Although mechanical ventilation is a life-saving intervention, it is associated with a number of complications and has its own mortality (see Chapter 14). Because the risk of complications increases with the duration of mechanical ventilation, it is important not to prolong the duration of mechanical ventilation unnecessarily. The process of withdrawing mechanical ventilation is commonly referred to as ‘weaning’, but in the literature the term has acquired two distinct meanings, having been described as either (1) the process of gradually decreasing ventilatory support to return the work of breathing back to the patient or (2) a means of determining when patients have the ability to be safely liberated from the ventilator. Much of the available literature on weaning in fact refers to the second definition; furthermore, much of this work is difficult to interpret because successful extubation has been used as the end-point to assess ventilator independence. These are not synonymous because it is possible for a patient to be capable of self-ventilation without being ready for extubation. In this chapter, therefore, the term ‘weaning’ refers only to the process of returning the work of breathing back to the patient. Determining readiness for extubation or de-cannulation is dealt with as a separate issue.

The majority of patients admitted to a general ICU do not stay very long and their stays account for only a small proportion of the bed-days (Figure 18.1).