Objective. To analyze the characteristics of patients younger than 2 years old who had a moderate to severe acute lower respiratory tract infection and were treated early with bubble continuous positive airway pressure, and factors associated with a successful intervention. Method. Retrospective and descriptive study. Children younger than 2 years old admitted to the Pediatric Intermediate Care Unit of Hospital Provincial Neuquén between June 2009 and December 2010. Bubble continuous positive airway pressure was used, and the following outcomes were measured: heart rate, respiratory rate, Tal's score, oxygen saturation, and fraction of inspired oxygen at 0, 2, 6, 24, and 48 h. Results. One hundred and twenty patients were included. Their median age was 3 months old. The intervention was successful in 72% of patients. At 2 h, a 15% reduction in respiratory rate, and a 2-point decrease in Tal's score were predictors of success, with an odds ratio of 6.41 (95% confidence interval: 2.68-15.36), and of 9.07 (95% confidence interval: 3.72-22.19), respectively. Conclusions. A reduction in respiratory rate, heart rate, and Tal's score at 2 hours of starting the intervention were predictors of success.