Mechanical ventilation (MV) is the major life-support modality during respiratory failure. Once the illness that precipitated respiratory failure has resolved, MV can be discontinued. <sup>75 Venous B., Smith R.A., Mathru M. National survey of methods and criteria used for weaning from mechanical ventilation Crit Care Med 1987 ;  15 : 530

Cliccare qui per andare alla sezione Riferimenti</sup> Practically, resolution of the lung injury that caused respiratory failure, and restoration of respiratory pump function may be slow, and are often incomplete at the time weaning is initiated. The risk of ventilator-associated complications, as well as the economic pressure of resource-intensive critical care, combine to favor the shortest duration of mechanical ventilation as can be safely achieved.

This goal should be served by weaning, the process and procedure of discontinuing MV. In the past, weaning has been specifically defined as the gradual withdrawal of ventilator support, <sup>69 Slutsky A.S. ACCP consensus conference: mechanical ventilation Chest 1993 ;  104 : 1833  [cross-ref]

Cliccare qui per andare alla sezione Riferimenti</sup> but two factors merit excluding chronology from its definition: (1) the ambiguity of what constitutes gradual withdrawal; and (2) the difficulty of assessing the time course of reloading patients' respiratory pump (i.e., when weaning is actually occurring) since modern weaning modes are equally capable of providing full ventilatory support. Patients who can tolerate abrupt discontinuation of MV are by definition not dependent on MV, and do not require weaning. It is preferable to define weaning in the context of ventilator-dependence, rather than by the slowness of withdrawal. As for the seemingly obvious end-point, breathing without mechanical ventilatory support, the patient is successfully weaned only when a pre-defined period of time passes without need for reinstitution of MV.