A comparison of the rapid shallow breathing index and complexity measures during spontaneous breathing trials after cardiac surgery

PurposeExtubation failure is associated with worse outcomes. Physicians use respiratory parameters to help them to decide to extubate or not. The purpose of this study is to determine if novel measures of respiratory physiology such as complexity and variability can identify patients who will tolerate extubation.MethodsEighty-three patients who required reinstitution of mechanical ventilation after extubation (Extub-Fail) were matched to 83 patients who successfully tolerated extubation (Extub-Success) and to 83 who failed a spontaneous breathing trial (SBT-Fail). Patients were compared using interbreath intervals and tidal volumes using means, SDs, measures of complexity, spikiness, and rapid shallow breathing index (RSBI).ResultsFrom SBT-Fail to Extub-Fail to Extub-Success, the interbreath intervals progressively lengthened (mean ± SD, 2.2 seconds ± 0.6 vs 2.5 ± 0.6 vs 2.7 ± 0.8; P < .001), became more variable (mean ± SD, 0.57 ± 0.13 vs 0.62 ± 0.21 vs 0.66 ± 0.23; P = .012), and became more complex. Complexity as measured by approximate and sample entropy was greater in the Extub-Success group than in the SBT-Fail group. Patients who were in the SBT-Fail group had a higher RSBI than did either of the extubated groups, but there was no difference in RSBI between Extub-Success and Extub-Fail.ConclusionsPatients who successfully tolerate extubation have longer interbreath interval with greater complexity and variability of that series. Although the VT was similar between the Extub-Success and the SBT-Fail groups, the Extub-Success group had greater long-term complexity with no difference in short-term complexity. This implies that the respiratory controllers are differently impacted in patients tolerating or not tolerating extubation.