Diaphragmatic Tissue Doppler During Weaning From Mechanical Ventilation

Tobin Index (RSBI), which is the ratio between respiratory rate (RR) and tidal volume (VT), is one of the most used indices to predict weaning outcome. The diaphragm plays a key role in generating VT and, in the case of diaphragmatic dysfunction, inspiratory accessory muscles may contribute to support ventilation. If this occurs during a spontaneous breathing trial (SBT), it will probably result in delayed weaning, since the accessory muscles are more fatigable than the diaphragm. The diaphragmatic tissue Doppler imaging (TDI) is an ultrasonographic technique derived from ultrasound evaluation of heart's motility. Being a muscle doppler assessment, it can be easily used on the diaphragm to calculate the speed of muscles displacement that could be associated with patient's respiratory drive, as well as other derived index of muscle function. The aim of the study is to measure the variations of diaphragmatic displacement velocities before and during the spontaneous breathing trial, useful to check if the patient is ready to breathe spontaneously. An observational study will be performed. Patients who are ready to be weaned will be subjected to a spontaneous breathing test (Cpap 5), that consists of applying a positive end-expiratory pressure of 5 cm H2O for 20 minutes. A tissue Doppler evaluation will then be performed by analyzing the diaphragmatic displacement velocity during inspiration and expiration in the modality of ventilation which precedes the trial and during the SBT. Vital parameters will be monitored during the study. Mechanical ventilation length, incidence of tracheostomies, ICU and hospital recovery duration and hospital mortality will also be acquired.