A new integrative weaning index of discontinuation from mechanical ventilation
© BioMed Central Ltd 2005
Published: 9 June 2005
Background and objectives
Indexes predicting the weaning outcome are frequently inaccurate. With the present study, we aim to evaluate the predictive performance of a new index for predicting the weaning outcome, which we called the integrative weaning index (IWI).
Two hundred and fifty patients of several etiologies in the weaning process that remained up to 24 hours in mechanical ventilation were evaluated (all with PaO2 ≥ 60 mmHg with FiO2≤ 0.4 and PEEP ≤ 8 cmH2O). All patients were submitted to a 2-hour trial of spontaneous breathing. Those who sustained 2 hours of spontaneous breathing without return to mechanical ventilation in the following 24 hours were considered weaned, while those who could not sustain 2 hours of spontaneous breathing or returned to mechanical ventilation in the following 24 hours were considered not weaned. The frequency/tidal volume ratio (f/Vt ratio), the airway occlusion pressure at 0.1 s after the onset of inspiratory effort (P 0.1), the product of P 0.1 and f/Vt (P 0.1 × f/Vt), the respiratory rate (RR), the quasi-static compliance of the respiratory system (Cqst,rs), the PaO2/FiO2 ratio and the new integrative weaning index (IWI = Cqst,rs × SaO2 / f/Vt ratio) were evaluated in all patients. Arterial blood gas was collected with FiO2 in 0.35. The sensitivity, specificity, positive predictive value, negative predictive value and the receiver operating characteristic (ROC) curves were calculated in order to evaluate the predictive performance of each index. The nonparametric method of Hanley and McNeil was used to compare the area under the ROC curves of each index.
Two hundred and eighteen patients were weaned, while 32 patients were not weaned. The IWI presented the larger area under the ROC curves (0.97), followed by the f/Vt ratio (0.90), Cqst,rs (0.89), f/Vt × P 0.1 (0.85), RR (0.80), P 0.1 (0.70) and finally by the PaO2/FiO2 ratio (0.60). The area under the ROC curves of the IWI was larger than those for f/Vt ratio (P < 0.0001) and also larger than those for the other indexes (P < 0.0001).
In our study, even compared with other essential indexes in the literature, the IWI showed the best criteria for predicting the weaning outcome. With the obtained results we believe that with the use of the IWI in other countries we may further prove its accuracy.