This is a prospective study consisting in testing whether systematic use of aspirin is beneficial for primary prevention of vascular access for hemodialysis attested by doppler ultrasound exam. The investigators will study aspirin resistance in the population of patients undergoing hemodialysis. The investigators will test sensibility of resistant patients to aspirin dose escalation. PFA-100 is the biologic test used in this study to define aspirin resistance.

Three groups of dialysed patients will be included in this study. The first is the placebo group, the second is the aspirin group fixed dose and the last group includes patients receiving a dose of aspirin titrated by the result of PFA-100.

At the end of this study the investigators will be able to identify whether systematic antiaggregation is suitable for a vascular access for hemodialysis. The investigators will also conclude which is better for patients fixed dose or aspirin dose escalation determined by the result of PFA-100. The study will analyse the prevalence of aspirin resistant patients in this particular population of dialysed patients.

Inclusion Criteria:

• dialysed patients
• vascular access aged less than one year
• no serious complication of the vascular access previously such as hemorrhagic complication and tight stenosis

Exclusion Criteria:

• pregnant and breastfeeding women
• patients receiving at baseline other antiaggregant or anticoagulant
• patient not allowed to be treated by aspirin
• systolic blood pressure> 200 mmhg
• diastolic blood pressure>115 mmhg
• liver failure