British journal of anaesthesia
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Minimum alveolar concentration (MAC) and MAC-awake decrease with age. We hypothesised that, in clinical practice, (i) end-tidal MAC fraction in older patients would decline by less than the predicted age-dependent MAC decrease (i.e. older patients would receive relatively excessive anaesthetic concentrations), and (ii) bispectral index (BIS) values would therefore be lower in older patients. ⋯ The age-dependent decline in end-tidal MAC fraction delivered in clinical practice at our institution was less than the age-dependent percentage decrease in MAC and MAC-awake determined from published studies. Despite receiving higher aaMAC fractions, older patients paradoxically showed higher BIS values. This most likely suggests that the BIS algorithm is inaccurate in older adults.