Preoperative cognitive impairment predicts deep anaesthesia and higher postoperative pain in elderly patients: an observational study

BACKGROUND: The prevalence of cognitive impairment and its associated risks under general anaesthesia increases with age. This necessitates careful observation and mitigation of anaesthetic risk in elderly patients. While deeper anaesthetic states are hypothesised to predispose patients to postoperative delirium, the causal mechanisms remain unclear, particularly concerning age-related sensitivity to anaesthetics and cognitive deficits. METHODS: This study aimed to investigate the relationship between preoperative cognitive impairment and variability in anaesthetic sensitivity. Additionally, it evaluates the potential of electroencephalogram parameters as markers for identifying cognitive impairment. 84 patients aged ≥ 65 years who underwent elective urological surgery lasting ≥ 60 min were included in this exploratory observational study. Preoperative cognitive function was assessed using the Montreal Cognitive Assessment (MoCA). Cardiovascular and respiratory parameters, anaesthetic concentrations, electroencephalogram indices, and burst suppression ratios were recorded digitally. The primary outcome was the correlation between MoCA scores and deep anaesthesia levels. Secondary outcomes included quantitative electroencephalogram analysis, postoperative pain, and incidence of delirium. RESULTS: Of the 84 patients screened, 67 were included (median age: 70 67 to 74 years; median total procedure time: 200 166 to 247 minutes). The mean MoCA score was 24.3 (± 3.2) points. Cognitive impairment (MoCA score < 26) was identified in 64.2% of the patients. Lower MoCA scores correlated with prolonged periods of deep anaesthesia (ρ=-0.27; P = 0.027). Severe cognitive impairment was associated with longer durations of deep anaesthesia (20.1% vs. 1.1% of the monitoring window; P = 0.006). Burst suppression occurred in 31.3% of the patients but showed no association with MoCA scores. Cognitive impairment was linked to increased postoperative pain requiring treatment (P = 0.001), but not to delirium incidence. CONCLUSIONS: Severe preoperative cognitive impairment was associated with prolonged episodes of deep anaesthesia despite comparable anaesthetic dosages, suggesting heightened sensitivity in these patients. Further studies are needed to determine whether these findings can serve as markers for identifying cognitive impairment in preoperative assessments.