“I’m most afraid of losing my mind. You lose your identity, your sense of who you are, where you are.” – Stephen King
- Delirium is a neurobehavioural syndrome that presents clinically with acute confusion, inattention, disorganized thinking, and fluctuating mental status.
- Predisposing factors: older age, alcohol use, & poor functional and cognitive status.
- Patients who have delirious episodes are more likely to have long term cognitive decline.
- To examine the association between cognitive status and post-operative delirium (POD) in elderly patients who underwent surgery.
- To validate previous findings that the rate of POD is increased in patients who have a clinical diagnosis of mild cognitive impairment (MCI) or dementia at the time of surgery.
- Surgical patients who are cognitively normal, who develop POD are at increased risk for subsequent development of MCI or dementia.
- All patients > 65 years old, exposed to any type of anaesthesia and enrolled in The Mayo Clinic Study of Aging (MCSA) between 29.11.04 and 26.03.14.
- Retrospective single-centre cohort study.
- Assessment of cognition at enrolment and every 15 months (including risk factor questionnaires for neurological conditions e.g. pre-existing dementia, neuropsychological testing and apolipoprotein E genotyping).
- Assessment of delirium using CAM-ICU on hospital admission, then every 12 hours, and if there was any alteration to mental status. Postoperative delirium was defined as a CAM-ICU positive event that occurred within the first 72 h after surgery.
- Exclusion criteria: Patients who had at least one CAM-ICU positive score for delirium before surgery and patients with RASS score -4 or -5.
- Statistical analysis using multivariate logistic regression.
- 2014 patients (4 excluded due to pre-operative delirium).
- Type of anaesthesia: GA (53%), Monitored anaesthesia care (39%), RA (8%).
- The frequency of POD was significantly higher in patients with prevalent MCI/dementia compared with those who were cognitively normal (8.7 vs 2.6%; P<0.001).
- After adjustment for potential confounders, pre-existing MCI/dementia remained significantly associated with an increased risk for delirium – [OR, 2.53 (95% CI, 1.52–4.21); P<0.001].
- The frequency of MCI/dementia at the first follow-up was significantly higher in patients who experienced POD vs those who did not (33.3 vs 9.0%; P<0.001).
- After adjustment for other potential confounders, POD remained significantly associated with an increased risk for subsequent diagnosis of MCI/dementia [OR, 3.00 (95% CI, 1.12–8.05); P=0.03].
- Elderly patients with MCI at the time of surgery are at higher risk for clinically evident POD compared with patients without MCI.
- Elderly patients who are cognitively normal before surgery and who experience clinically evident POD are more likely to develop MCI or dementia subsequently.
- Postoperative delirium may be related to underlying cognitive deficits and may be a consequence or marker of emerging cognitive impairment
- Large study population
- This study used formal cognitive assessment for MCI/dementia where previous studies had not.
- Observational study with potential for confounders and lack of causality.
- Possible biases in study population due to a likely self-selecting group of patients enrolled in MCSA.
- Heterogeneous group of patients with little stratification: all types of surgery were included and all types of anaesthesia were included (unclear what ‘monitored anaesthesia care’ entailed) – difficulty in interpreting the results and/or drawing clinically useful conclusions.
- >50% of surgeries were day cases.
- A median of 8.8 months elapsed from the time of the last cognitive assessment until surgery – some patients with pre-op MCI/dementia not picked up?
- CAM-ICU is not a validated research tool for this patient cohort.
- Overall incidence of POD was low compared with other studies.
- A third of patients were not available for post-operative MCSA follow-up.
- Variation in time to 1st post-op follow-up (median time 9.0 (4.6–12.7) months).
Summary by Dr Tammy Ng