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

Abstract

Dear Editor, Neurocognitive complications are a major concern after cardiac surgery, and postoperative cognitive dysfunction (POCD) has been observed in 23–81% of these patients [1,2]. POCD should not be overlooked as a transient phenomenon as it has been shown to be related to decreased quality of life. It is very important to identify patients at risk for POCD and to focus preventive strategies. Bhushan et al. [3] reviewed the progress in diagnosis, pathogenesis and risk factors and control strategy of POCD. They found that the highest POCD incidence was observed after open aortic, transthoracic aortic valve implementation and coronary artery bypass grafting surgery. Age, cognitive function, depression, cardiopulmonary bypass (CPB) and anesthetic use are leading risk factors. Currently, a very decisive hypothesis of POCD development includes systemic inflammatory response syndrome (SIRS) induced by cardiac surgery and CPB. The latter causes specific activation of inflammatory response by the immune system following contact between blood and artificial materials of the bypass circuit, by ischemia-reperfusion injury, by complement activation, and by heparin neutralization with protamine. In contrast, cardiac surgery nonspecifically initiates an inflammatory response. Significantly, Parolari et al. [4] reported similarity of the inflammatory marker levels after cardiac surgery with or without CPB, whereas several recent studies demonstrated that avoiding CPB does not improve cognitive functions (up to class-1 evidence) [5]. As impaired cerebral autoregulation prompted by surgical procedure may contribute to intraoperative cerebral ischemia, this mechanism has also been proposed as a significant part of POCD development. The understanding of POCD has expanded significantly since the first reports back in the 1970. We, therefore, must reevaluate our knowledge to overcome the present gaps and set directions for future research. As POCD investigators are faced with a methodological mixture of cognitive impairment definitions that may have crucial impacts on the study findings, this issue requires attention. Recent findings suggest that inflammatory response plays an important role in the complex pathogenesis of POCD. However, future researches must provide more insights about the role and association of inflammation with other mutually interdependent mechanisms that underlie POCD development. To better illustrate the importance of this topic for researchers, the effects of numerous interesting interventions with different classes of evidence have been described in the literature on cognitive functions, predominantly through their anti-inflammatory activity, such as the effects of valerian root, minocycline, statins, lidocaine, noble gas xenon, and others. Gerriets et al. [6] proposed that an obligatory neuropsychological evaluation prior to cardiac surgery is a good investment of time and money to detect at-risk patients. Indeed, a short preoperative cognitive training regime may reduce POCD rates. Provenance and peer review Not commissioned, Editor reviewed. Ethical approval No Ethical Approval was given. Sources of funding NA. Author contribution Shuai Shi: comment the paper. Qingqiang Yang: review. Shouling Huang: study design. Research registration Unique Identifying Number (UIN) Unique Identifying Number (UIN): NA. Trial registry number – ISRCTN NA. Guarantor Shuai Shi. Declaration of competing interest No conflict of interest.