Perioperative Electroencephalography Characteristics of Postoperative Delirium in Elderly

The investigators aim to identify preoperative Electroencephalogram (EEG) markers indicating patients at risk to develop postoperative delirium (POD), so that the anesthetist may adjust medications and dosages in order to avoid POD. Second, the investigators aim to specify intraoperative EEG signatures and EEG states that are related to POD and long-term cognitive dysfunction, again to enable physicians to adapt their procedure. Third, the investigators aim to identify EEG signatures during stay in the recovery room that is directly related to POD, and may therefore be used as diagnostic tool, as well as a predictor for the development of long-term cognitive deficits (POCD).

The investigators conduct this observational study to identify pre-, intra- and postoperative Electroencephalogram (EEG) signatures / intraoperative EEG states related to postoperative delirium (POD) and postoperative cognitive deficit (POCD) in elderly patients \> 70 years. This includes the following tasks at five different time-points

1. Pre-operative frontal EEG recording during anesthesia evaluation one day before surgery / anesthesia to develop an EEG marker to predict the development of POD. This includes the stratification of EEG data related to age, gender, and pre-operative cognitive function. Pre-operative POCD assessment (CANTAB connect, word pair recognition test, Mini Mental State Test, and Trail Making Test A and B) to classify cognitive capacity of each patient before start of anesthesia.
2. Intra-operative frontal EEG recording from start of anesthesia procedure until discharge to the recovery room to identify EEG signatures / EEG states to predict the development of POD / POCD. This includes the stratification of EEG data related to age, gender, pre-medication, anesthetics, and analgesics used during anesthesia procedure.
3. Post-operative frontal EEG recording during the recovery room stay to develop an EEG marker / identify EEG signatures to diagnose POD and predict POCD. This includes the stratification of EEG data related to age, gender, anesthesia procedure, and analgesics administered during the recovery room stay. POD will be assessed during stay in the recovery room by the NuDesc Score and DSM V criteria.
4. Follow-up POD assessments until the 5th postoperative day, where the patient will be visited twice daily (8a.m.-10a.m. and 5p.m.-7p.m.) and assessed via DSM V / NuDesc criteria on the peripheral ward, or via Confusion Assessment Method for intensive Care Unit (CAM-ICU) criteria during an intensive care unit stay.
5. Follow-up POCD assessments one day before and 3 months after surgery, where the patient will undergo a \~1 hour cognitive testing with the CANTAB connect.

Eligibility Criteria:
Inclusion Criteria:

* Patients aged \>70 years
* Planned operation time \>1 hour
* Expected hospital treatment period of 5 days,
* Anesthesia induction, anesthesia maintenance with either Propofol or an inhalative anesthetic agent as Sevoflurane or Desflurane,
* The ability to give informed consent

Exclusion Criteria:

* Patients with a history of neurological or psychiatric disorders
* Known carotid artery Stenosis
* Obstructive sleep apnea Syndrome
* Planned neurosurgery
* Current medication of tranquilizers / antidepressants
* Isolation of patients with multi-resistant Bacteria
* Inability of the patients to speak and/or read German
* Homelessness or other circumstances where the patient would not be reachable by phone or postal services during follow-up
* Intraoperative EEG data file analysis will be excluded ex post,

  1. when intraoperative use of any other anesthetic agent for induction as Propofol occurred or
  2. by use of any other anesthetic agent for anesthesia maintenance other than Propofol or volatile anesthetics as Sevoflurane or Desflurane or
  3. when anesthesia agents as Ketamine, Nitrous oxide, Etomidate or Dexmedetomidine were given or
  4. if body temperature drops below 34° or rises above 38° during surgery