Objective criteria to predict extubation outcome in mechanically ventilated children are not available. Our goal was to study factors associated with extubation success and to evaluate the usefulness of the rapid shallow breathing index (RSBI) and the compliance, resistance, oxygenation, and pressure index (CROP index) in children. Data were prospectively collected on 227 mechanically ventilated children. Patients successfully extubated had significantly better lung compliance (Cdyn: 0.59 +/- 0.91 versus 0.39 +/- 0.14 ml/kg/cm H(2)O), higher Pa(O(2))/FI(O(2)) ratio (382.4 +/- 181.2 versus 279.8 +/- 93.9), and lower Pa(CO(2)) (41.3 +/- 6.7 versus 47.3 +/- 8.5 mm Hg). Spontaneous breathing parameters showed significantly lower respiratory rates (RR) (36.6 +/- 17.9 versus 52.8 +/- 23 breaths/min), larger tidal volumes (VT) (7.3 +/- 2.6 versus 4.9 +/- 1.8 ml/kg), and greater muscle strength (negative inspiratory force [NIF]: 41.8 +/- 15.4 versus 35.1 +/- 12.5 cm H(2)O) in successfully extubated children. Extubation failures had higher RSBIs and lower CROP index values. A RSBI value of </= 8 breaths/ml/kg had a sensitivity of 74% and specificity of 74%, whereas a CROP value of >/= 0.15 ml/kg/breaths/min had a sensitivity of 83% and specificity of 53% for extubation success. Children failing extubation demonstrate abnormalities of respiratory function. The RSBI and CROP index are useful to predict pediatric extubation success.