endotracheal suctioning manoeuvre. Based on these changes patients will be divided into two groups: Group A with more than 94% of baseline FRC, and Group B with less than 94% of baseline FRC. Both groups will be randomized to receive an alveolar recruitment manoeuvre or no alveolar recruitment manoeuvre, leading to four groups. Oxygenation and regional ventilation with electrical impedance tomography will be studied.

Inclusion Criteria:

• ventilated after elective cardiac surgery

Exclusion Criteria:

• hemodynamic instability (eg. intraaortic balloon pump)
• acute lung injury, i.e. PEEP > 10cmH20 or FiO2 > 0.4