Aim: This study evaluates the impact of monitoring a primary quality indicator and the effect of training on improving the care and maintenance of vascular access devices. Design: A prospective, quasi-experimental, multicentre study with 10 periodical cross-sections from 2017 and 2020. Participants: Adult patients hospitalised over 24 h, with or without vascular access device, excluding those in emergency, psychiatry, outpatients or minor surgery units. Methods: The study included 10 cross-sections between 2017 and 2020 in all participating hospitals, using the INCATIV® (Quality Indicators in Intravenous Therapy and Vascular Access) questionnaire. Training sessions for nursing staff were conducted between cross-sections, involving face-to-face sessions in open classrooms and clinical sessions in the units, based on the study Care bundle. Results: 53,991 vascular accesses were analysed, with an average INCATIV Index score of 8.95 (SD: 1.32), showing improvement from 8.09 in the first cross-section to 9.21 in the last. Significant variability was observed between hospitals, with secondary hospitals scoring lower on the INCATIV® Index. Training interventions 1 and 2 showed significant improvement across all hospital categories, whereas intervention 5 did not show significant effects. Compliance with main recommendations was studied, with a notable decrease in phlebitis rates from 4.45% in the first cross-section to 1.23% in the tenth. Conclusion: The study developed a single indicator to assess and quantify vascular access care quality. It demonstrated that implementing a care bundle through serial training interventions and continuous assessment by nursing staff, supported by process indicators and data availability on the study platform, significantly reduces complications and enhances the quality and safety of vascular access care.