Evaluation of a 2-hour Educational Programme in Diaphragm Ultrasonographic Assessment

1. INTRODUCTION Diaphragm ultrasound non-invasively explores the diaphragm function and it can be useful in several clinical situations. Diaphragm ultrasound is able to evaluate the cranio-caudal displacement of the diaphragm and its thickening fraction at the end of inspiration, in relation to the end-expiratory value. These parameters provide useful data in the evaluation and management of patients affected by diaphragm dysfunction; moreover, they are gaining an increasing role in the evaluation of patients undergoing mechanical ventilation.

To assess the diaphragm activity, clinicians use two different sonographic windows:

i. to evaluate diaphragmatic thickness in the zone of apposition of the diaphragm to the rib cage. Physicians can assess thickening fraction between the 8th and 10th intercostal space, on the anterior or midaxillary line, 0.5-2 cm below the costophfrenic angle. The zone of apposition is the area of the chest wall where the abdominal contents reach the lower rib cage. In this area, the diaphragm is observed as a structure made of three distinct layers: a non-echogenic central layer bordered by two echogenic layers, the peritoneum and the diaphragmatic pleurae. To obtain adequate images of diaphragmatic thickness in M mode and 2D mode, a linear high-frequency probe (≥10 MHz) is necessary. The diaphragmatic thickness can be measured during quiet spontaneous breathing and during a maximal inspiratory and expiratory effort. An index of diaphragmatic thickening, the thickening fraction (TF) can be calculated using the M mode (TF = thickness at endinspiration - thickness at end-expiration/thickness at end-expiration). Diaphragmatic thickening fraction can be used as an index of diaphragmatic efficiency as a pressure generator. In normal individuals, there is a wide range of tdi at functional residual capacity (FRC), ranging between 1.8 to 3 mm. As lung volume increases from the residual volume (RV) to total lung capacity (TLC) there is a mean tdi increase of 54 % (range 42-78 %). Furthermore, the diaphragm also thickens during a maximal inspiratory pressure (Pimax) maneuver at FRC. A thickening ratio of 2.6 can be measured, dividing the diaphragmatic thickness during Pimax at FRC by the diaphragmatic thickness while relaxing at FRC.

ii. the physicians can also assess the diaphragmatic displacement (or excursion) trough a 3.5-5 mHz phased array probe. The probe is placed immediately below the right costal margin in the mid-clavicular line or in the right anterior axillary line, and it is directed medially, cephalad and dorsally, in order that the ultrasound beam perpendicularly reached the hemi-diaphragm in its posterior third portion. After obtaining the best approach in two-dimensional mode, the displacement was measured in M-mode displaying the motion of the hemi-diaphragm along the selected line. In healthy subjects during spontaneous breathing, the inspiratory diaphragm excursion is 1.34 ± 0.18 cm.

In patients undergoing assist mechanical ventilation, the thickening fraction is an indicator of inspiratory effort. While several studies have been conducted in the evaluation of educational programmes for echocardiography, to date data regarding this aspect in diaphragm ultrasonographic assessment lack. 2. AIM OF THE STUDY