Background: Postoperative delirium (POD) is a neurocognitive syndrome affecting patients undergoing surgery. It is a frequent complication of coronary artery bypass grafting (CABG) and is associated with higher morbidity, mortality and treatment costs. This study aimed to investigate the relationship between gaseous microemboli (GME) load during cardiopulmonary bypass (CPB) and subsequent POD in patients undergoing CABG. Methods: In total, 102 patients undergoing elective on-pump CABG were evaluated in this observational study. An ultrasonic microbubble counter, with probes placed on the arterial and venous lines, was used during CPB to evaluate the GME load for each patient. During the first postoperative week, the patients were examined for the presence of POD. Results: Patients diagnosed with POD had higher number of bubbles in the arterial CPB line (5382.8 (4127.8–6637.8) vs. 2389.4 (2033.9–2745.0), p < 0.001), higher volume of bubbles in both the venous (24.2 µL (16.8–31.6) vs. 12.4 µL (9.7–15.1), p = 0.004) and arterial lines (1.82 µL (1.43–2.21) vs. 0.29 µL (0.22–0.36), p < 0.001), lower quality factor (QF) values (p = 0.039), a lower venoarterial reduction in bubble number (83.0% (77.8–88.1) vs. 92.4% (90.9–93.8), p = 0.001) and a lower venoarterial reduction in bubble volume (88.8% (85.4–92.2) vs. 96.3% (95.2–97.3), p < 0.001) compared to the patients without POD. Older age (p = 0.005), a lower reduction in bubble volume (p < 0.001) and lower QF values (p = 0.004) were significant independent predictors of POD. Conclusions: Our findings indicate a strong association between GME and the occurrence of POD, which entails that all available actions should be implemented to prevent their generation and facilitate the elimination of GME from the CPB circuit.

The increasing preference for off-pump coronary artery bypass grafting (CABG) reflects efforts to reduce complications associated with cardiopulmonary bypa