Background: The loss of cholinergic neurones in the basal forebrain has been shown to correlate to the extent of cognitive dysfunction during ageing in humans and to the hypnotic potency of propofol in animal models. We examined how the preoperative cognitive status, as assessed by mini-mental state examination (MMSE), may interact with propofol consumption during anaesthesia in the elderly.
Methods: In a prospective study, we recruited 41 patients (65-99 yr) undergoing surgery for hip fracture. Femoral nerve block was performed for analgesia. Target-controlled infusion of propofol (Schnider's model) was adjusted to the bispectral index within the range 40-60. Multiple linear regression analysis determined whether age, BMI, gender, duration of anaesthesia, and preoperative MMSE score affected the propofol consumption (general linear model, Systat 8.0).
Results: BMI and MMSE score significantly affected the mean value of propofol consumption. A low MMSE score (below 19) was associated with an observed decrease in propofol requirement in patients >65 yr of age. No significant effect of age, gender, and duration of anaesthesia on the propofol consumption was observed.
Conclusions: Propofol requirement to maintain hypnosis during general anaesthesia appears to decrease with deterioration in the cognitive status in the elderly. We suggest that a cognitive dysfunction linked to a cerebral cholinergic dysfunction may influence the brain sensitivity for propofol in aged patients.