Objectives:

Because mechanical ventilation incurs significant morbidity, mortality, and costs and because premature extubation as well as delayed extubation can cause harm, weaning that is both expeditious and safe is highly desirable. We sought to determine whether the current literature elucidates when and how weaning should begin, proceed, and end.

Search Strategy:

We used five computerized bibliographic databases, hand searching, bibliographic references, expert consultation, and a duplicate independent review process to identify relevant articles.

Selection Criteria:

Our eligibility criteria were broad. We selected studies evaluating any weaning modes, algorithms, or other interventions to facilitate weaning; studies of weaning predictors; and studies evaluating patient and nursing experiences during weaning.

Data Collection and Analysis:

We developed generic forms to abstract data from all studies, in addition to forms specific to randomized trials, nonrandomized controlled studies, and studies of weaning predictors. We developed an instruction manual and trained eight individuals to abstract data related to study characteristics and results using duplicate, independent review. Quantitative data were abstracted using several metrics. We pooled results across randomized trials and across studies of weaning predictors only when our assessment of the patients, interventions, and outcomes indicated that pooling was legitimate.

Main Results:

We reviewed 154 articles. For stepwise reductions in mechanical support, pressure support mode or multiple daily T-piece trials may be superior to synchronized intermittent mandatory ventilation. For trials of unassisted breathing, low levels of pressure support may be beneficial. There may be substantial benefits to early extubation and institution of noninvasive positive pressure ventilation before patients are ready to breathe without mechanical assistance. The value of differing modes as reflected in these studies depends on the thresholds for initiating, progressing through, and terminating weans in the specific study protocols. Unfortunately, these thresholds involve more than objective data and appear to be related to physician judgment.

The implementation of nurse-driven or respiratory therapist-driven weaning protocols, regardless of what modes are employed, significantly expedites weaning and is probably safe. Following cardiac surgery, early extubation is unequivocably achieved with a variety of anesthetic interventions and intensive care unit protocols; however, the corresponding reduction in intensive care unit stay is generally small and the impact on complications, though rare, remains unclear. The role of computerized protocols has not been established.

We did not uncover any consistently powerful weaning predictors. The most frequently studied and one of the most helpful tests is the rapid shallow breathing index; however, the pooled likelihood ratio for a positive test ranged from 1.3 to 2.8. Two other predictors, occlusion pressure/maximum inspiratory pressure and the compliance, rate, oxygenation, and pressure index, are more powerful, though less intensively studied. In general, the probable reason for the poor performance of weaning predictors is that physicians have already considered the results of these predictors when they select patients for study.

Conclusions:

Future research initiatives should include: determining the optimal tradeoff between prolonged time on a ventilator and reintubation in specific patient groups, further evaluation of weaning protocols (What types of patients are most likely to benefit? Which protocols are most effective? How large are the associated cost reductions? Is there a role for computers?), and clarification of the risk-benefit of early extubation with noninvasive positive pressure ventilation.