Methods: Children with AHRF (oxygenation index ≥10) aged between one month and 14 years under CMV with PEEP≥10cmH2O and 5ppm iNO for 1h were randomly assigned to CMV (CMVG, n=12) or HFV (HFVG, n=12) in a crossover design. Children with chronic cardiac or pulmonary diseases were excluded. Patients were kept under one of the two ventilation modes for 8h, crossing to the other for 8h, and then back again to complete 24h observation. Blood gas analysis, oxygenation indexes, and hemodynamic variables were recorded at enrollment (Tind), 1h after iNO start and then every 4h (T4h etc). The Mann-Whitney U test compared group ages and PRISM scores, and the Fisher test genders. Moments and groups were compared by repeated measure analysis for independent groups. Significance was considered at p<0.05.