Dementia and postoperative outcomes in older adults: national estimates and mechanistic pathways from a US cohort...

As populations age, increasing numbers of older adults with dementia undergo surgery. Although dementia is associated with worse postoperative outcomes, the pathways through which dementia confers surgical risk remain poorly understood.

We conducted a retrospective cohort study using the American College of Surgeons National Surgical Quality Improvement Program database (2021-2024). Adults aged ≥75 years undergoing surgery were included. Multivariable regression and marginal standardisation were used to estimate adjusted risk ratios (aRRs) and absolute risk differences for 30-day mortality and secondary outcomes, including postoperative delirium, loss of independence (LOI), prolonged length of hospital stay and new institutionalisation. Causal mediation analyses decomposed total effects into natural direct and indirect effects through postoperative delirium and LOI.

Among 547 310 older adults undergoing surgery, 43 041 (7·9%) had preoperative dementia. After adjustment, dementia was associated with higher 30-day mortality (aRR 1·64, 95% CI 1·50-1·80), increased postoperative delirium (aRR 3·09) and greater LOI (aRR 1·24), but not with surgical complications (aRR 1·02). Delirium mediated 46·0% (95% CI 38·6-55·9) of the dementia-associated mortality risk, while LOI mediated 26·0% (22·7-30·2). LOI accounted for most of the effect on prolonged hospitalisation (42·6%) and new institutionalisation (70·2%), whereas delirium explained only a small proportion of LOI (14·2%). Dementia-associated mortality was most pronounced among patients with lower frailty and in elective surgical settings.

Dementia influences postoperative outcomes through distinct, pathway-specific mechanisms. Mortality is driven primarily by postoperative delirium, whereas healthcare utilisation is largely mediated by loss of functional independence.