Why Use Anything But a Standard Spontaneous Breathing Trial to Determine Readiness for Ventilator Discontinuation?

In recent years, there has been an increased emphasis on the need for daily spontaneous breathing trial (SBT) assessment and performance of SBTs where indicated.1 The implementation of the ABCDE bundle (awakening, spontaneous breathing trial, coordinated efforts between health professionals, standardized delirium assessment, early mobilization) to improve liberation from the ventilator has prompted us to refocus our attention on the importance of daily assessment of the need for sedation and the early initiation of SBTs in every mechanically ventilated patient. Based on current recommendations, the ideal approach to perform an SBT is to allow spontaneous unsupported breathing for 30 min to 2 h.2,3 This can be accomplished via the mechanical ventilator (zero PEEP and zero pressure support) or via a standard T-piece. Brochard et al4 demonstrated that in a selected population of patients, those having first failed an SBT, weaning was faster with pressure support ventilation (PSV), although subsequent trials have shown that the performance of an SBT, with or without PSV, results in the same outcome.5 In this issue of RESPIRATORY CARE, Teixeira et al6 conducted a randomized comparison of approaches to an SBT. They compared the efficacy of PSV to a T-tube and to the use of proportional assist ventilation (PAV) during the SBT in a heterogeneous population of 160 critically ill subjects with respiratory failure from several etiologies requiring ventilatory support for 24 h. Although their protocol was sound, their results showed no clinically relevant differences between groups. They found that length of mechanical ventilation, length of hospitalization, extubation failure, time to re-intubation, and need for tracheostomy were similar among groups. Essentially, it did not matter which approach was used to assess for extubation readiness. The results of this study are exactly what we expected! As indicated above, when all patient types are compared, the use of PSV during an SBT results in the same outcome as a T-piece.7 In addition, the authors indicate that there have been 3 previous comparisons of PAV with PSV during SBTs, all with negative results.8-10 Most importantly, the patient population they chose to study was one that generally can be rapidly discontinued from ventilatory support once weaning criteria are met. About 50% of the subjects randomized were trauma victims, 20% were subjects from the medical ICU, 23% had a history of COPD, and only 20% had a body mass index of 30%. The overall ICU mortality of the group was 3.7%, and hospital mortality was 10%. The bottom line is that the study population was one in which no one would expect any intervention affecting the way an SBT was conducted to have an effect on the process of ventilator discontinuation or on mortality.