Background: Intra-abdominal pressure (IAP) measurement is used to detect intra-abdominal hypertension (IAH), which may predispose patients to certain physiological derangements of the splanchnic circulation. The patient does not need to be in the supine position for continuous measurement of IAP. Hence, this study evaluated the impact of differing head of bed elevations (HOB) on bladder pressure when used as a surrogate IAP measurement in severely intubated patients. Aim of the study: The aim of the study was to determine the effect of head of bed elevation on intra-abdominal pressure measurement among mechanically ventilated patients. Materials and Method: Research design: the design of this study was a quasi-experimental. Setting: this study was conducted at the general ICU of Damanhur Medical Institute. Subjects: A convenience sample of 60 mechanically ventilated patients was involved. Tool: this study used an assessment tool which consists of four parts; part I: it was used to identify characteristics and clinical data of patients. Part II: this part was used to identify ventilator data. Part III: it was used to identify vital signs which include pulse, temperature systolic, diastolic and mean blood pressure. Part IV: this part was used to identify IAP measurements. Methods: Body mass index (BMI), vital signs, ventilator parameters and Intra- abdominal pressure (IAP) were assessed at different head of bed elevation angles; supine, 15°, 30°and 45°. Results: IAP was found to be increased significantly with increases in HOB angle. Moreover, it was increased significantly, specifically at 45°. Age and BMI positively correlated with IAP with significant differences. Conclusion: There was no difference in the measurement values of IAP: supine position, HOB elevation 15° and 30°. There was a difference in the measurement at 45° position.