Fig. 2.

Mechanisms of PND. A Gut microbes can communicate with the central nervous system through neural, immune and endocrine pathways (gut-brain axis) and affect brain function. A gut microbial imbalance can damage the intestinal barrier, cause metabolic abnormalities, and lead to neuroinflammation. B The immune vascular hypothesis states that innate immune disorders might adversely affect the blood–brain barrier and cause POD in patients. C Surgery under anaesthesia can induce neuroinflammation and activate astrocytes and microglia, thus causing neuronal damage