Postoperative respiratory complication is a common complication that occurs in 6% of patients after cardiac surgery and increases morbidity and mortality and hospital length of stay. Diaphragmatic dysfunction (DD) is one of the main risk factors for post-operative respiratory distress syndrome. It alters the ventilatory mechanical function of patients and promotes pneumonia. In the literature, risk factors included older age, diabetes, harvesting of a mammary artery, intraoperative ice solution using, prolonged cardiopulmonary bypass and intra-operative phrenic nerve injury.

Ultrasonography using the two-dimensional (2D) mode is a diagnosis tool for DD. For patients with DD, ultrasound criteria are: 1) an excursion during quiet breathing < 9 mm for woman and < 10 mm for man, 2) an excursion after sniff test < 16 mm for woman and < 18 mm for man and 3) an excursion during deep breathing < 37 mm for woman and < 47 mm for man. A paradoxical diaphragmatic ascent may also be observed during inspiration.

DD may be transient, linked to mechanical factors such as pain, the presence of pleural and mediastinal drains, lying down or sternotomy; with recovery from 5 postoperative days. It may be more prolonged (persistent after 7 days) in connection with a partial or complete phrenic nerve injury and / or diaphragmatic devascularization after mammary artery harvesting.

The aim of this prospective study is to determine the incidence of persistent DD after cardiac surgery.

Diaphragmatic amplitude will be assessed by ultrasonography during quiet breathing and after sniff test, before the surgery and at day 7 post-surgery in all patients.

Patients with persistent DD at day 7 post-surgery will have additional Respiratory Functional Explorations.

Inclusion Criteria:

• Patients undergoing cardiac surgery requiring sternotomy
• Consent for participation
• Affiliation to the social security system

Exclusion Criteria:

• Contraindication to preoperative respiratory functional explorations
• Pregnant or breastfeeding women
• Patients under protection of the adults (guardianship, curators or safeguard of justice)
• Communication difficulties or neuropsychiatric disorder

150 patients undergoing cardiac surgery