What is this study about? We are studying whether the Pleth Variability Index (PVI)-a simple, non-invasive measurement from a pulse oximeter-can help predict low blood pressure (hypotension) during routine maintenance hemodialysis. Low blood pressure during dialysis is a common and potentially serious complication. Our goal is to find out if monitoring PVI can help identify patients at risk, so that early action can be taken. Who can join? Adults aged 18 to 80 years. Patients who have been receiving maintenance hemodialysis regularly for more than 3 months. Those who are willing and able to participate and sign an informed consent form. Who cannot join? Patients with severe heart rhythm problems, severe peripheral circulation problems, or swelling that makes PVI measurement unreliable. Patients who are pregnant or breastfeeding. Patients allergic to the dialysis filter or unable to cooperate with the study procedures. What will happen during the study? PVI Measurement: Your PVI will be checked with a simple fingertip device before starting dialysis and again 30 minutes after dialysis begins. Blood Pressure Monitoring: Your blood pressure will be closely watched throughout the dialysis session. Data Collection: Information about your age, medical history, medications, lab results, dialysis settings, and other standard measurements will be recorded. What are the benefits and risks? Benefits: By identifying patients at higher risk for low blood pressure during dialysis, the study may lead to safer and more comfortable dialysis treatment in the future. Risks: All measurements used in this study are safe and non-invasive, with no extra risk compared to routine care. Your Rights and Safety Participation is completely voluntary-you may leave the study at any time without affecting your medical care. The study has been reviewed and approved by the hospital's ethics committee. Your privacy and personal data will be strictly protected.