Timing and Criteria for Beginning Weaning
Mechanical ventilation (MV) is a supportive tool for critically ill patients which saves lives worldwide each day. Nevertheless, this advantage is obtained at the cost of additional morbidity and mortality. The classical side effects of MV are widely reco
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Mechanical ventilation (MV) is a supportive tool for critically ill patients which saves lives worldwide each day. Nevertheless, this advantage is obtained at the cost of additional morbidity and mortality. The classical side effects of MV are widely recognized in the form of tracheal damage, need for sedatives, and hemodynamic disturbances. In the 1980s, the impact of pulmonary infections, so-called ventilator-associated pneumonia, was the target of substantial research in the field of adverse consequences of MV. In the 1990s, the focus was directed to the direct damage caused by MV on the lungs, and such terms as "barotrauma", "volotrauma", and recently "biotrauma" were tailored to define different problems directly related to the use of life-saving MV. The recognition of such iatrogenic problems fueled the research in methods to reduce their intensity (e.g. reducing airway pressure, reducing tidal volumes), but also to reduce the time of exposure to these agents by reducing the length of MY. In a frequently cited study, Esteban et al. [1] showed that a large proportion of the time spent under MV was dedicated to weaning. At that time, in 1992, as much as 40% of the time under MV was related to weaning. In a more recent report [2], the same investigator chaired a I-day prevalence study of 412 ICDs from North America, South America, Spain, and Portugal. The study involved 1638 ventilated patients, 520 (32%) of whom were being weaned at that moment. This means that a high proportion of the workload dedicated to MV patients is devoted to weaning, and that the most common approach to weaning is still a progressive reduction of ventilatory support. Nevertheless, in the past decade we have learned that the majority of patients do not need such a progressive withdrawal of MV [3]. In these patients, prolonging MV will be of no benefit, while the deleterious effects of MV appeared as unacceptable from a risk/benefit ratio. At this point, we can summarize the field of decisions about weaning in terms of "when to start weaning" and "how to proceed with weaning". In both issues, we can suggest two opposite approaches, i.e. the more "conservative" method and the more "aggressive" method. In the "conservative" approach to starting weaning a physician waits for physiological parameters to return to "normal" values before attempting to evaluate whether the patient is able to resume spontaneous ventilation, in other words, for the patient to «fully" recover from the initial condition requiring MY. In this scenario, wide variability exists regarding the minimal values that a patient "must" exhibit before weaning can be started. In contrast, the "aggressive" approach to starting weaning will consider a patient able to be J. Mancebo et al. (eds.), Mechanical Ventilation and Weaning © Springer-Verlag Berlin Heidelberg 2003
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weaned as early as possible, i.e. when he or she does not show signs of life-threatening worsening after MV is stopped. Again, what can be described as "clinically significant" worsening remain
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