Postoperative anaemia and long-term survival following cardiac surgery: a multicentre, retrospective, observational...

Pre-operative anaemia is associated with adverse outcomes following cardiac surgery. However, the prognostic impact of postoperative anaemia is characterised incompletely. We examined whether anaemia at hospital discharge independently predicts long-term survival and characterised haemoglobin recovery trajectories during the first postoperative year.

This retrospective multicentre cohort study included 25,697 adult cardiac surgery patients from two Danish tertiary centres (2000-2024). Anaemia was classified using World Health Organization sex-specific criteria as mild (haemoglobin 110-129 g.l^-1 for men; 110-119 g.l^-1 for women) or moderate-severe (haemoglobin < 110 g.l^-1 for both). The primary outcome was overall survival from surgery to death or censoring at end of follow-up. Cox proportional hazards regression assessed associations between anaemia at discharge and mortality, adjusting for age, sex, pre-operative haemoglobin and comorbidities. Restricted cubic splines examined non-linear relationships between haemoglobin and mortality.

At discharge, 23,935 (93.1%) patients were anaemic (8384 (32.6%) mild anaemia and 15,551 (60.5%) moderate-severe anaemia). Moderate-severe anaemia was independently associated with worse survival (hazard ratio 1.11, 95%CI 1.01-1.21, p = 0.034) in adjusted analysis. Cubic spline analysis revealed a steep, non-linear relationship between pre-operative haemoglobin and mortality, whereas discharge haemoglobin provided limited prognostic information beyond baseline characteristics and surgical complexity. Haemoglobin recovery plateaued around 4 months after discharge, but the average haemoglobin level remained below baseline even after 1 year.

Postoperative anaemia showed a weak independent association with long-term mortality, in contrast to the clear dose-response relationship observed for pre-operative anaemia. The near-universal prevalence of postoperative anaemia and incomplete haemoglobin recovery at 1 year support further trials of peri-operative anaemia management.