Conclusions

This retrospective cohort analysis demonstrates that postoperative anaemia severity is a critical, independent predictor of 30-day adverse outcomes, including prolonged hospitalisation, unplanned readmission and mortality, in patients undergoing vascular surgery. A distinct dose-dependent gradient was identified, with moderate and severe postoperative anaemia precipitating a four- to 10-fold increase in short-term complications. This risk trajectory is heavily driven by procedural physiological stress, as evidenced by the significant association between open surgical interventions and worse outcomes. While preoperative or persistent perioperative anaemia exhibited weaker, less consistent associations, it is the synergistic impact of an invasive open approach and profound postoperative anaemia that dictates a poor patient trajectory. Future prospective, multicentre studies incorporating intraoperative blood loss, patient frailty, and transfusion data are warranted to validate these findings and establish optimal postoperative intervention thresholds.