OBJECTIVE: Unsuccessful extubation from mechanical ventilation increases mortality and morbidity. Therefore, the identification of an accurate predictor of successful extubation is desirable. This study was designed to determine whether the results of easily performed respiratory measurements, particularly if reported as "combined extubation" indices, were better predictors of extubation failure in a pediatric population than were readily available clinical data. DESIGN: Prospective observational study. SETTING: Tertiary pediatric intensive care unit. PATIENTS: All children who required mechanical ventilation for >/=24 hrs during a 12-month period and whose parents gave informed written consent. INTERVENTIONS: Respiratory function measurements were made (on average) 7 hrs (range, 0.2-25.0 hrs) before extubation. Arterial blood gas results were obtained immediately before extubation. The values of each predictor associated with maximum sensitivity and specificity were determined, and the areas under receiver operator characteristic curves were compared to determine the most accurate predictor of successful extubation. MEASUREMENTS AND MAIN RESULTS: A total of 47 children (mean age, 3.90 yrs; range, 0.10-17.3 yrs) were studied; extubation failed in 7. A low tidal volume (<7.5 mL/kg) and a low minute volume (<250 mL/kg) had the highest sensitivities (86% and 71%, respectively) and specificities (61% and 71%, respectively) in predicting extubation failure. The a/A ratio performed least well in predicting extubation failure (area under the receiver operating characteristic curve, 0.51). CONCLUSIONS: Volume measurements during pediatric mechanical ventilation may facilitate successful extubation.