Introduction: Treatment of patients with acute respiratory failure (ARF) often involves mechanical ventilation via endotracheal intubation. Non-invasive positive pressure ventilation (NIV) using Bilevel positive airway pressure (BiPAP) can be a safe and effective means of improving gas exchange, avoiding incidence of complications associated with invasive mechanical ventilation and decreasing length of hospital stay.Objective: 1) To assess non-invasive positive pressure ventilation (BiPAP) as an alternative way for ventilation in ARF. 2) To determine factors that can predict the successful use of BiPAP.Patients and methods: Thirty patients with acute respiratory failure (both type I and type II) were enrolled in the study and divided into two groups. Group I included 10 patients who were subjected to invasive mechanical ventilation. Group II included 20 patients who were subjected to NIV using BiPAP. Both groups were compared regarding the following parameters: arterial blood gases on admission, 30 minutes after beginning of mechanical ventilation, 1 ½ hour and once daily, complications namely ventilator associated pneumonia (VAP), skin necrosis, CO2 narcosis, static compliance and resistance were measured at day one and day two.Results: Compared to group I, group II patients were associated with similar improvement in ABG data at 30 minutes and at discharge. Variable½ An hourDiscontinuation of VentilationInvasiveN=10Non-invasiveN=20P-valueInvasiveN=10Non-invasiveN=16P-valuepH7.31±0.027.33±0.030.2077.42±0.047.42±0.030.799PCO265.55±12.6865.71±13.290.97551.34±7.2250.21±5.990.672PO293.8±6.4195.04±28.770.89567.25±9.1368.96±11.380.692SO295.50±0.9794.00±5.810.42892.38±2.5193.5±2.780.311PO2/FIO2184.92±19.96198.94±14.040.500321.27±43.89327.83±57.350.760Group II (NIV) showed significantly lower incidence in VAP (20% vs 80%) compared to group I, skin necrosis (50%), CO2 narcosis (20%) occurred in group II only. Shorter duration of mechanical ventilation (3±3 vs 6±5 days, P = 0.006), and shorter length of hospital stay (5.8±3.6 vs 8.9±2.7 days, P = 0.011) when compared to group I. Group II patients showed significant difference change in compliance and change in resistance from day I to day II when compared to group I. InvasiveP-valueNon-InvasiveP-valueDay I Day IIDay IDay IICompliance38.92±11.5948.55±7.630.000149.85±8.4866.93±8.040.0001Resistance16.140±6.2711.00±2.490.00019.75±3.613.12±1.400.0001On univariate basis parameters were analyzed to choose those who were associated with outcome in concern (successful NIV). The following parameters were identified level of consciousness, pH (7.3±0.03 vs 7.26±0.1, P = 0.009) PCO2 (69.16±13.14 vs 100.97±12.04) on admission, 1 ½ hour after NIV, pH (7.37±0.03 vs 7.31±0.17, P = 0.005), PCO2 (53.98±8.95 vs 77.47±5.22, P = 0.0001) in whom succeeded and failed NIV respectively. Then multivariate analyzed utilizing two different techniques namely (multivariate logistic regression and discriminant analysis) was used. The variable identified was PCO2 after 1½ hour in the two models with specificity 100%.Conclusion: In patients with acute respiratory failure, non-invasive ventilation was as effective as conventional ventilation in improving gas exchange, associated with fewer serious complications and shorter stays in intensive care. One and half hour trial with NIV can predict success with BiPAP, as shown by an improvement in pH and PCO2 and overall clinical picture. PCO2 after 1½ hour could be the sole predictor of successful NIV with 100% specificity.