Comparison of the Hemodynamic Safety of Two Common Alveolar Recruitment Manoeuvres With Regard to Cardiac Output in a Surgical Intensive Care Unit

Protective ventilation - combining a low tidal volume (between 6 and 8 ml/kg) and alveolar recruitment (AR) manoeuvres repeated every 30 minutes - is currently the standard of care for decreasing morbidity associated with mechanical ventilation. In contrast, there is no consensus on the type of recruitment manoeuvre, which varies from one centre to another and from one study to another. The investigators intend to compare two currently used AR techniques with regard to their ventilatory efficacy and hemodynamic safety: * An end-tidal plateau at 30 cmH20 for 30 seconds. * An end-tidal plateau at 10 cmH20 above the patient's plateau pressure for 30 seconds, without exceeding 30 cmH20.