AIM: It is necessary for an effective NIV application to provide proper modality selection, sufficient minute ventilation (MV), also the amount of leakage on the circuit must be minimized and patient-ventilator adaptation must be achieved. METHODS: 30 patients with acute respiratory failure as a result of either internal or postoperative reasons were included in the study. Patient comfort was analyzed with a scale ranging from 0 to 2. Firstly the patient was used for two hours in BIPAP modality, after then the AVAPS modality (Period Av) was applied by setting the required rates the same mask. During BIPAP and AVAPS, arterial blood gases analysis, comfort scale and hemodynamic parameters were recorded in the 30th minute, 1st hour and 2nd hour. RESULTS: According to the assessment of arterial blood gases, the pH changes of both periods were statistically significant compared to their baseline values (p=0.001). Treatment compliance of the patients was significantly better at AVAPS modality at all times (p = 0.015, p = 0.008, p = 0.008, respectively). CONCLUSIONS: According to the results obtained from this study, the AVAPS modality has positive effects on pH and gas variation and patient comfort; therefore, it can be confidently used in clinical practice.