Chapter 58. Weaning from Mechanical Ventilation

Thirty years ago, the weaning of patients from the ventilator was relegated to nurses and respiratory therapists. It aroused little interest among physicians. It certainly wasn’t thought worthy of serious scientific inquiry. All this has changed. No other area of critical care has undergone so great a transformation. But the illumination has also cast shadows. In particular, discussion of weaning is now bedeviled by imprecise language. This can be seen as just deserts insofar as few clinicians use the term weaning in the strict literal sense—a gradual reduction in the level of ventilator support. Instead, most patients today are taken off the ventilator cold turkey. It would be fine if the confused language stopped there. But this is only one small example of how fundamental scientific misunderstanding has arisen from imprecise word choices.

Under the cloak of imprecise language, much muddled thinking, flawed logic, and misinterpretation has crept into the field. These language problems are not just pedantic quirks. Instead, they impede the rigor of research in this area, as well as interpretation of the findings. Communication is also hindered by the lumping together of many distinct components of this complex process. To enhance clarity, we divide weaning into seven stages.

We divide weaning into seven stages to draw attention to areas that receive minimal attention (Fig. 58-1). Stage 1 is preweaning, when no attempt at weaning is desirable. For example, when a patient is receiving 80% oxygen and positive end-expiratory pressure (PEEP) of 15 cm H2O, performing any disconnect from the ventilator (for measurement of weaning predictors) is inappropriate and may even be dangerous. Every ventilated patient begins at stage 1, and some patients never get beyond that stage. For example, in a prospective study of 249 ventilated patients,1 sixty-five patients (26%) died during mechanical ventilation without any attempt at weaning. In another report of 357 patients entered into a trial of weaning techniques,2 12.9% never reached the stage of any active weaning attempt. We identify this preweaning stage to emphasize the importance of the transition between it and the next stage of a patient’s clinical course.

Stage 2 is the period during which the clinician contemplates ...