Neuronal damage biomarkers in the identification of patients at risk of long‐term postoperative cognitive dysfunction after cardiac surgery

Biomarkers of neurological injury can potentially predict postoperative cognitive dysfunction. We aimed to identify whether classical neuronal damage‐specific biomarkers, including brain fatty acid‐binding protein, neuron‐specific enolase and S100 calcium‐binding protein β, as well as plasma‐free haemoglobin concentration as a measure of haemolysis, could be used to predict the risk of long‐term cognitive decline after coronary artery bypass grafting with or without cardiopulmonary bypass. We assessed cognitive function using the CogState brief computerised cognitive test battery at 3 months and at 15 months after surgery. Blood samples were obtained pre‐operatively, after sternal closure, and at 6 h and 24 h postoperatively. We found signs of cognitive decline at 3 months in 15 of 57 patients (26%), and in 13 of 48 patients (27%) at 15 months. Brain fatty acid‐binding protein was already significantly higher before surgery in patients with postoperative cognitive dysfunction at 15 months, with pre‐operative plasma levels of 22.8 (8.3–33.0 [0–44.6]) pg.ml^?1 compared with 9.7 (3.9–17.3 [0–49.0]) pg.ml^?1 in patients without cognitive dysfunction. This biomarker remained significantly higher in patients with cognitive decline throughout the entire postoperative period. At 3 months after surgery, high levels of plasma‐free haemoglobin at sternal closure were associated with a negative influence on cognitive performance, as were high baseline scores on neuropsychological tests, whereas a higher level of education proved to beneficially influence cognitive outcome. We found that postoperative cognitive dysfunction at 3 months was associated with cognitive decline at 15 months after surgery, and served as a valuable prognostic factor for declines in individual cognitive performance one year later. Classical neuronal injury‐related biomarkers were of no clear prognostic value.