The Influence of Cardiopulmonary Bypass on the Incidence of Postoperative Delirium in Cardiac Surgery

Background: The incidence of postoperative delirium (POD) following cardiac surgery is rising as a result of increased age and complexity of patients. The ensuing problems are not only costly, but are commonly associated with long-term morbidity and increased mortality. We conducted a case–control study to assess the contribution of cardiopulmonary bypass (CPB) to the development of POD.

Method: A database was compiled from three datasets of patients who underwent cardiac surgery between 2014 and 2019: ICU discharge files, CP protocols, and medical quality management records. Only successfully matched patients were included. Those patients, who required surgical revision at the same hospitalization, were excluded. Raw data were extracted and structured via algorithms implemented in Python. Multiple imputation filled in missing data. Ten independent imputations were analyzed by multiple logistic regression with step-wise deletion of factors to arrive at a minimal adequate model.

Results: POD occurred in 456/3,163 patients (14.4%). In addition to well-established demographic risk factors promoting POD (male sex, age, acute renal failure, diabetes mellitus, emergency, right heart failure), complexity of procedures expressed by longer aortic cross-clamp times were associated with the occurrence of POD (OR: 1.661; CI: 1.384–1.994). Regression analysis of CPB parameters showed that higher minimal blood flow was protective against POD (odds ratio [OR]: 0.83; 95% confidence interval [CI]: 0.739–0.932). On the contrary, flow rates of at least 30% above the required pump flow rate were also associated with a higher risk for POD (OR: 2.508; CI: 1.375–4.574). A higher minimum arterial pH coincided with a higher risk of POD (OR: 1.777; CI: 1.096–2.880).

Conclusion: CPB steering and execution has a tremendous effect on the occurrence of postoperative delirium. Both hypo- and hyperperfusion can cause POD. Especially prolonged low pump flow rates may lead to the consumption of cerebral blood flow reserves and consequently to POD. Strict adherence to perfusion limits and tighter control of blood flow and acid–base balance during CPB may help further decrease the risk of POD.

Publication History

Article published online:
03 February 2022