Comparing Ventilator-displayed Rapid Shallow Breathing Index Values Versus Standard Measurement Techniques: A Bench Study

Background: The rapid shallow breathing index (RSBI) is a key indicator for assessing weaning readiness, based on simple and non-invasive measurements. However, the standard method requires patient cooperation, specialized equipment, and patient disconnection from the ventilator, which increases the risk of aerosol dispersion. Many modern ventilators address these limitations by displaying RSBI values directly on the screen; however, the accuracy and reliability of the displayed data have yet to be confirmed. This study compared the accuracy of RSBI values obtained from ventilators with the gold standard method using a lung simulator. Methods: This bench study was conducted using a manikin equipped with a lung simulator designed to mimic spontaneous breathing under preset resistance and compliance (normal, obstructive, restrictive) conditions. Two ventilators were tested under three modes: continuous positive airway pressure (CPAP) at 0 and 5 cmH ₂ O, and pressure support ventilation (PSV) at 5 cmH ₂ O combined with positive end-expiratory pressure (PEEP) of 5 cmH ₂ O. RSBI values displayed by the ventilators were recorded at 0, 15, 30, 45, and 60 seconds. The standard handheld method required disconnection of the ventilator to measure the minute volume (MV), from which tidal Volume (V _T ) and RSBI were calculated. Results: In PSV mode, the average RSBI value was significantly lower than that measured using the spirometer; however, no difference was detected in CPAP mode. No significant differences in mean RSBI values were detected across different flow trigger settings, irrespective of the operating mode. The choice of flow trigger was not correlated with airway pressure, RSBI, MV, V _T , respiratory rate, PSV level, or PEEP. Bland-Altman plots revealed good agreement between ventilator-measured RSBI values and those obtained using a handheld spirometer RSBI in CPAP mode. Conclusions: RSBI values presented by the ventilator in PSV mode were significantly lower than those obtained using a handheld device. No discrepancies were observed in CPAP mode, and flow trigger settings did not have a significant effect on RSBI measurements. Clinicians should be cautious of the deviation in RSBI values captured in PSV mode. Our findings suggest that CPAP mode may be a more suitable option for assessing weaning readiness.