Role of End-Tidal CO2 During Passive Leg Raising to Predict Fluid Responsiveness in ICU

Inclusion Criteria: * Patients aged 18 years or older. * Patients who have been followed in the intensive care unit (ICU) with mechanical ventilation support for at least 24 hours. * Patients for whom a mini fluid challenge (MFC) is clinically planned by the intensive care team. * Patients for whom informed consent has been obtained from first-degree relatives or a legal representative. Exclusion Criteria: * Patients younger than 18 years of age. * Pregnant patients. * Patients without consent from first-degree relatives or a legal representative. * Patients with known deep vein thrombosis (DVT) in the leg veins (risk of embolism during leg raising). * Patients with pathologies that may cause increased intracranial pressure (e.g., intracranial mass, hemorrhage). * Patients with uncontrolled hypertension. * Patients with severe cardiac disease (e.g., right heart failure, pulmonary hypertension, advanced valvular pathology). * Patients with carbon dioxide (CO2) retention. * Patients who have undergone hip surgery or hip replacement surgery where Passive Leg Raising (PLR) cannot be performed. * Patients with spontaneous breathing. * Patients with a probability of high intra-abdominal pressure. * Patients who cannot lie in a supine position. * Patients with current peripheral oxygen saturation (SpO2) \< 88%. * Patients on mechanical ventilation requiring pressure support \> 16 mmHg or PEEP \> 10 mmHg.