EEG-based Depth of Anesthesia-monitoring, Effects on Dosage and Cognition

EEG-based Depth of Anesthesia-monitoring During General Anesthesia - Effects on Time to Wake-up and Post-operative Cognition

Depth of anesthesia-monitoring based on EEG changes demands knowledge about the effects of the different anesthetic medications on EEG waveforms. The investigators want to investigate the use of the raw-EEG waveform in addition to indexes (BIS) and EEG spectrogram analyses for depth of anesthesia monitoring. The investigators hypothesize that with the use of this monitoring, anaesthesia providers will be able to better individualize the dosage of anesthetic drugs, and that this will reduce the total consumption of anesthetic medication , thus reducing time to wake-up after surgery. Some studies have indicated that too deep anesthesia, confirmed by "burst-suppression" or isoelectric-EEG , is associated with increased postoperative cognitive dysfunction (POCD). The investigators will therefore assess the patients with the Cambridge Neuropsychological Test Automated Battery tests in mild cognitive impairment (CANTAB-MCI) cognitive function assessment tool.

It has been over 80 years since Gibbs et al showed how the electroencephalogram (EEG) systematically changed in concurrence with increasing doses of hypnotic drugs such as penthobarbital and Ether. The study concluded that "Electroencephalography may therefore be of value in controlling depth of anesthesia and sedation". In spite of a solid documentation of the systematic connection between dosing of anesthetic drugs, EEG-patterns and level of sedation/anesthesia , EEG-based DoA has not become a part of standard of care in anesthetic management. There is abundant evidence of how different anesthetic drugs leads to characteristic fluctuations in human brain electrical activity, relating to depth of anesthesia, anesthetic drug of choice, and age . These anesthetic induced fluctuations are readily visible as changes in the patients EEG. Anesthetic drugs are usually administered in pharmacological models based on a population taking into account their age, weight and height. However, there is a significant difference in how patients respond to these models. In adults there is evidence that the doses needed to achieve consciousness varies with a factor of 2 above and below suggested doses. In under-dosing of anesthetics there is a risk of peroperative awareness . On the other hand there is also evidence that overdosing of anesthetics has harmful effects; children receiving more than 4% Sevoflurane can demonstrate epileptiform activity , and adults overdosing into "burst suppression" during anesthesia has a higher risk of postoperative delirium (POD) and increased occurrence of postoperative cognitive dysfunction (POCD) . Bispectral Index (BIS) is an algorithm developed by Aspect Medical Systems in 1994, which is based on weighted sums of EEG subparameters to present an index from 0 to 100 for depth of anesthesia, where 100 is wide awake, and 0 is an isoelectric EEG. The BIS target for a deep enough anesthesia is set to be between 40 and 60. The BIS number is often in concurrence with other clinical observations related to anesthetic depth, however there is also an experience of divergence. BIS and other EEG-based indices are programmed from adult cohorts, and cannot be directly trusted in children, or the elderly . There is also an incapability in these preprogrammed indices (BIS and other) to integrate how specific anesthetic drugs affect the EEG, and thenceforth the BIS value. An example of this is how the drug Ketamine induces a specific gamma-frequency in the EEG, which the BIS-index translate as a lighter anesthesia, even though the drug is administered "on top of" an already deep level of anesthesia.

Two groups with 50 participants in each group. We want to compare one group with visible EEG-monitor with a group where the EEG monitor is invisible to the anesthetic team.

Patient is blinded to intervention. Outcome assessoring done by patient/IPAD-solution from CANTAB, patient status assessed by blinded care-provider (nurse)

Individual dosing of anesthetic medications based on EEG AND other standardized clinical observations (BP, HR)

raw-EEG and spectrographic EEG-visualization based on the Medtronic Device "Bilateral BiSpectral Index"

Baseline assessment 1 day preoperatively, assessment 2-3 hours after wake-up, and 24 hours after wake-up using CANTAB-MCI

Inclusion Criteria . Participants are eligible to be included in the study only if all of the following criteria apply: Age Participant must be above the age of 18 years , at the time of signing the informed consent. Sex Male and/or female Informed Consent Capable of giving signed informed consent as described in protocol which includes compliance with the requirements and restrictions listed in the informed consent form (ICF) and in the protocol Exclusion Criteria Participants are excluded from the study if any of the following criteria apply: Psychiatric disorders Pregnancy Breast feeding Using antiepileptic drugs. Central neurological disease Unable to complete baseline CANTAB-test.

Data storage and management will follow GCP and GDPR requirements. Data sharing after end of study will follow the current data sharing policy at Oslo University Hospital. Data set can be made available for journal peer review process.

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