SERIAL MEASUREMENTS OF THE RAPID-SHALLOW-BREATHING INDEX AS A PREDICTOR OF WEANING OUTCOME IN ELDERLY MEDICAL PATIENTS

Study objectives: To determine the usefulness of serial measurements o f the rapid-shallow-breathing index (f/VT) as a predictor for successf ully weaning elderly medical patients fr om mechanical ventilator supp ort using a threshold value (less than or equal to 130) derived specif ically for this population. Design: Prospective observational study us ing parameters suggested from retrospective analysis. Setting: Medical ICUs of a university-affiliated private teaching hospital. Patients: Using data obtained from a retrospective analysis of 10 medical patien ts greater than or equal to 70 years old who had failed weaning, 49 ad ditional medical patients older than 70 years were studied prospective ly. Interventions: Standard weaning parameters were determined using a hand-held spirometer. Respiratory rate (f, breaths/min) and tidal vol ume (VT, liters) were measured at the beginning of a spontaneous breat hing trial and hourly thereafter for up to 5 h using the same hand-hel d spirometer. Measurements ann results: Retrospective analysis showed that the published threshold value for f/VT (less than or equal to 105 ) had poor predictability for weaning success when measured at the beg inning of the weaning trial. In the 9 of 10 patients who failed to wea n in the retrospective review, the f/VT increased to >130 as tile tria l progressed over 2 to 3 h. Using an f/VT less than or equal to 130 as the threshold value for prospectively predicting successful weaning, the diagnostic accuracy, sensitivity, specificity, positive predictive value, and negative predictive value increased from 84%, 92%, 57%, 87 %, and 67%, respectively, when measured at the beginning of the weanin g trial to 92%, 93%, 89%, 97%, and 80%, respectively, when measured 3 h later. The area under the receiver operating characteristic curve fo r f/VT also improved from 0.81 to 0.93. Conclusions: Serial measuremen ts of the rapid-shallow-breathing index in medical elderly patients du ring a period of spontaneous breathing can accurately predict the abil ity to be successfully weaned from mechanical ventilator support.