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combinations of subjective assessment and objective criteria (eg, usually gas exchange improvement, mental status improvement, neuromuscular function assessments, and radiographic signs) that may serve as surrogate markers of recovery have been employed (Table 3).101–103,107–109,119,120 It should be noted, however, that some patients who have not ever met one or more of these criteria still have been shown to be capable of eventual liberation from the ventilator.104 These “clinical assessments” of the status of the patient’s respiratory failure, however, are not enough to make decisions on the discontinuation of support. For example, one survey121 of intensivists using clinical judgment to assess the potential for discontinuation found a sensitivity of only 35% (6 of 17 patients who were successfully discontinued were identified) and a specificity of 79% (11 of 14 who failed discontinuation were identified). Moreover, in 2 large trials,107,109 despite the presence of apparent disease stability/reversal prior to performing a screening SBT, the managing clinicians did not recognize that discontinuation was feasible in almost two thirds of the subjects. Thus, the conclusion is that some evidence of “clinical” stability/reversal is a key first step in assessing for discontinuation potential but that more focused assessments are needed before deciding to continue or discontinue ventilatory support. Recommendation 3. Formal discontinuation assessments for patients receiving mechanical ventilation for respiratory failure should be done during spontaneous breathing rather than while the patient is still receiving substantial ventilatory support. An initial brief period of spontaneous breathing can be used to assess the capability of continuing onto a formal SBT. The criteria with which to assess patient tolerance during SBTs are the respiratory pattern, adequacy of gas exchange, hemodynamic stability, and subjective comfort. The tolerance of SBTs lasting 30 to Table 3. Criteria Used in Weaning/Discontinuation Studies to Determine Whether Patients Receiving High Levels of Ventilatory Support Can Be Considered for Discontinuation (ie, Entered Into the Trials)* Objective Measurements Adequate oxygenation (eg, PO2 60 mm Hg on FIO2 0.4; PEEP 5–10 cm H2O; PO2 /FIO2 150–300) Stable cardiovascular system (eg, HR 140 beats/min; stable blood pressure; no or minimal vasopressors) Afebrile (eg, temperature 38°C) No significant respiratory acidosis Adequate hemoglobin (eg, Hgb 8–10 g/dL) Adequate mentation (eg, arousable, GCS 13, no continuous sedative infusions Stable metabolic status (eg, acceptable electrolytes) Subjective Clinical Assessments Resolution of disease acute phase; physician believes discontinuation possible; adequate cough PO2 partial pressure of oxygen FIO2 fraction of inspired oxygen PEEP positive end-expiratory pressure HR heart rate GCS Glasgow Coma Scale *Adapted from References 101–103, 107–109, 119, and 120 EVIDENCE-BASED GUIDELINES FOR WEANING AND DISCONTINUING VENTILATORY SUPPORT 74 RESPIRATORY CARE • JANUARY 2002 VOL 47 NO 1 120 minutes should prompt consideration for permanent ventilator discontinuation. Rationale and Evidence (Grade A) Because clinical impression is so inaccurate in determining whether or not a patient meeting the criteria listed in Table 3 will successfully discontinue ventilatory support, a more focused assessment of discontinuation potential is necessary. These assessments can be performed either during spontaneous breathing or while the patient is still receiving substantial ventilatory support. These assessments can be used not only to drive decisions on weaning and discontinuation (ie, functioning as predictors) but also to offer insight into mechanisms of discontinuation failures. The McMaster AHCPR report4 found evidence in the literature supporting a possible role for 66 specific measurements as predictors. Some of these (eg, the negative effects of the duration of mechanical ventilation, and the length of/difficulty of surgery44,122–124) were derived from general clinical observations, but most were from studies on focused assessments of the patient’s