Olfactory enrichment mitigates delayed neurocognitive recovery after major orthopaedic surgery in older patients: A...

Delayed neurocognitive recovery (dNCR) is a prevalent complication in older patients undergoing surgery. It may progress to long-term cognitive impairment and increase the risk of Alzheimer's disease.

This study aimed to evaluate the effects of olfactory enrichment on dNCR and to examine the association between olfactory function and dNCR.

This sham-controlled, assessor-blind, parallel-group randomised trial enrolled 149 participants aged 65 or older undergoing elective total knee or hip replacement under general anaesthesia. Participants were assigned to either the olfactory enrichment group or the sham group. The intervention group received daily olfactory enrichment from 3 days preoperatively to 7 days postoperatively. Cognitive function was evaluated using a neuropsychological test battery 3 days before and 7 days after surgery. Olfactory identification ability was assessed by five-odour olfactory detection arrays. Propensity score matching analysis was employed to mitigate potential confounding and selection bias.

A total of 131 patients completed the study (62 in the olfactory enrichment group and 69 in the sham group). The overall incidence of dNCR was 26.7% (35 out of 131). In the intention-to-treat analysis, the difference between groups was not statistically significant (19.4% vs. 33.3%; χ ² = 3.259; p = 0.071). However, in the 1:1 propensity score-matched cohort (n = 82), the incidence of dNCR was significantly lower in the olfactory enrichment group than in the sham group (12.2% vs. 39.0%; χ ² = 7.476; p = 0.005). Raw postoperative cognitive scores and individual change scores did not differ between the groups. Participants with decreased olfactory identification scores (n = 32) had a significantly higher incidence of dNCR than those with stable or improved scores (40.6% vs. 22.2%; χ ² = 4.183; p = 0.041).

In older patients undergoing major orthopaedic surgery, perioperative olfactory dysfunction is associated with an increased risk of dNCR. Olfactory enrichment may represent a potential nonpharmacological strategy for reducing postoperative cognitive decline in this population.