Cognitive and brain reserve and the risk of postoperative delirium in older patients: analysis of data from a prospective observational study

Abstract

Background Cognitive and brain reserve theories suggest that aspects of neural architecture or cognitive processes modify the impact of neuropathological processes on cognitive outcomes. While frequently studied in the context of dementia, reserve in delirium is relatively understudied. Methods We examined the association of three markers of brain reserve (head circumference, MRI-derived brain volume, and leisure time physical activity) and five markers of cognitive reserve (education, vocabulary, cognitive activities, cognitive demand of lifetime occupation, and interpersonal demand of lifetime occupation) and the risk of postoperative delirium in a prospective observational study of 566 older adults free of dementia undergoing scheduled surgery. Findings Twenty four percent of patients (135/566) developed delirium during the postoperative hospitalization period. Of the reserve markers examined, only the Wechsler Test of Adult Reading (WTAR) was significantly associated with the risk of delirium. A one-half standard deviation better performance on the WTAR was associated with a 38% reduction in delirium risk (P = 0·01); adjusted relative risk of 0·62, 95% confidence interval 0·45–0·85. Interpretation In this relatively large and well-designed study, most markers of reserve fail to predict delirium risk. The exception to this is the WTAR. Our findings suggest that the reserve markers that are important for delirium may be different from those considered to be important for dementia.

The Cognitive Reserve Model in the Development of Delirium: The Successful Aging After Elective Surgery Study

“…Our dementia-free cohort allowed us to test the reserve hypothesis for delirium while minimizing the potential for confounding by pre-existing dementia. Although the relationship between reserve and postoperative delirium has been reported previously [15, 16, 47, 48], the formal test of the reserve hypothesis demonstrating effect modification between pathology and postoperative delirium -- has not been tested previously. The evidence for the existence of effect modification in our study may form the basis of future studies elucidating the role of reserve in delirium.…”

“…Jones et al reported higher risk of delirium in those with lower educational levels [15]. Saczynski et al did not find a correlation between the risk of delirium and traditional cognitive and brain reserve markers of education, cognitive activities, and head circumference; but the Wechsler Test of Adult Reading (WTAR), a measure of vocabulary knowledge, was associated with delirium risk [16]. It is important to note, however, that these studies do not comprise a formal test of reserve theory in delirium.…”

Genetic and environmental factors associated with delirium severity in older adults with dementia

“…The results of this study extend the findings of other investigations of APOE and delirium. While previous studies have yielded mixed results, it has been suggested that the observed association between APOE and delirium may be attributed to the pathologic vulnerability that occurs in individuals with preexisting dementia (Saczynski et al ., ). For example, APOE ε4 is the most robust genetic risk factor for an accelerated cognitive decline in individuals with Alzheimer's disease (AD) (Lim et al ., ; Carrasquillo et al ., ), and this may be related to a heavier burden of AD pathology in ε4 carriers (Farfel et al ., ).…”

“…() report that higher education was associated with lower incidence of delirium in older adults. Similarly, higher scores on verbal intelligence testing were associated with lower delirium risk in older adults undergoing surgery (Saczynski et al ., ). We previously reported a protective effect of occupational attainment in individuals with dementia (Massimo et al ., ); therefore, we sought to incorporate this factor in the current investigation.…”

The short‐term and long‐term relationship between delirium and cognitive trajectory in older surgical patients

“…26 The GCP, which is sensitive to change with minimal floor and ceiling effects, 26,27 has been applied in prior studies. 27,29–31 …”