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biofeedback may be helpful in decreasing the weaning time in patients who are having difficulty withdrawing from ventilatory support.97–98 EVIDENCE-BASED GUIDELINES FOR WEANING AND DISCONTINUING VENTILATORY SUPPORT 72 RESPIRATORY CARE • JANUARY 2002 VOL 47 NO 1 Criteria to Assess Ventilator Dependence Introduction The process of discontinuing mechanical ventilatory support begins with a recognition of adequate recovery from acute respiratory failure. Thereafter, careful clinical assessments are required to determine the patient’s readiness for subsequent discontinuation of ventilatory support and, ultimately, extubation. To facilitate this process, investigators have focused on identifying objective criteria to determine the answers to the following questions: When can efforts to discontinue ventilation be initiated? What assessment strategies will best identify the patient who is ready for ventilator discontinuation? When should extubation be carried out, and how can extubation outcome best be predicted? Evidence to answer these questions comes largely from observational studies in which a certain parameter (or set of parameters) is compared in a group of patients who either successfully or unsuccessfully have been removed from the ventilator. The general goal of these studies is to find “predictors” of outcome. Evaluating the results from these types of studies can be difficult for several reasons. First, the “aggressiveness” of the clinician/investigator’s weaning and discontinuation philosophy needs to be understood, as it will affect the performance of a given predictor. A very aggressive clinical philosophy will maximize the number of patients withdrawn from ventilatory support but could also result in a number of premature discontinuations, with a subsequent need for reintubations and/or reinstitution of support. In contrast, a less aggressive clinical philosophy will minimize premature discontinuations but could also unnecessarily prolong ventilatory support in other patients. Unfortunately, there are no good data to help clinicians to determine the best balance between premature and delayed discontinuations in evaluating a given discontinuation strategy. Clearly, extubation failure should be avoided whenever possible because the need for reintubation carries an 8-fold higher odds ratio for nosocomial pneumonia99 and a 6-fold to 12-fold increased mortality risk.100–103 In contrast, the maintenance of unnecessary ventilator support carries its own burden of patient risk for infection and other complications.104,105 Reported reintubation rates range from 4% to 23% for different intensive care unit (ICU) populations,100,101,103,104,106–110 and may be as high as 33% in patients with mental status changes and neurological impairment.103 Although the optimal rate of reintubation is not known, it would seem likely to rest between 5% and 15%. Second, a number of methodological problems exist with most of these observational studies. For instance, patients are recruited into these studies because investigators believe that there is some reasonable chance of success for ventilator discontinuation. These “entry” criteria often include some form of clinical judgment or intuition, making results from one study difficult to compare to another. In addition, clinician/investigators deciding to proceed with ventilator discontinuation/extubation often have not been blinded to the parameters being analyzed as possible predictors. Indeed, the parameter being analyzed may often enter into the clinical decision on whether either to continue or to discontinue ventilatory support. Other methodological problems with these observational studies include different measurement techniques of a given parameter from study to study, large coefficients of variation with repeated measurements or from study to study of a given parameter,111,112 different patient populations (eg, longterm vs short-term ventilator dependence),113,114 and the absence of objective criteria to determine a patient’s tolerance for a trial of either discontinuation or extubation. Third, assessed outcomes differ from study to study. Some investigators have examined successful tolerance of