Compare rapid shallow breathing index (RSBI) derived using different methods in the Medical ICU (MICU) and standardize RSBI measurement through the ventilator circuit.
We measured the RSBI in MICU patients viewed as ready for assessment of predictive extubation parameters. The respiratory rate (RR) and tidal volume (VT) were measured using three different methods: Method 1) CPAP and pressure support set at 0 cm of H2O with the FiO2 set at 0.4.Method 2) CPAP set at 5 and pressure support set at 0 cm of H20 with the FiO2 set at 0.4. Method 3) Patient disconnected from the ventilator with the Fi02 set at 0.21. VT and RR were recorded at the end of one minute from values displayed on the ventilator monitor in methods 1 and 2; and from a hand-held spirometer and the patient's observed RR in method 3. All three measurements were obtained sequentially in random order for each patient.
91 assessments, each one including values using methods 1–3, were obtained from 38 patients. Mean RSBI values for methods 1, 2 and 3 were 102±7.3, 88±6.2 and 114±8.1 respectively. The difference in the RSBI values using method 1 was significantly lower than that obtained using method 3102± 7.3 vs. 114±8.1) (p<0.0001). The RSBI decreased by 10.5% during method 1 and 22 % during method 2 as compared to method 1. The difference may be due to a minimal amount of pressure that the patient receives with the flow-by triggering while on CPAP.
RSBI values derived through the ventilator with settings of CPAP 0 cm of H20 are lower than values obtained using a handheld spirometer.
The RSBI can be conveniently measured through the ventilator circuitry; however a lower value may be more appropriate than the cut off value of 105 recommended by Yang and Tobin using Method 3.
Neeraj Desai, No Financial Disclosure Information; No Product/Research Disclosure Information