Since first proposed by Tobin et al the Rapid Shallow Breathing Index (RSBI) has become one of the most important parameters used to predict the likelihood of weaning from mechanical ventilation (MV). The purpose of this study was to see if the RSBI on pressure support ventilation (RSBI-PSV) was correlated with or was able to predict the RSBI on spontaneous breathing (RSBI-SB).
Prospective randomized trial comparing RSBI-PSV with RSBI-SB in patients receiving MV via endotracheal or tracheostomy tube considered ready to be weaned from MV. The order of RSBI-PSV versus RSBI-SB was randomized. Whichever technique was performed first, the other was performed 5 minutes later. RSBI-PSV used PSV 5 cm, PEEP 5 cm, and FiO2 21%. RR and TV were obtained from the ventilator. RSBI-SB was done on a T-piece on room air. Measurements were obtained using a Wright's handheld spirometer. RSBI values from both methods were compared using paired sample test analysis.
42 patients were enrolled. Two patients with RSBI > 200 by both methods were excluded as non weaning candidates. Baseline patient characteristics are shown in Table 1. Mean RSBI-PSV was 59.40 compared to mean RSBI-SB 72.60. Difference in RSBI-PSV compared to RSBI-SB was 13.20 with SD of 24.74 and SE of mean 3.91. 95% confidence interval for difference was 5.29–21.11. This difference was statistically at P = 0.02. Correlation between RSBI-PSV and RSBI-SB was 0.83. (See Figure 1).
RSBI-PSV are significantly lower, but highly correlated with RSBI-SB (R=0.83).
RSBI-PSV, which is easier to obtain and less stressful on the patient, can be used to predict if the RSBI-SB is in a range associated with successful weaning. Future studies may show that the RSBI-PSV technique could replace the RSBI-SB as a weaning parameter.
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