Age‐adjusted minimum alveolar concentration and standards of monitoring

We read with interest the recent multidisciplinary guidelines on the peri-operative care of people with dementia 1. This review discusses the management of patients with pre-existing dementia and those at risk of postoperative cognitive decline (POCD). The international team of renowned authors have carefully examined the available evidence and we support their sensible and workable recommendations. The guidelines highlight that age is a risk factor in making patients more sensitive to both the hypnotic and cardiovascular effects of general anaesthesia 2 and that delivery of excessive doses of anaesthetic agents can affect a person's cognitive trajectory 3. Thus, the authors recommend that there is a requirement to measure the depth of anaesthesia using age-adjusted minimum alveolar concentration (MAC) or minimum inhibitory concentration, and/or processed electroencephalogram (EEG) (bispectral index/entropy). The concept of giving an age-adjusted dose of anaesthetic agents is also promoted in the recently published Association of Anaesthetists’ total intravenous anaesthesia guidelines 4 and the International Fragility Fracture Network Delphi consensus statement on the principles of anaesthesia for patients with hip fracture 5. However, the use of processed EEG-guided anaesthetic administration in preventing cognitive decline is controversial. A recently published randomised clinical trial, that included 1232 patients aged 60 years or older undergoing major surgery, did not reveal a statistically significant difference between the occurrence of postoperative delirium in the processed EEG-guided anaesthetic group compared with a group receiving usual care 6. These findings question the use of processed EEG-guided anaesthesia in preventing POCD. Therefore, the most effective method of delivering age-adjusted anaesthesia if volatile agents are used is with the use of the age-adjusted MAC. Current Association of Anaesthetists’ guidance suggests that monitoring inspired and exhaled volatile anaesthetic agent is required as a minimum standard of monitoring, however, there is no recommendation of an age-adjusted level of anaesthesia. In light of new Association of Anaesthetists’ guidance, which attaches significant importance to administering age-adjusted doses of anaesthesia in order to mitigate postoperative cognitive decline, we strongly believe that the Association of Anaesthetists’ ‘Recommendations for standards of monitoring during anaesthesia and recovery’ must be updated to reflect this. Considering that some modern monitors such as FukudaTM do not come with age-adjusted MAC, we urge the Association of Anaesthetists to update their monitoring guidelines in order to promote patient safety and to ensure consistency across the suite.