The Science Journal of the American Association for Respiratory Care
Study Question: Can the Rapid Shallow Breathing Index (RSBI) be used as a reliable predictor of successful ventilator weaning and be incorporated into protocol in patients following cardiovascular surgery? This index is calculated by dividing the frequency (respiratory rate) by the tidal volume (VT) in liters. A value of <100 predicts successful weaning and a value of > 100 predicts failure to wean. The CO2SMOS+ Respiratory Profile Monitor (Novametrix Medical Systems, Wallingford, CT) Ventilation Monitor calculates RSBI as one of its parameters. Through a collaborative effort between Respiratory Care, Nursing, and CV Anesthesia, a ventilator weaning protocol has been the standard of care since 1988. The surgical groups included in the protocol are Coronary Artery Bypass (CAB), Aortic Valve Replacement (AVR), Mitral Valve Replacement (MVR) and Abdominal Aortic Aneurysm (AAA). All patients are protocol eligible unless they are on a balloon-pump, Left or Right Vascular Assistive Device (LVAD/RVAD). Decision making algorithms are used to ensure consistency of protocol implementation. The protocol has initial ventilator set-up parameters. Mechanical ventilatory interventions include SIMV, pressure support (PS) and CPAP. The 4 stage protocol includes assessment criteria and associated clinical interventions. The fourth stage utilizes traditional weaning mechanics to evaluate for extubation. Patients must have a Negative Inspiratory Force (NIF) of >25cmH20, VT 5-7 cc/kg, and a VC 12-15 cc/kg and normal arterial blood gases (ABG's). Method: RSBI was evaluated to determine if it could be used to replace or be an adjunct to traditional ventilation weaning predictors. An initial study group of 10 patients was selected to determine if further study was justified. The surgical procedure in the study group was Coronary Artery Bypass (CAB). The CO2SMOS+ was used to calculate RSBI. Clinical outcome evaluation was accomplished by successful weaning prediction utilizing RSBI and reintubation rates within 24 hours.
Results: Analysis demonstrated the following. All patients met the traditional weaning parameters. An RSBI average was 60.67 with a range of 11-117. The reintubation rate of 0% (Total population divided by reintubated population).
Conclusions: In cardiovascular patients the use of RSBI can indicate successful weaning without reintubation within 24 hours. The RSBI calculated by the CO2SMOS+ was clinically acceptable. Further investigation is warranted to determine if RSBI could replace or be an adjunct to traditional extubation predictors in the cardiovascular ventilation weaning protocol.