ABSTRACT
BACKGROUND: Rapid shallow breathing index (RSBI) is the most commonly used parameter for predicting weaning outcome. Measurement of RSBI by Wright spirometer (RSBIstandard) is the standard method in routine clinical practice. Data specific to the accuracy and reliability of the RSBI value displayed by the ventilator (RSBIvent) are scarce. Accordingly, this study aimed to evaluate the association between the average value of RSBIvent at different time points and RSBIstandard, and to assess the accuracy and reliability of these two RSBI measurement techniques. METHODS: This prospective cohort study included mechanically ventilated patients who were ready to wean. At the beginning of spontaneous breathing trial using the flow-by method, RSBI was measured by two different techniques at the same time, including: (1) Wright spirometer (breathing frequency/average tidal volume in 1 min) (RSBIstandard), and (2) the values displayed on the ventilator at 0, 15, 30, 45, and 60 s (RSBIvent). RESULTS: Forty-seven patients were enrolled. The RSBIvent value was significantly higher than the RSBIstandard value for every comparison. According to Spearman's correlation coefficient (r) and intraclass correlation coefficient (ICC), the average value of RSBI from 5 time points (0, 15, 30, 45, and 60 s) showed the best correlation with the standard technique (r = 0.76 [P < 0.001], and ICC = 0.79 [95% CI 0.61-0.88], respectively). Bland-Altman plot also showed the best agreement between RSBIstandard and the RSBIvent value averaged among 5 time points (mean difference - 17.1 breaths/min/L). CONCLUSIONS: We found that the ventilator significantly overestimates the RSBI value compared to the standard technique by Wright spirometer. The average RSBIvent value among 5 time points (0, 15, 30, 45, and 60 s) was found to best correlate with RSBIstandard.
