What is the optimal approach to weaning and liberation from mechanical ventilation?

"Weaning" refers to the transition from full mechanical ventilatory support to spontaneous ventilation with minimal support. “Liberation” refers to discontinuation of mechanical ventilation.1 This chapter focuses on the clinical assessment of readiness to wean, the technique for conducting a spontaneous breathing trial (SBT), and the assessment of readiness of extubation. In addition, we will review the evidence supporting various ventilator strategies in the difficult-to-wean patient. Mechanically ventilated intensive care patients may be classified as simple to wean, difficult to wean, or prolonged weaning.2,3 Simple-to-wean patients are extubated on the first attempt, make up the vast majority of the patients in the intensive care unit (ICU; ∼69%), and have a low mortality rate (∼5%).4,5 The remaining cohort of difficult-towean (requiring up to three attempts or up to 7 days from the onset of weaning) or prolonged-wean (over three attempts or greater than 7 days from the onset of weaning) patients require greater effort to successfully liberate from mechanical ventilation. These difficult-to-wean and prolonged-wean patients have an associated higher mortality rate (∼25%).4,5 Prolonged mechanical ventilation is associated with increased mortality6 and costs (mechanical ventilation costs > U.S. $2000/day).7 It has been estimated that the 6% of patients who require prolonged mechanical ventilation consume 37% of ICU resources,8 and 40% to 50% of the time spent undergoing mechanical ventilation occurs after this weaning process has started.4,6,9 In part, the reason is that more severely ill patients usually require longer periods of mechanical ventilation. Prolonged weaning may result, though, from an excessive use of sedatives, the absence of weaning-liberation protocols, and myriad of organizational and cultural factors that fail to optimize weaning conditions. In general, the duration of mechanical ventilation should be minimized, and liberation from mechanical ventilation should be considered as soon as possible. Expert consensus2 has proposed that the weaning process be considered in the following six steps: 1. Treatment of acute respiratory failure 2. Clinical judgment that weaning may be possible 3. Assessment of the readiness to wean 4. An SBT 5. Extubation 6. Possibly re-intubation Depending on the mechanism of acute respiratory failure—whether it is a problem of oxygenation, ventilation, or airway (or a combination)—most critically ill patients require a period in which they will require full ventilatory support after intubation. Consideration of the weaning process should begin very soon after intubation. Weaning involves several discrete logical and sequential steps. If patients fail to make sufficient progress, then a contingency plan is required. Failure to wean/liberate involves either (1) the failure of an SBT or (2) the need for re-intubation/ ventilation or death within 48 hours of extubation.2