Diaphragmatic Speckle Tracking During Spontaneous Breathing Trial

Currently, measurement of transdiaphragmatic pressure (Pdi) using oesophageal and gastric balloons is the gold standard for the assessment of diaphragmatic effort. This technique is relatively invasive and its interpretation may be complex. The diaphragmatic longitudinal strain (LSdi) and strain rate (LSRdi) might provide additional information in the assessment of diaphragmatic effort and movement during SBT, allowing early detection of diaphragmatic dysfunction. Patients will be monitored during a 30-120 minutes SBT consisting of no assistance on the ventilator using CPAP with a pressure level of 0 cmH2O. Parameters to evaluate diaphragm function will include diaphragmatic strain (LSdi and LSRdi), diaphragmatic thickening fraction (TFdi), and airway occlusion pressure (ΔP0.1 and ΔPocc). These parameters will be measured immediately before ('baseline') the SBT, as well as 2 minutes ('early' assessment), 15 ('intermediate' assessment) and 30 minutes ('late' assessment) after the beginning of the SBT.