The Science Journal of the American Association for Respiratory Care

2006 OPEN FORUM Abstracts

COMPARSIONS OF RAPID SHALLOW BREATHING INDEX, ADVERSE REACTIONS, AND PREDICTIVE ACCURACY IN THE SAME PATIENT GROUP WITH AND WITHOUT VENTILATORY SUPPORT

Mauo-Ying Bien PhD RPT RRT, Yu Ru Kou PhD, Huei-Guan Shie MPH RRT, You-Lan Yang MS, Chung-Hung Shih, MD PhD, Jia-Horng Wang MD, Kuo-Chen Cheng MD. School of Respiratory Therapy, Taipei Medical University, Taipei, Taiwan, R. O. C.

Background: The rapid shallow breathing index (RSBI) measured during spontaneous breathing has been widely used as a predictor for weaning outcome. RSBI can be measured when patients are disconnected from the ventilator (RA-no ventilator) or are still connecting to the ventilator. So far, there is no study comparing the RSBI values, the incidence of adverse reaction, and the predictive accuracy measured by these two methods. This study was conducted to compare these clinical endpoints under the conditions of RA-no ventilator and 4 different settings of ventilatory support before weaning trials in the same patient group.

Methods:
98 mechanically ventilated medical patients ready for weaning were included. They were divided into success (n=71) and failure (n=27) groups based upon their weaning outcome. Before weaning, spontaneous minute ventilation and respiratory frequency were measured for 1 minute, and average tidal volume and RSBI were calculated under 5 conditions: RA-no ventilator; FiO2: 21%, CPAP: 0 or 5 cmH2O; and FiO2: 40%, CPAP: 0 or 5 cmH2O. The sequences of the conditions were randomized and at least 5 minutes were elapsed between any 2 conditions. After the patients successfully completely the weaning trials, they were extubated. Successful weaning was defined as patients free from the ventilator for over 48 hours. Friedman repeated measures analysis of variance on ranks and Dunn's method were used to compare the RSBI values. The predictive performances of the RSBI measured in 5 conditions, their pair wise comparisons, and the most appropriate cut-off values were assessed by analysis of the receiver operating characteristic (ROC) curve. Data are presented as mean ± SD. P < 0.05 was considered significant.

Results:
The RSBI values measured under 4 conditions of ventilator settings were higher than that of RA-no ventilator. The changes in pulse rate and blood pressure post-measurement were within the clinically acceptable ranges, but the incidence of occurring respiratory rate ³ 35/min or oxygen saturation £ 89% (adverse reaction) was highest under the conditions of 21%-0 cmH2O and 21%-5 cmH2O and lowest under the condition of 40%-5 cmH2O. The areas under ROC curve measured under these 5 conditions were within the range of 0.51-0.62 indicating their predicative accuracy; no significant difference was detected between any 2 conditions. The RSBI values of 91 and 105 breaths/min/L under the conditions of RA-no ventilator and 40%-5 cmH2O, respectively, were the optimal cut-off values in this patient group.

  RR, b/min VE, LPM VT, L RSBI, b/min/L Adverse Reaction
RA-no ventilator 23.29 ± 6.24 7.93 ± 2.61 0.352 ± 0.112 74.54 ± 33.53 16
21%-0 cmH2O 24.88 ± 6.26 7.26 ± 2.41 0.307 ± 0.126a 97.51 ± 50.25a 20
21%-5 cmH2O 24.06 ± 5.80 7.15 ± 2.24a 0.310 ± 0.112a 90.28 ± 43.64a 20
40%-0 cmH2O 24.12 ± 5.86 7.14 ± 2.25a 0.309 ± 0.110a 92.01 ± 51.19a 4
40%-5 cmH2O  23.27 ± 5.88b,c 6.85 ± 2.36a,b,c 0.308 ± 0.120a 91.53 ± 53.74a 2


avs. RA-no ventilator, bvs. 21%-0 cmH2O, and cvs. 40%-0 cmH2O in the same parameters, P < 0.05

Conclusions: While no difference in predicting weaning outcome can be found among 5 conditions studied, the RSBI value measured under the condition of RA-no ventilator is the lowest. Changes in FiO2 and CPAP settings have no effect on RSBI measured by the ventilator methods. Ventilator methods with FiO2 21% have high incidence of adverse reaction.

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