A method of extubation from mechanical ventilation best validated in the literature is one of a spontaneous breathing trial (SBT). A few randomized control trials comparing 30 versus 120 minute SBT’s found no difference in outcomes but the numbers of patients evaluated were small. In our ICU, we use a 90-minute CPAP trial to assess the patient’s likelihood of being extubated. Along with clinical parameters we use a rapid shallow breathing index (RSBI) as a quantifiable, objective measure of a patient’s tolerance of the SBT. Our objective is to evaluate whether RSBI changes significantly (20 point increase from baseline and crosses 100) from the beginning to the end of a 90-minute SBT.
We evaluated 164 consecutive medical ICU patients on mechanical ventilation at an urban teaching hospital. Of these, 141 were successfully extubated. Sixteen were extubated to non-invasive ventilation and 7 patients underwent tracheostomies. We excluded terminally extubated patients. A critical care fellow made decisions to extubate based on clinical information, negative inspiratory force, arterial blood gas, and RSBI. RSBI was calculated at 1, 30, 60, and 90 minutes of the SBT.
The mean RSBI’s for successfully extubated patients were 65, 63, 64, and 65 at 1, 30, 60, and 90 minutes, respectively. The mean RSBI’s for patients who failed extubation were 101, 80, 81, and 82 at 1, 30, 60, and 90 minutes, respectively. Of the successfully extubated patients, only 4 (2.8%) had a significant change in RSBI. Of the 23 who failed extubation five tolerated less than five minutes of the SBT. Of the remaining 18 patients, only 1 (5.6%) had a significant change in RSBI during the SBT. The patients who failed extubation despite meeting our screening criteria did so because of hypoxia, altered mental status, hypercarbia, or hypotension.
The RSBI does not change significantly during a 90 minute SBT.
Based on our results, we conclude that there is little to be gained by extending the SBT beyond the first 30 minutes.
N.G. Shah, None.