Background: Despite the fact that mechanical ventilation is an essential part in management of critically ill patients, mechanically ventilated patients have a higher risk of complications, which can lead to increased morbidity and mortality. Objective: This study aimed to study the effect of training inspiratory muscle through modifying mechanical ventilator (MV) trigger sensitivity on arterial blood gases in mechanically ventilated patients. Patients and Methods:Sixty adult patients diagnosed with acute respiratory failure, needed to be intubated and connected to mechanical ventilated. They were from both gender and their ages ranged from 50 to 70 years. The patient were chosen from Intensive Care Unit (ICU), Department of Chest Diseases, Cairo University Hospitals. They were randomly assigned into two equal groups. Group (A): included thirty patients who received training for inspiratory muscle through modifying MV trigger sensitivity plus usual physical therapy. Group (B): included thirty patients who received usual physical therapy only. Results: The results showed a significant increase in partial arterial pressure (PaO₂) in both groups, this increasing was significantly higher in patients who received training for the inspiratory muscle plus the usual chest physical therapy than patients who only received usual chest physical therapy (P-value < 0.001). The results showed no significant change in neither power of hydrogen (pH) nor partial pressure of carbon dioxide (PaCO₂).Conclusion: Training to inspiratory muscles in mechanically ventilated patient through modifying mechanical ventilator trigger sensitivity can produce a significant increase in partial arterial pressure (PaO₂). Although it has no effect in pH nor PaCO₂.