Background and Goal of Study. Postoperative cognitive dysfunction (POCD) is a multifactorial event frequently complicating cardiac surgery. The development of POCD may be associated with the perioperative abnormalities of gas exchange, including hyperoxia. Recently, Oxygen Reserve Index (ORI) has been introduced into the clinical practice for non-invasive oxygenation monitoring. The ORI values varying from 0 to 1 correspond to PaO2 of 100–200 mm Hg. The goal of our study was to evaluate whether hyperoxia during cardiac surgery detected by ORI is associated with POCD.
Materials and Methods. Twenty patients who underwent elective off-pump coronary artery bypass grafting (OPCAB) were enrolled into a prospective observational study. Intraoperatively, we measured ORI, hemodynamics and gas exchange at different stages. The cognitive function was assessed using Montreal Cognitive Assessment (MoCA) score at 12 hrs before surgery, and at Days 1 and 5 postoperatively. The decrease in MoCA exceeding 2 pts was interpreted as a cognitive decline. The statistical analysis was performed using Mann-Whitney U-test, Spearman’s rho correlation and ROC analysis. Data are presented as median (25th–75th percentiles). A p value < 0.05 was regarded as statistically significant.
Results and Discussion: Preoperative MoCA score was 24 (22–27) points with significant transient postoperative decrease (p < 0.001) at Day 1 after surgery. We found a correlation of ORI after the recruitment maneuver with MoCA score at Day 1 (rho = –0.60, n = 19, p < 0.007). The ROC-analysis has revealed the cut-off value of ORI exceeding 0.21 as a predictor of early cognitive decline (AUC 0.80, p = 0.01, sensitivity 83 %, specificity 67%). No such a prognostic value for PaO2 198 mm Hg corresponding to ORI 0.21 was found (AUC 0.60, p = 0.2). 
Conclusion. The value of ORI > 0.21 during OPCAB may be a sensitive but non-specific predictor for early POCD. Further evaluation of the role of hyperoxia in development of cognitive dysfunction after cardiac surgery is warranted.


05 / Oxygen reserve index predicts early postoperative cognitive dysfunction in off-pump coronary artery bypass grafting