Sonographic Monitoring of Diaphragm after Cardiac Surgery

The enrolled patients will undergo to a sonographic measurement of diaphragmatic motion (right and left hemidiaphragmatic excursion) and diaphragmatic thickness (on the right side) the day before surgery, during the weaning trial, the day after the weaning trials and at the patient discharge. All patients will be evaluated in a semi-recumbent position, with the head of the bed elevated at an angle between 30° and 45°. Ultrasound will be performed using a SonoSite ultrasound system equipped with a 5 MHz convex probe for the subcostal approach and a 13 MHz linear probe for the approach in the zone of apposition. To evaluate diaphragmatic displacement, the probe is places immediately below the right or left costal margin, between the mid-clavicular and anterior axillary lines, using liver or spleen as acoustic windows. The probe is directed medially, cephalad and dorsally, so that the ultrasound beam reaches perpendicularly the posterior third of the corresponding hemi-diaphragm. Diaphragm is identified as a hyperechoic line, produced by the pleura tighten adherent to the muscle.The two dimensional (2D) mode is initially used to obtain the best approach and select the exploration line. The M-mode is then used to display the motion of the anatomical structures along the selected line. To evaluate diaphragmatic thickness,, the probe is placed in the zone of apposition of the diaphragm to the rib cage, between the 8th and the 10th intercostals space in the mid-axillary line, 0,5-2 cm below the costophrenic sinus. In this area, the diaphragm is observed as a structure made of three distinct layers: the nearest line is the parietal pleura, the deeper one is the peritoneum; the diaphragm is the less echogenic structure between these two lines. The Thickening Fraction (TF) can be calculated as widely described in the literature.