Determining the best threshold of rapid shallow breathing index in a therapist-implemented patient-specific weaning protocol.

BACKGROUND For weaning patients from prolonged mechanical ventilation, we previously designed a respiratory-therapist-implemented weaning protocol that decreased median weaning time from 29 days to 17 days. An acceleration step at the start of the protocol allowed patients with a rapid shallow breathing index (RSBI) of < or = 80 to advance directly to spontaneous breathing trials (SBTs). METHODS We prospectively evaluated whether calibrating the RSBI threshold allowed more patients to safely accelerate to the 1-hour SBT in the protocol, and whether that correlated with weaning duration and outcome. If the patient passed the clinical stability screening, the respiratory therapist calculated the RSBI and then attempted a 1-hour SBT. If the pre-SBT RSBI was > 80, the SBT was attended by an investigator, with continuous electrocardiography and pulse oximetry. This SBT was followed by continued weaning efforts, as dictated by the weaning protocol. The data were analyzed using receiver operating characteristic curves and univariate and multivariate analyses. RESULTS One hundred ninety-one patients (with a wide range of RSBIs [10 to 1,248]) underwent 1-hour SBT, of whom 26 failed weaning and 165 succeeded. RSBI correlated with 1-hour SBT outcome; the area under the receiver operating characteristic curve was 0.844. Plotting the sensitivity and specificity together against RSBI allowed calibration of the RSBI threshold to the desired level of false positives and false negatives. Accuracy was maximized (81.7%) at an RSBI of 97. Tolerance of a 1-hour SBT, using the new RSBI threshold, correlated with duration of weaning and weaning outcome. CONCLUSIONS The conservative RSBI threshold of </= 80 can be raised for patients weaned with our respiratory-therapist-implemented weaning protocol. The optimal RSBI threshold was 97, where accuracy was maximal. RSBI was a good predictor of 1-hour SBT tolerance in this cohort of tracheotomized patients weaning from prolonged mechanical ventilation.