Objective:In this study, we investigated whether the addition of vitamin B complex to prime solution for cardiopulmonary bypass (CPB) in cobalamin-deficient patients undergoing on-pump coronary artery bypass grafting (CABG) helps prevent the development of postoperative delirium (POD).Materials and Methods:In the present study, 69 of 138 patients with serum vitamin B12levels <200 pg/mL based on the blood sample taken within 1 week prior to on-pump CABG between January 2013 and December 2017 were enrolled. The control group included 69 patients. Vitamin B complex (25 mg vitamin B1, thiamine hydrochloride, 2.734 mg vitamin B2, riboflavin phosphate ester monosodium, 5 mg vitamin B6, pyridoxine hydrochloride, 15 mcg vitamin B12, 50 mg niacinamide, and 17.2 mg D-panthenol) was added to the prime solution for CPB in the study group. The Intensive Care Delirium Screening Checklist (ICDSC) was used for the diagnosis of POD, and the severity of delirium was assessed by using the Delirium Rating Scale-Revised-98 (DRS-R-98).Results:Twenty-nine patients in the control group (42%) and 18 patients (26%) in the study group developed POD(P= .017), delirium severity scores were higher in the control group (16.5 ± 2.9 versus 15.03 ± 2.48,P= .034). Logistic regression analyses showed vitamin B complex was an independent protective factor for preventing the development of POD in patients undergoing on-pump CABG (odds ratio [OR]: 0.23, 95% confidence interval [95% CI]: 0.06-0.83,P= .025).Conclusion:On the basis of the results of our study, the addition of vitamin B complex to the prime solution for CPB decreases the incidence of POD in cobalamin-deficient patients undergoing on-pump CABG.