Comparison of different methods of obtaining the rapid shallow breathing index.

OBJECTIVE: To compare the Rapid Shallow Breathing Index (RSBI) obtained by the ventilometer and from mechanical ventilation parameters. METHODS: Randomized crossover trial, including 33 intubated patients, on mechanical ventilation for at least 24 hours, undergoing spontaneous breathing test. Patients were submitted to the measurement of RSBI by four methods: disconnected from the ventilator through the ventilometer; in Pressure Support Ventilation (PSV) mode at a pressure of 7.ßcm H2O; in Continuous Positive Airway Pressure (CPAP) mode at a pressure of 5.ßcmH2O with flow trigger; in CPAP mode at a pressure of 5.ßcmH2O with pressure trigger. RESULTS: No significant difference was detected between the RSBI obtained by the ventilometer and in the CPAP mode with flow and pressure triggers, however, in the PSV mode, the values were lower than in the other measurements (p.ß<.ß0.001). By selecting patients from the sample with higher RSBI (... 80 cycles.min-1.L-1), the value of the index obtained by the ventilometer was higher than that obtained in the three options of ventilation methods. CONCLUSION: The RSBI obtained in the CPAP mode at a pressure of 5.ßcmH2O, in both triggers types, did not differ from that measured by the ventilometer; it is, therefore, an alternative when obtaining it from mechanical ventilation parameters is necessary. However, in the presence of borderline values, the RSBI measured by ventilometer is recommended, as in this method the values are significantly higher than in the three ventilation modalities investigated.