Is there an association between post-op delirium and cognitive decline?

Postoperative delirium in elderly patients is associated with subsequent cognitive impairment Sprung et al. British Journal of Anaesthesia, 119 (2): 316–23 (2017)

“I’m most afraid of losing my mind. You lose your identity, your sense of who you are, where you are.” – Stephen King

Background

  • 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.

Objectives

  • 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.

Hypothesis

  • Surgical patients who are cognitively normal, who develop POD are at increased risk for subsequent development of MCI or dementia.

Study Population

  • 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.

Methods

  • 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.

Results

  • 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].

Author’s Conclusions

  • 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

Strengths

  • Large study population
  • This study used formal cognitive assessment for MCI/dementia where previous studies had not.

 Limitations

  • 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

 

 

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