Purpose: Intraoperative cerebral tissue inflammation and hypoxia may contribute to neurocognitive disorders following cardiopulmonary bypass (CPB). However, the contributions of general anaesthesia (GA), surgical trauma and CPB are unclear. Methods: In adult female sheep, we investigated the systemic inflammatory response, cerebral tissue oxygenation and the extent of microglia activation (biomarker of neuroinflammation) across cerebral cortical regions during GA and surgical trauma with and without CPB (N=5-10/group). Sheep were studied while conscious, during GA and surgical site injury, with and without CPB. Results: Plasma TNF-alpha (3.7 [1.4] vs. 1.6 [0.9] ng/mL; mean [standard deviation]; P=0.0004), and IL-6 levels (4.0 [2.1] vs. 1.5 [0.9] ng/mL; P = 0.029) were significantly higher at 1.5 hours, with a further increase in IL-6 at 3 hours (7.0 [3.7] vs. 1.8 [0.9] ng/mL; P<0.0001) in animals undergoing CPB compared with those that did not. Although cerebral oxygen saturation and cerebral tissue oxygen tension were preserved throughout CPB, histology showed pronounced neuroinflammation with greater microglia circularity within the frontal cortex of sheep that underwent CPB compared with those that did not (0.34 [0.02] vs. 0.30 [0.01]; P = 0.029). Moreover, microglia had fewer branches within the parietal (7.7 [1.0] vs. 10.9 [1.3]; P = 0.001) and temporal (7.8 [0.5] vs. 9.9 [1.4]; P= 0.020) cortices in sheep that underwent CPB. Conclusion: CPB enhanced the release of pro-inflammatory cytokines beyond that initiated by GA and surgical trauma. This systemic inflammation was associated with widespread neuroinflammation despite an absence of cerebral hypoxemia. The frontal, parietal and temporal cortices appear to be particularly susceptible to neuroinflammation during CPB. These data provide direct evidence of CPB-induced neuroinflammation in a large animal model and provide further mechanistic data on how CPB-induced cerebral inflammation might drive postoperative neurocognitive disorders in humans.