Abstract
IntroductionIndexes predicting weaning outcome are frequently inaccurate. We developed a new integrative weaning index aimed at improving the accuracy of the traditional indexes.MethodsThree hundred and thirty-one patients mechanically-ventilated for more than 24 hours were evaluated. Initially, the threshold values of each index that best discriminate between a successful and an unsuccessful weaning outcome were determined in 115 patients. In the second phase, the predictive performance of these values was tested prospectively in the other 216 patients. Frequency/tidal volume ratio (f/Vt ratio), tidal volume (Vt), tracheal airway occlusion pressure 0.1 s (P 0.1), the product of P 0.1 and f/Vt (P 0.1 × f/Vt), respiratory rate (f), static compliance of the respiratory system (Cst,rs), ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2 ratio) and the new integrative weaning index IWI (Cst,rs × arterial oxygen saturation/f/Vt ratio) were evaluated in all patients. The readiness for weaning and the decision to return to mechanical ventilation was made by the physician in charge, based on the signs of poor tolerance. The receiver operating characteristic (ROC) curves were calculated in order to evaluate the predictive performance of each index. The Bayes' theorem was used to assess the probability of each test of predicting weaning.ResultsIn the prospective-validation set, successful weaning was observed in 183 patients (84.7%) and weaning failure in 33 (15.27%). IWI presented the highest accuracy, with the area under the ROC curves larger than that under the curves for the f/Vt ratio (0.96 × 0.85 respectively; P = 0.003), and also larger than that under the curves for the other indexes. IWI presented a higher probability of successful weaning when the test was positive (0.99) and a lower probability when the test was negative (0.14). Measurement of Cst,rs during the weaning process was considered one of the study limitations.ConclusionsIWI was the best predictive performance index of weaning outcome and can be used in the intensive care unit setting.Trial Registrationcontrolled-trials.com ISRCTN92117906
Highlights
Indexes predicting weaning outcome are frequently inaccurate
Discontinuation from mechanical ventilation was attempted when the physician in charge judged that the patient was ready to be weaned, according to the following criteria: the cause for starting mechanical ventilation had resolved or at least improved; body temperature was below 38.5°C; hemoglobin was equal to or higher than 8 g/dl; and none or a minimal dose of vasoactive or sedative drugs was administered
The objective of this study is to test the predictive performance of a new integrative weaning index (IWI)
Summary
Indexes predicting weaning outcome are frequently inaccurate. No weaning predictive index has proven to be ideal [1]. According to the Sixth International Consensus Conference on Intensive Care Medicine [2], patients who meet the following satisfactory criteria should be considered ready for weaning: frequency to tidal volume ratio (f/Vt) less than 105 breaths/min/L, respiratory rate (f) of 35 breaths/min or less, maximal inspiratory pressure (MIP) of -20 or less to -25 cmH2O, tidal volume (Vt) more than 5 mL/kg, vital capacity more than 10 mL/kg, and arterial oxygen saturation (SaO2) above 90% with a fraction of inspired oxygen (FiO2) of 0.4 or less (or partial pressure of arterial oxygen (PaO2)/FiO2 ratio of 150 mmHg or above). After the assessment of these indexes regarding readiness for weaning, a spontaneous breathing trial (SBT) should follow as a diagnostic test to determine the likelihood of successful extubation [3]. Several predictors of weaning are used to aid decision-making [2]
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