The Impact of Olfactory Dysfunction on Post-operative Cognitive Dysfunction and Delirium: A Systematic Review

Abstract

Context: Post-operative cognitive dysfunction (POCD) and postoperative delirium (POD) are common complications following major surgery, particularly in older adults. Emerging evidence suggests that olfactory dysfunction may significantly predispose individuals to these cognitive disturbances, potentially serving as an early marker for post-surgical cognitive decline. However, the relationship between olfactory impairment and post-operative cognitive outcomes remains underexplored. Objectives: The present systematic review aims to synthesize current evidence on the impact of olfactory dysfunction on POCD and POD. Evidence Acquisition: The review adhered to the preferred reporting items for systematic reviews and meta-analyses (PRISMA) guidelines. A comprehensive search of PubMed, Scopus, and the Web of Science (WOS) was conducted from inception until December 2024. Studies on patients undergoing major operations that involved verified olfactory and cognitive examinations and yielded quantitative data were included. Exclusion criteria encompassed research focusing on non-surgical groups, non-original studies, and studies lacking postoperative cognitive assessments. Results: From an initial 389 articles, seven studies met the inclusion criteria, comprising 1,038 participants. These studies, conducted between 2004 and 2022, included patients undergoing major surgeries such as cardiac, abdominal, and neurosurgery. Various olfactory tests [e.g., sniffin’ sticks, brief smell identification test (BSIT)] and cognitive assessments [e.g., mini-mental state examination (MMSE), clock drawing test (CDT)] were used. The findings across studies were heterogeneous but suggested a potential link between olfactory dysfunction and both POCD and POD. Specifically, several studies indicated that impaired olfactory function was associated with an increased risk of delirium (OR = 1.90; 95% CI = 1.17 - 3.09) and cognitive decline post-surgery. Some studies identified olfactory impairment as an independent predictor of worse cognitive outcomes, particularly among frail or elderly populations. Conclusions: The evidence reviewed supports the hypothesis that olfactory dysfunction may be a preoperative marker for POCD, particularly delirium and delayed neurocognitive recovery (dNCR). Based on the obtained results, olfactory testing could be a useful preoperative screening tool, especially in populations at risk for cognitive decline.