Incident dementia or cognitive decline after elective surgery in older adults: highlighting the importance of shared decision-making

With the exponentially rising number of older adults with healthcare needs and elective surgeries, there is an insurgence of aging in the United States and across the globe.¹ The number of total joint arthroplasties among older adults alone in the U.S. is estimated to grow by 71–85% to 635,000 procedures annually for total hip replacements and 1.26 million procedures for total knee replacements, by 2030.² Older adults are also more likely to need other surgeries due to pathophysiological aging, including inguinal hernia repair, prostatectomies and hysterectomies.

At the same time, the number of older adults living with cognitive impairment has been rising internationally – with notable morbidity, caregiver burden and economic cost.³ Specifically, postoperative neurocognitive disorders occur in 10–30% of older patients after non-cardiac surgery.⁴ Long-term cognitive decline is itself associated with morbidity and mortality which can pre-empt the benefits of elective surgery (improvement in pain, mobility, etc).⁵ Thus, researchers and policy makers have been examining and developing interventions for the potentially modifiable risk factors for postoperative neurocognitive disorders.³ These risk factors include surgery type, anesthesia, delirium and pain control. And yet, cognitive changes remain the most common complication after surgery and are associated with poor clinical outcomes, such as mortality, functional decline and ultimately, neurodegenerative dementia.^4,6 This has deterred some older adults from seeking surgical management despite being appropriate candidates who may benefit from the procedures. The correlation and significance of cognitive decline after major surgery with anesthesia remains unclear and the pathophysiological mechanisms have not been elucidated. These relationships warrant urgent exploration, in an aging population where elective surgery is becoming increasingly relevant.

In this issue of the Journal of the American Geriatrics Society, Reich et al.⁷ and Tang et al.⁸ examine this important and interesting topic of whether there is an association between elective surgery and incident dementia or long-term cognitive decline. The authors are to be commended for tackling this complex subject where there is much heterogeneity in patient population and contributing risk factors. Reich et al. examine the rate of incident dementia in older adults who underwent common elective surgeries. In this large study of over 27,000 Canadian patients using propensity-score matching, they did not find an increased rate of incident dementia when comparing elective surgery patients with matched non-surgical controls over 5 years of follow up. Tang et al. examine cognitive decline in older adults undergoing total joint arthroplasty (TJA), with and without osteoarthritic pain. They found no clinically or statistically significant acceleration in memory decline at 3 and 5 years, compared to non-surgical controls, after TJA in a United States population-based cohort from the Health and Retirement Study.

Both studies, in fact, found a reduced rate of incident dementia or memory decline by 5 years in the surgical patients compared with their control counterparts. Reich et al. was able to confirm the persistence of this association in subgroup and sensitivity analysis – accounting for mortality, regional vs. general anesthesia, and dementia diagnosis within 90 days of elective surgery (to rule out prolonged delirium misclassified as dementia).⁷ Tang et al. also confirmed their findings with post-hoc difference-in-differences analysis, factoring in aging, frailty and presence of pain – with the rationale that persistent pain can impact cognition and mood in older adults.⁸ Thus, the authors of both studies demonstrate cautious and restrained approaches to interpreting their provocative data. They do not overclaim the benefits of elective surgery for this heterogeneous age demographic. Instead, Reich et al. and Tang et al. emphasize the complexities of cognition as well as aging pathophysiology and the dynamic nature of frailty. Their results are reassuring regarding the risks and potential benefits of elective surgery for older adults. But the authors highlight the importance of individualized shared decision-making with older adults contemplating surgery.

In the current literature on cognition and surgery among older adults, one common study limitation is the relatively short duration of follow-up. Postoperative cognitive decline by 12 months after surgery has been well-established in the literature, with over 30% of older adults undergoing TJA affected.⁹ What happens longer term, however, has not been fully explored until now, raising questions as well as exciting possibilities as to whether elective surgery can improve more than just physical function. Both Reich et al. and Tang et al., were able to examine the three and five-year trajectory for their cohorts. Reich et al. also examined whether anesthesia type affected longer term incident dementia.⁷ Tang et al. examined whether chronic pain affected longer term cognitive decline.⁸

There are limitations to both studies. Tang et al. uses a summary measure for cognitive tests from the Health and Retirement Study and this “memory score” may be artificially derived. The authors did validate this score, and demonstrate it was carefully thought-out. Whether “three months of memory decline” is clinically significant enough to be considered abnormal, however, may require future examination and replication.⁸ Reich et al. matched their surgical patients to patients who did not pursue elective surgery after surgical consultation. The reasons for not proceeding with surgery were not examined; this thus begs the question whether there were cognitive concerns that led patients to choose non-surgical treatment, which can in turn affect the study results.⁷ Furthermore, neither study examined delirium incidence which is a well-established source for post-operative cognitive decline.¹⁰ Reich et al. attempted to address this by excluding patients with dementia diagnosis within 90 days after elective surgery, considering delirium may have been misclassified as dementia. This, however, would mainly capture patients with prolonged delirium.

Reich et al. also used a retrospective cohort that was more homogeneous (ethnically and racially) and assumed the effect of surgery on dementia is fixed when it likely is dynamic. The study cohort was clinically stable patients able to weigh the risks and benefits of an elective procedure, not patients needing emergency surgery when they are clinically unstable and undergoing a heterogeneity of inflammatory stressors. The shared decision-making around elective surgery and its potential effects on cognition is likely different from the pressing decisions and factors around emergent surgery. Tang et al. used a cohort that included underrepresented older adults, ethnically, racially and socioeconomically. However, neither study had detailed cognitive and medical complexity data available on their patients from before elective surgery.^7,8

It is refreshing to see both Reich et al. and Tang et al. take away from their studies the importance of counseling older adults before elective surgery. Their work adds an important piece to the puzzle of geriatric surgical care. Both authors highlight the complexities of cognition, the dynamic aging process and the pathophysiological impacts of surgery. In this way, their studies will inform clinicians to engage their older patients in shared decision-making to determine the best, individualized treatment plans. Reich et al. and Tang et al. lay important groundwork in the causal link between surgery and cognition, and pave the way for exciting future interventions for maintaining brain health. These may include prehabilitation to preserve function, intensive pain control peri-operatively and ongoing prevention and treatment of delirium. This knowledge and future interventions will help guide clinical decisions and reduce the deeply personal and broadly societal impact of both surgical complications and cognitive decline.