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question. The one large randomized trial107 that compared routine SBTs to 2 other weaning strategies that did not include SBTs provides compelling evidence that SBTs administered at least once daily shorten the discontinuation period compared to strategies that do not include daily SBTs. In addition, 2 studies108,119 showing the success of protocol-driven ventilator discontinuation strategies over “usual care” both included daily SBTs. The subsequent use of routine subsequent SBTs in this patient population thus seems appropriate. EVIDENCE-BASED GUIDELINES FOR WEANING AND DISCONTINUING VENTILATORY SUPPORT RESPIRATORY CARE • JANUARY 2002 VOL 47 NO 1 77 There are several lines of evidence that support waiting 24 hours before attempting an SBT again in these patients. First, except in patients recovering from anesthesia, muscle relaxants, and sedatives, respiratory system abnormalities rarely recover over a short period of hours and thus frequent SBTs over a day may not be expected to be helpful. Supporting this are data from Jubran and Tobin52 showing that failed SBTs often are due to persistent respiratory system mechanical abnormalities that are unlikely to reverse rapidly. Second, there are data suggesting that a failed SBT may result in some degree of respiratory muscle fatigue.50,117,118 If so, studies126,140 conducted in healthy subjects suggest that recovery may not be complete for anywhere from several hours to 24 hours. Third, the trial by Esteban et al107 specifically addressed this issue and provided strong evidence that twice-daily SBTs offer no advantage over a single SBT and, thus, would serve only to consume unnecessary clinical resources. Recommendation 6. Patients receiving mechanical ventilation for respiratory failure who fail an SBT should receive a stable, nonfatiguing, comfortable form of ventilatory support. Rationale and Evidence (Grade B) There are a number of ventilator modes that can provide substantial ventilatory support as well as the means to reduce partial ventilatory support in patients who have failed an SBT (Table 7). A key question, however, is whether attempts at gradually lowering the level of support (weaning) offer advantages over a more stable, unchanging level of support between SBTs. The arguments for using gradual reductions are (1) that muscle conditioning might occur if ventilatory loads are placed on the patient’s muscles and (2) that the transition to extubation or to an SBT might be easier from a low level of support than from a high level of support. Data supporting either of these claims, however, are few. However, maintaining a stable level of support between SBTs reduces the risk of precipitating ventilatory muscle overload from overly aggressive support reduction. It also offers a substantial resource consumption advantage in that it requires far less practitioner time. The study by Esteban et al107 partially addressed this issue in that it compared daily SBTs (and a stable level of support in those who failed) to 2 other approaches using gradual reductions in support (ie, weaning with pressure support or intermittent mandatory ventilation [IMV]) and demonstrated that the daily SBT with stable support between tests permitted the most rapid discontinuation. What has not been addressed, however, is whether gradual support reductions coupled with daily SBTs offer any advantages. The McMaster AHCPR report4 identified 3 other randomized trials109,141,142 that compared gradual reduction strategies using different modes but not routine daily SBTs. The study by Brochard et al109 was the most similar in design to the study by Esteban et al107 that was noted before, and it included a pressure-support group and an IMV group. A third group received gradually increasing fixed periods of spontaneous breathing that were designed only to provide brief periods of work and not specifically to test for discontinuation (ie, they were not routine daily SBTs, as defined above). The results showed that their use of gradually lengthening spontaneous breathing periods was inferior to other strategies and, like the Esteban trial, the pressure support strategy was easier to reduce than the IMV strategy. The other 2 randomized trials141,142 that were identified by