Cardiac Surgery and Diaphragm Function

Diaphragm dysfunction is common after cardiac surgery and may delay weaning from mechanical ventilation and cause respiratory distress. The investigators' main objective is to determine the incidence of diaphragm dysfunction ( using the non-invasive ultrasonic method by calculating the inspiratory diaphragmatic thickening fraction) in a selected population of cardiac surgery patients during weaning from mechanical ventilation. The second endpoints are to determine the associated risk factors to post-operative diaphragm weakness and the consequence on the patient outcome.