The weaning index as predictor of weaning success.

BACKGROUND: The quest to obtain an accurate way to predict success when weaning a patient from mechanical ventilation continues. The established parameters such as tidal volume (Vt), respiratory rate (f), negative inspiratory force (NIF), vital capacity (VC), and minute ventilation (V) have not predicted weaning accurately. The frequency-to-tidal volume ratio (f/Vt), or rapid shallow breathing index (RSBI) is a good predictor of weaning success if the value is low, but not when the value approximates 105. Because of the aforementioned, we decided to add 2 corrective factors to the RSBI. The first one was elastance index (EI = peak pressure/NIF) and the second one, the ventilatory demand index (VDI = minute ventilation/10). The result of the product of the RSBI × EI × VDI was called the weaning index (WI). METHODS: In order to assess the discriminatory power of WI, we obtained weaning parameters and calculated WI for 59 patients in our intensive care unit and extubated them if RSBI was ≤105. Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and receiver-operating characteristics (ROC) curves were obtained. The results were compared with the previous studies involving the RSBI. RESULTS: The WI sensitivity was 98%, specificity was 89%, PPV was 95%, NPV was 94%, and area under the ROC curve was 95.9. CONCLUSIONS: The WI is a simple and reproducible parameter that integrates breathing pattern, compliance, inspiratory muscle strength, and ventilatory demand and is the most accurate predictor of weaning success.

The lung permeability index: a feasible measurement of pulmonary capillary permeability.

BACKGROUND: We performed this study to determine the pulmonary capillary permeability (PCP) measuring radiolabeled human serum albumin leakage into the lung. The objective was to use PCP to differentiate between cardiogenic and non-cardiogenic pulmonary edema etiologies. METHODS: We conducted this study in 10 patients admitted to the intensive care unit who had recently developed bilateral pulmonary infiltrates and required hemodynamic monitoring. In these patients we determined the association among the lung permeability index, cardiac output, pulmonary capillary wedge pressure, myocardial performance index, and the protein content of the bronchoalveolar lavage as expressed by bronchoalveolar lavage (BAL) total protein and BAL-to-serum protein ratio. Twenty mCi of technetium-labeled albumin was injected and measure in the heart and the lung at 10 and 180 min post-injection. Lung and heart uptake ratios as well as the lung permeability index were calculated. RESULTS: We found a good correlation between the lung permeability index and both the myocardial performance index (cardiac output/pulmonary capillary wedge pressure) and the total protein content of the bronchoalveolar lavage fluid. CONCLUSION: The lung permeability index is a feasible, noninvasive estimation of the pulmonary capillary permeability.