The aim of the study is to compare two different ventilation modes in complicated postcardiac surgery patients, who need ventilatory support during weaning phase, in the Cardiothoracic Intensive Care Unit. The two different ventilation modes are Neuronally Adjusted Ventilatory Assist (NAVA) and Pressure Support ventilation. NAVA ventilation mode have been introduced a couple of years ago as an alternative to pressure support. The advantage of NAVA mode compared to pressure support is a better synchrony between patient and ventilator in the inspired and expired phases. Maybe there are also physiological advantages of the NAVA mode, which we want to study in the present study.