Weaning from mechanical ventilation

Weaning from mechanical ventilation is a period of transition from total ventilatory support to spontaneous breathing. It represents a relevant clinical problem because as many as 25% of intubated and mechanically-ventilated critically ill patients will need a progressive withdrawal from artificial ventilatory support. From a clinical standpoint, it is very important to recognize as soon as possible when a patient is ready to be weaned. Accordingly, a daily routine follow-up should be performed in every patient in order to verify whether patients meet clinical criteria to be disconnected from the ventilator. Several physiological indices have been used to predict the outcome of weaning trials. However, an adequate clinical tolerance to spontaneous breathing during a 2 h T-piece trial is very useful to predict a successful extubation. A number of physiopathological mechanisms explain why some patients fail the weaning trials; particularly important from a clinical point of view are those related to respiratory pump failure and cardiovascular instability, which are usually accompanied by an abnormal gas exchange. Different ventilatory techniques can be used to wean these patients from mechanical ventilation. Up to now, the most efficient techniques seem to be pressure support ventilation and once daily trials of T-piece interspersed with conventional volume assist-control ventilation. Finally, knowledge-based system applied to modern microprocessor mechanical ventilators can help in the process of weaning by automatically reducing the ventilatory assistance and indicating the optimal time to perform extubation.