A commentary on “Progress of research in postoperative cognitive dysfunction in cardiac surgery patients: A review article” [Int. J. Surg. 95 (2021) 106163]

Dear Editor Bhushan et al. [1] recently published a review article on postoperative cognitive dysfunction (POCD) after cardiac surgery in International Journal of Surgery. In this review, the authors systematically searched related studies and showed factors which were associated with POCD after cardiac surgery. Undoubtedly, the authors’ great contribution provides an extremely important basis for prevention and reduction of POCD after cardiac surgery. However, the following points deserve further clarification. First, the Bhushan’s study [1] described alcohol abuse, gender, duration of surgery, blood loss, and hemoglobin to be associated with POCD after cardiac surgery. However, the authors failed to provide relevant references which can lead to confusion. In the absence of such references, readers cannot trace the original articles, thus making it challenging to judge whether the statements by the authors are correct or not. In our view, such appropriate references should have been included in the article. In addition, Hudetz et al. [2] have previously published a study on alcohol dependence and POCD after cardiac surgery which showed that patients with a history of alcohol dependence had an increased incidence and severity of POCD after cardiac surgery. As this study was not referred to by the Bhushan’s study [1], there might well be a potential retrieval bias. Second, as an important aim of a review article is to summarize previous published evidences on a topic which hopefully can lead to better use of these evidences in clinical practice. Common clinical parameters associated with POCD after cardiac surgery should be included in a review article. Renal function is a commonly used clinical parameter and it has been shown to be associated with mortality and poor outcomes in patients with heart failure [3,4]. A study [5] on 88 patients after elective coronary artery bypass graft (CABG) surgery was done to determine the risk factors associated with POCD, and the results showed that renal failure (OR, 2.8; 95% CI, 2.4–4.3) to be associated with an increased incidence of POCD after 6 months of follow-up, indicating that attempts in stabilizing renal functions can help to reduce the incidence of POCD after cardiac surgery. Third, the relationship between inflammatory factors and POCD after cardiac surgery should not be entirely ignored. A previous study showed that cardiac surgery caused extensive systemic inflammatory response, which is currently believed to be due to activation of the immune system in blood circulation [6]. With damage or destruction of the blood-brain barrier, inflammatory factors can spread to the brain, resulting in increased incidences of POCD. Furthermore, previous studies have also shown that cytokine interleukin-6 [7] and C-reactive protein [8] to be associated with increased POCD after cardiac surgery, which further support the role played by inflammatory factors on POCD. Such evidences can lead to further refinement of risk stratification for POCD based on levels of inflammatory factors. Provenance and peer review Commentary, internally reviewed.