Fluid management in critically ill patients, particularly those with severe traumatic brain injury (TBI), septic shock, and acute respiratory distress syndrome (ARDS), presents a complex and multifaceted challenge. Dynamic tests such as the end-expiratory occlusion (EEO) test and tidal volume challenge (TVC) test are commonly used to assess fluid responsiveness, providing valuable insights into cardiovascular responses to changes in volume status. However, due to the unique risks and complications associated with these conditions, there is an increasing need to explore and evaluate alternative methods for predicting fluid responsiveness more safely and accurately in these critically ill patients.This study presents a prospective investigation conducted on patients with severe TBI, septic shock, and ARDS. Before administering a 100 mL colloid bolus, both the EEO and TVC tests were performed. Initial measurements of cardiac output (CO), cardiac index (CI), and pulse pressure variation (PPV) were recorded, followed by subsequent measurements after each test to assess the fluid responsiveness and cardiovascular changes in these critically ill patients.Among the 180 participants, a more than 5% increase in CI during the EEO test was indicative of fluid responsiveness. Similarly, a 3.5% absolute increase in PPV during the TVC test suggested fluid responsiveness. The interrater reliability for the EEO test was observed to be 0.915, indicating strong agreement between raters, while for PPV, it was 0.637, reflecting moderate agreement. These values suggest that the EEO test shows a high degree of consistency between different evaluators, whereas the PPV measurement demonstrates a more moderate level of reliability.In patients with severe TBI, septic shock, and ARDS who are receiving low tidal volume (VT) ventilation, both the EEO test for 15 seconds and the TVC method can be used to assess fluid responsiveness. However, it is important to note that the EEO test demonstrates greater reliability in this context.