Cognitive functioning of patients who develop delirium after cardiac surgery

In the present study the cognitive outcomes of cardiac surgery were examined in patients who did or did not develop delirium early post-operatively. The study expanded on previous research by investigating: (1) the relationship between delirium and functioning on specific cognitive domains; (2) the relationship between delirium and cognitive functioning after taking into account pre-existing cognitive impairment; and (3) the cognitive profile of delirium. The study employed a non-equivalent pre-test post-test design. Participants were 80 candidates for coronary artery graft replacement and/ or heart valve repair or replacement operations who were 60 years of age or over. Participants underwent a neuropsychological assessment pre-operatively, daily assessments between postoperative days 2-5 for identification of delirium, and a follow-up neuropsychological assessment 12 weeks post-operation. Twenty-one participants met DSM-IV diagnostic criteria for delirium early post-operation. Participants who experienced delirium performed worse than participants who did not on one global cognitive measure and one specific cognitive domain at follow-up. However, this was likely due to the contribution of other factors such as age, years of schooling, pre-operative performance, and neurological events post-operation. There was no difference in the proportion of participants who did or did not develop delirium who met specified criteria for cognitive decline from pre-operation to follow-up. Significantly more participants who developed delirium, relative to those who did not, met criteria for pre-existing cognitive impairment. After taking into account pre-existing impairment and other potentially contributing variables, delirium was a significant predictor of performance on an attentional task at follow-up. There were no significant differences between the cognitive profiles of participants who did or did not develop delirium, at pre-operation or at follow-up. At both time points the profiles of these groups resembled the profile of a group of patients with vascular dementia. In conclusion, although participants who experienced delirium performed worse on certain cognitive domains, this appeared to be due to factors other than delirium. However, after taking pre-existing cognitive impairment, and other relevant variables into account, delirium adversely affected attentional performance. Delirium was associated with a vascular dementia profile, but this profile was not specific to delirium. Study findings have both theoretical and clinical implications. Consistent with the theoretical literature, the findings support impaired brain reserve as a risk factor for delirium, and the hypotheses that a combination of impaired brain reserve and events associated with delirium are responsible for subsequent cognitive performance. However, in the case of attention, events associated with delirium appear to be responsible for poorer performance, possibly due to the persistence of impaired attention, which is an essential feature of the delirium episode. A further theoretical implication is that individuals who experience delirium may be particularly vulnerable to developing vascular dementia, however, there needs to be further investigation of this risk in a non-cardiac surgery population. Clinically, study findings highlight the need to investigate possible cognitive impairment in individuals with cardiovascular disease, and in persons who experience delirium. When indicated, appropriate monitoring and/ or treatment strategies should be employed to reduce the impact of cognitive deterioration