We agree with Professor Kopp that hyperoxia during surgical anaesthesia might contribute to the higher risk of dementia following anaesthesia and surgery. Growing evidence has demonstrated that oxidative stress may augment the production and aggregation of amyloid-beta and facilitate the phosphorylation of tau. Evidence has suggested that oxidative stress is an important factor contributing to the initiation and progression of Alzheimer’s disease. ^{Reference Zhao and Zhao1} Animal and human studies have also demonstrated increased oxidative stress following anaesthesia and surgery. ^{Reference Lee2,Reference Yalcin, Aydoğan, Yuce, Kucuk, Karahan and Vural3} Furthermore, Kalimeris et al showed that propofol, which has antioxidant effects, seemed to improve cognitive performance after carotid endarterectomy, compared with sevoflurane. ^{Reference Kalimeris, Kouni, Kostopanagiotou, Nomikos, Fragopoulou and Kakisis4} Therefore, oxidative stress after anaesthesia and surgery might contribute to the hazard risk of dementia development. Although the exact mechanism of oxidative stress remains elusive, the perioperative events contributing to oxidative stress include ischaemia-reperfusion damage, surgical trauma, ^{Reference Lee2} and also iatrogenic hyperoxia during anaesthesia, as Professor Kopp elaborated. However, further studies need to be conducted to demonstrate the exact mechanism of oxidative stress due to anaesthesia and surgery in humans, and to demonstrate the effect of antioxidant agents to prevent the potential detrimental effect on cognitive function following anaesthesia and surgery.