Validation of rapid shallow breathing index displayed by the ventilator compared to the standard technique in patients with readiness for weaning

BACKGROUND: Rapid shallow breathing index (RSBI) is the most commonly used parameter for predicting weaning outcome. Measurement of RSBI by Wright spirometer (RSBI(standard)) is the standard method in routine clinical practice. Data specific to the accuracy and reliability of the RSBI value displayed by the ventilator (RSBI(vent)) are scarce. Accordingly, this study aimed to evaluate the association between the average value of RSBI(vent) at different time points and RSBI(standard), 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) (RSBI(standard)), and (2) the values displayed on the ventilator at 0, 15, 30, 45, and 60 s (RSBI(vent)). RESULTS: Forty-seven patients were enrolled. The RSBI(vent) value was significantly higher than the RSBI(standard) 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 RSBI(standard) and the RSBI(vent) 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 RSBI(vent) value among 5 time points (0, 15, 30, 45, and 60 s) was found to best correlate with RSBI(standard).