Rapid shallow breathing index and weaning outcome in cardiovascular surgery patients requiring mechanical ventilation for 24 hours or longer

The purpose of this prospective descriptive study was to investigate the differences between the rapid shallow breathing index (RSBI) measured at 2 different time points for cardiovascular surgical patients who have a positive weaning outcome and those that do not. The study was conducted in a 52-bed cardiovascular recovery room (CVRR) in a tertiary care teaching institution located in the south central portion of the US. Twenty-nine consecutive patients undergoing cardiac surgery on cardiopulmonary bypass were enrolled. All measures of the RSBI were obtained with the Wright respirometer while the patient was breathing spontaneously. The first RSBI (RSBI1) was measured at 24 hours or when the patient was stable on mechanical ventilation per the study protocol. The second measure (RSBI2) was obtained at the beginning of the first weaning trial. Of the total sample (N = 29), 24 cases had a positive weaning outcome, defined as the ability to breathe spontaneously for 24 hours after weaning, compared to 5 cases that had a negative weaning outcome. Data were analyzed using two independent t-tests that compared mean differences of the RSBI measures between the positive and negative weaning outcome groups. The assumption for homogeneity of variance was tested and found to be met prior to conducting the t=tests. There was a significant difference between the weaned and the non-weaned groups for the RSBI 1 (t=-6.414, df=27, p=0.000). RSBI means were significantly higher for the group with a negative weaning outcome. In addition, the RSBI at the time of weaning (RSBI 2) was statistically significant indicating that the mean RSBI scores were higher for the non-weaned group (t=-8.404, df=27, p= .000). The results of this study indicate that the RSBI may be useful in predicting weaning outcome in cardiovascular surgery patients.