Objective criteria for ending mechanical ventilation have not been established for infants and children. A recent study in adult patients developed two new indexes, the Rapid Shallow Breathing Index (RSB) and the CROP Index for predicting success or failure of extubation. We decided to evaluate the applicability of these indices to intubated, mechanically ventilated pediatric patients. For this evaluation the indices were adapted to the physiology of infants and children. A pneumotachograph was used to measure spontaneous tidal volume, respiratory rate and dynamic compliance. The tidal volume and the dynamic compliance were corrected for the patient's body weight. Based on the data collected a cutoff value for each index was determined. Of 47 sets of patient data, 38 (81%) were collected during successful extubations, 9 (19%) during failed extubations. A modified CROP index value of > or = 0.1 ml x mmHg/bpm/kg and a modified RSB index value of < or = 11 bpm/mlkg were identified as predictive of successful extubation. The modified CROP cutoff value produced a sensitivity and specificity of 1.0; respective values for the modified RSB cutoff value are 0.79 and 0.78. Cutoff values of > or = 0.1 and < or = 11 for the modified CROP index and RSB index, respectively, appear to be predictive of successful extubation in the pediatric population. Our data identifies the modified CROP index as a superior discriminator between successful and unsuccessful extubation.