Creation of Arteriovenous Fistulas for Hemodialysis Using the End-to-side Anastomotic Technique vs. Piggyback.

Inclusion Criteria: * Age \> 18 years * Able to meet protocol requirements, including follow-up. * Incident or prevalent patient with advanced chronic kidney disease in the hemodialysis stage (stage 5D). * In predialysis patients (stage 5), if renal replacement therapy (hemodialysis) is anticipated to be required within the next 6 months (based on standard clinical criteria). * Who, based on their associated pathology and according to medical criteria, can withstand the initial surgery and arteriovenous access maintenance procedures. * Have a current ultrasound with preoperative venous and arterial mapping. * Meet the anatomical requirements for AVF creation: * Wrist: artery \>2 mm, vein \>2 mm in diameter * Elbow: artery \>3 mm, vein \>3 mm in diameter * Absence of arterial calcification or occlusion, or other aberrant arterial anatomy. * Adequate arterial and venous patency. * Vein-to-skin distance \<5 mm. * Candidate for creation of a native arteriovenous fistula for hemodialysis, either distal (radiocephalic) or proximal (humerocephalic or humerobasilic). * No immediate transplant scheduled within the next 60 days (inclusion on the kidney transplant waiting list is not a contraindication for entry into the study, nor for the creation of an arteriovenous fistula). * No prior arteriovenous surgeries in the same or proximal location. * Correct understanding of the study conditions and acceptance to participate. Exclusion Criteria: * Pregnant women. * Life expectancy \<1 year. * Arteriovenous prostheses (non-native fistulas), previous arteriovenous fistula repairs, arteriovenous accesses created in the lower extremities, and unusual (exotic) accesses. * Known or suspected central venous stenosis/occlusion on the side of the planned access. * Repair of previous arteriovenous accesses (proximal reanastomoses). * Biological immunosuppression. * History or evidence of serious systemic illness, including: * Cardiac disease (New York Heart Association functional class III or IV, as evidenced by the inability to lie still), myocardial infarction within 6 weeks prior to randomization, ventricular tachyarrhythmia requiring ongoing treatment, or unstable angina. Suspected or documented hypercoagulable or hypocoagulable state or Clinically significant active infection (White blood count \> 15,000 cells/mm3) other than the use of a treated CVC. * Any other condition that, in the investigator's judgment, prevents an adequate evaluation of the safety and efficacy of the study or poor compliance. * Patient unwilling or unable to attend follow-up follow-ups.