Association of Postoperative Nadir Haemoglobin Levels With Long-term Adverse Events After Elective Noncardiac Surgery

AIM: Preoperative anaemia is a well-established risk factor for poor outcomes. However, the impact of postoperative haemoglobin (Hb) levels on long-term outcomes, including mortality and cardiovascular events, remains uncertain. This study aims to assess the independent association between postoperative nadir Hb levels and long-term outcomes, considering the potential interaction with preoperative anaemia status. METHODS: This study is a secondary analysis of data from the Myocardial Injury in Noncardiac Surgery in Sweden study, which included patients aged ≥50 years undergoing elective noncardiac surgery. Postoperative Hb levels were measured daily for up to 3 days or until discharge, and the lowest recorded value was used as the primary exposure variable. Multivariable logistic regression analysis was employed to explore the independent association of postoperative nadir Hb with the primary outcome of a composite endpoint comprising all-cause mortality and cardiovascular complications over a one-year period, adjusting for a range of perioperative risk factors, including preoperative anaemia. To account for a potential interaction with preoperative anaemia, an interaction term was added to the model. Secondary outcomes were one-year mortality and one-year cardiovascular morbidity. RESULTS: A total of 1284 patients were included, of whom 521 (40.6%) had preoperative anaemia. The median postoperative nadir Hb level was 102 g·L–1 (interquartile range 92–114). Postoperative nadir Hb was not independently associated with the composite primary outcome; however, it showed a weak but statistically significant association with one-year mortality (adjusted odds ratio aOR 0.98, 95% confidence interval CI 0.95–0.99). No significant interaction was found between preoperative anaemia and postoperative nadir Hb. Independent predictors of the primary outcome included university hospital status (aOR 2.83, 95% CI 1.96–4.10), age (aOR 1.05, 95% CI 1.03–1.07), and unplanned postoperative intensive care (aOR 3.17, CI 1.08–9.28). CONCLUSIONS: Postoperative nadir Hb levels, within the observed range well above 70 g·L-1, were not independently associated with the long-term composite outcome. However, they were weakly associated with one-year mortality. No significant interaction was found between preoperative anaemia and postoperative nadir Hb. These findings highlight the need for further investigation into the clinical significance of postoperative Hb levels in high-risk patients.