Is Crystallised Intelligence Preserved in Post-Operative Delirium?

Objectives: Performance on the National Adult Reading Test (NART), a test of Crystallised Intelligence (Gc), is generally preserved in chronic cognitive decline, for instance dementia. In contrast, performance on tests of fluid cognitive function (FCF) diminishes. The present study assessed whether a similar pattern of Gc/FCF performance is found during an instance of acute cognitive decline, post-operative delirium. Subjects and Methods: 37 cardiac surgery patients (26 male, 11 female; M = 70.5 years, SD = 7.3 years) completed both pre- and post-operative testing sessions (S1 and S2). Tests consisted of two parts; a “Cognitive Test Battery”, comprising of the NART, as a measure of Gc, and Digit Span, Verbal Fluency and the Victoria Stroop Test as measures of FCF, and a “Delirium Assessment Battery”. Results: 9 participants developed post-operative delirium (POD), 28 did not (NPOD). POD participants’ performance on all FCF tests declined in S2, and scores were worse than NPOD participants’. Group by Session interactions were significant in Digit Span Backward (p = .014) and tended towards significance in Verbal Fluency (p =.077) and Digit Span Forward (p = .059). Change scores (S2-S1 difference) differed significantly for Stroop W, Stroop C and Stroop Score (p =.003, p < .001, and p = .001 respectively). Stroop D change scores were non-significant (p = .23). In contrast, NART scores neither decreased significantly post-operatively, nor differed significantly between POD/NPOD groups (Group x Session interaction; p = .71). Conclusions: The current study found NART performance, as a measure of Gc, was preserved in POD, while performance on FCF tests declined. Performance patterns on FCF tests differed between POD and NPOD groups. This reflects similar findings in chronic cognitive decline