Knowing the predictors of NPPV failure in patient with ARF is therefore crucial in deciding if and when to apply this ventilatory technique. Several authors have identified different predictive factors of NPPV failure in children with ARF: the results of studies are given in Table 3 [20, 24, 26, 27, 31, 54, 55] . The best predictive factors for the NPPV failure in ARF appear to be the level of FiO 2 and PaCO 2 on admission or within the first hours after starting NPPV (Table 3) .