In the perioperative period, severe changes can be observed in the endocrine, immune, and nervous system. These changes are called the surgical stress response. Clinically, this can be observed as increased pain response and disturbances in the circadian rhythm, memory, cognitive and executive functions, and may lead to post-operative delirium. The post-operative cognitive dysfunction is associated with increased mortality and risk of prematurely leaving occupation. Post-operative delirium with fluctuating levels of attention and consciousness is a serious condition associated with poor outcome, including longer hospitalisation and increased early mortality.
General anaesthesia may contribute to the surgical stress response. Some data indicate that general anaesthesia per se can cause alterations and disturbances in the brain such as sleep and circadian disturbances. Recent evidence suggests that anaesthetic agents may impair neurogenesis and cause memory impairment. In addition, inhalation anaesthesia may result in more cerebral disturbances compared to total intravenous anaesthesia (TIVA). In this study, we will isolate the effects of the two primary hypnotic agents used in general anaesthesia, sevoflurane and propofol, without the interactions and confounders of polypharmacy and varying levels of disease among a surgical population.
The study consists of two study sessions. In each study session magnetic resonance imaging (MRI) scans will be obtained before and after general anaesthesia, and in addition after one and eight days.
The following imaging modalities will be employed: (i) T1-weighted 3D anatomy (T1w3D), (ii) Diffusion Tensor Imaging (DTI), (iii) resting state functional MRI (rsfMRI). The MRI scans will be supplemented with cognitive testing, sleep evaluation and blood sampling. Thus, the set-up for each volunteer will be:
Day 0: MRI 1, cognitive testing, questionnaires, and blood sampling. General anaesthesia (maintenance phase with sevoflurane OR propofol according to randomisation), and post-anaesthesia care. MRI 2 and repeated cognitive testing, questionnaires, and blood sampling.
Day +1: MRI 3, cognitive testing, questionnaires, and blood sampling.
Day +8: MRI 4, cognitive testing, and questionnaires.
Session two: Identical to session one, except the volunteer will receive the remaining type of general anaesthesia (sevoflurane or propofol, opposite to session one).
Data evaluation will be conducted with assessor blinded to anaesthesia type.