Weaning Patients from the Ventilator

Several studies suggest that the process of discontinuing ventilation after the underlying cause of respiratory failure has been addressed accounts for more than half the total duration of mechanical ventilation.6,7 Minimizing the duration of mechanical ventilation is an important consideration for all clinicians who care for critically ill patients. The first textbook on mechanical ventilation, published in 1965, stated, “To know the proper timing and rate of weaning from the respirator requires considerable judgment and experience. As a rule, weaning should start as soon as possible.”8 There is support in the literature for this notion that quick discontinuation of mechanical ventilation is beneficial. In a prospective observational study involving patients with brain injuries, Coplin et al.9 compared discontinuation of mechanical ventilation within 48 hours after readiness criteria had been met with more than a 48-hour delay in discontinuation. There was higher mortality, an increased risk of pneumonia, and a longer hospital stay in the group with delayed discontinuation than in the group in which ventilation was discontinued in a more timely fashion. Thus, clinicians should be motivated to minimize the duration of mechanical ventilation. Table 1 outlines evidence-based treatment strategies to prevent the need for mechanical ventilation as well as interventions to reduce the duration of mechanical ventilation once it has been initiated. Several studies have investigated whether particular methods of ventilatory assistance were associated with earlier discontinuation of mechanical ventilation. Brochard et al.21 and Esteban et al.22 conducted studies that compared a gradual reduction of ventilatory support with spontaneousbreathing trials in patients in medical–surgical ICUs in whom initial spontaneous-breathing trials had been unsuccessful. Although these studies came to different conclusions about which method led to earlier discontinuation of mechanical ventilation, both suggested that subsequent trials of spontaneous breathing were successful in most patients — nearly 76%. These findings provide support for the notion that most patients with acute respiratory failure are quickly able to resume spontaneous respiration if their physicians afford them the opportunity to do so. Efforts to decrease the duration of mechanical ventilation can be divided into two categories: earlier appreciation of readiness for spontaneousbreathing trials and a shorter process of discontinuing mechanical ventilation. Many studies have tried to identify simple measurements that can help clinicians predict which patients are ready for a spontaneous-breathing trial and in which nejm. org Table 1. Strategies to Prevent the Need for Mechanical Ventilation and to Reduce Its Duration. Strategy Source Evidence-based approaches to reduce the need for mechanical ventilation Rivers et al.10 Early goal-directed therapy in the initial treatment of sepsis Use of noninvasive ventilation in selected patients with an acute exacerbation

• f chronic obstructive pulmonary disease or acute cardiogenic pulmonary edema

Brochard et al.,11 Ram et al.,12 Masip et al.,13 Gray et al.14 Ventilator management and associated care to reduce the duration of mechanical ventilation Use of small tidal volumes (6 ml/kg of ideal body weight) in patients with the acute respiratory distress syndrome The Acute Respiratory Distress Syndrome Network15 Daily interruption of sedative infusion Kress et al.16 Interruption of sedative infusion before spontaneous-breathing trial Girard et al.5 Schweickert et al.17 Early physical and occupational therapy Strøm et al.18 No use of sedatives in patients receiving mechanical ventilation Conservative strategy of fluid management in patients with acute lung injury ARDS Clinical Trials Network19 Strategies to reduce ventilator-associated pneumonia Dezfulian et al.20 patients these trials are most likely to be successful. Yang and Tobin23 found that a ratio of the respiratory rate (expressed in breaths per minute) to tidal volume (expressed in liters) (f: Vt) of 105 breaths per minute per liter or less during a 1-minute trial with the use of a T-piece was quite accurate in identifying patients in whom a subsequent spontaneous-breathing trial would be successful (positive predictive value, 78%; negative predictive value, 95%). However, most experts agree that the best method of determining whether patients are ready to breathe on their own is to perform a trial of spontaneous breathing once they have met readiness criteria.24 Many ICUs use protocols to guide the transition from assisted ventilation to spontaneous breathing and subsequent discontinuation of mechanical ventilation. Most protocols include three components: objective criteria to determine whether a patient is ready to breathe with reduced ventilatory support, structured guidelines for reducing ventilatory support, and a list of criteria to determine whether a patient is ready for extubation. There is also growing consensus that the use of systematic protocols for discontinuation of mechanical ventilation, as compared with usual care, may reduce the duration of mechanical ventilation.25 However, not all studies that use protocols for these strategies have shown improvement

• ver usual care.26-29 Because there are differences between readiness criteria for spontaneous-breathing trials and algorithms for discontinuation of mechanical ventilation, it is difficult to definitively state which aspect or aspects of these protocols are responsible for a reduction in the duration of mechanical ventilation. Nevertheless, the reproducible benefit shown in studies of various protocols in multiple ICUs suggests that it is the standardized approach to management rather than any specific method of ventilator support, prespecified readiness, or criteria for discontinuation of mechanical ventilation that reduces the duration of mechanical ventilation and improves outcomes. Thus, most guidelines recommend that patients who are receiving mechanical ventilation be assessed daily for their readiness to breathe spontaneously and afforded the opportunity to do so if they meet prespecified criteria.24

Trials of spontaneous breathing do not succeed for a variety of reasons.

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