The autonomous nervous system and the cholinergic anti-inflammatory reflex in postoperative neurocognitive disorders

Purpose of review Postoperative delirium (POD) is a common and serious complication after surgery. It is associated with postoperative neurocognitive disorder (PNCD). The vagal cholinergic anti-inflammatory pathway (CAP) has been hypothesized to play a role in POD/PNCD and may be a target for interventions such as transcutaneous auricular stimulation (taVNS). We aim to review associations of heart rate variability (HRV) as an indicator of vagal function with POD and postoperative immune reaction as well as taVNS as a potential preventive intervention for POD. Recent findings Autonomous nervous system (ANS) dysfunction was a common finding in studies analysing HRV in POD and postoperative cognitive dysfunction, but results were heterogeneous. There was no evidence from HRV analysis that vagal activity prevents overshooting postoperative immune activation, but HRV may help to identify patients at risk for postoperative infections. Animal studies and preliminary trials suggest that taVNS may be used to prevent POD/PNCD. Summary Our review provides no evidence that CAP suppression is associated with POD/PNCD. Future studies should consider that high vagal tone may also mediate immunosuppression in surgical patients, yielding an increased risk for postoperative infections. Although taVNS is a promising approach to prevent POD/POCD, future studies should take these concerns into account.