Pulmonary Rehabilitation in the Chronically Critically Ill Patient

The goal of this observational study is to learn about the population of chronically critical ill patients who refer to respiratory rehabilitation units. The main questions it aims to answer are: * what are the clinical and pathophysiological characteristics of the population of chronically critical ill patients who refer to respiratory rehabilitation units after hospital admission with the need for prolonged invasive mechanical ventilation via tracheostomy? * what is the response of this patient population to respiratory rehabilitation treatment in terms of functional recovery, weaning from invasive mechanical ventilation, weaning from tracheostomy tube, mortality and return to home? * are there any appreciable indices at admission and/or in the first period of hospitalization which may have a prognostic significance both on short-term objectives (weaning from invasive mechanical vent