Disturbances in Oxygen Balance During Cardiopulmonary Bypass: A Risk Factor for Postoperative Delirium

Objective: The aim of this study was to determine risk factors for postoperative delirium after cardiac surgery, specifically associated with the conduct of cardiopulmonary bypass (CPB).

Design: Prospective observational study.

Setting: Heart Centre, University Hospital.

Participants: The study included 142 patients aged 70 years and older scheduled for elective cardiac surgery with CPB.

Interventions: Risk factor analysis comprised information collected from the hospital clinical and CPB dedicated databases in addition to the medical chart. Delirium was diagnosed according to the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision criterion using the Mini Mental State Examination and the Organic Brain Syndrome scale.

Measurements and main results: Assessments of delirium diagnosis were executed preoperatively and on the following first and fourth postoperative days. Delirium occurred in 55% (78/142) of the patients. Patients with delirium were identified with significantly higher body weight and body surface area preoperatively, accompanied with longer CPB time, higher positive fluid balance per CPB, and lower systemic pump flow related to body surface area. Furthermore, the duration of the mixed venous oxygen saturation (S_vO₂) below 75% was significantly longer during CPB. The result from the multivariable logistic regression analysis included the duration of S_vO₂ below 75%, fluid balance per CPB and patient age as independent risk factors for postoperative delirium.

Conclusions: The influence of the S_vO₂ level during CPB, fluid balance, and patient age should be recognized as risk factors for postoperative delirium after cardiac surgery in patients 70 years and older.