Reduction of Intraoperative EEG Burst Suppression (BsR)

Burst suppression (BS) is a not physiological pattern in the electroencephalogram (EEG). BS during general anesthesia is mainly seen as a sign for too deep hypnosis and may increase the risk of postoperative delirium (POD), a disturbance of consciousness arising within 24 hours after surgery. This monocentric, simple masked randomized study aims primarily to investigate, whether particular anesthesiological interventions reduce the occurrence of intraoperative burst suppression. The investigator initiated trial includes 66 patients (male and female) aged ≥ 60 years in two groups (intervention and control group). Secondary aims will be the correlation of burst suppression and mean arterial pressure, concentration of anesthetics and postoperative delirium.

Intraoperative burst suppression represents a non physiological EEG pattern. According to the literature and scientific knowledge, intraoperative burst suppression patterns might be caused either by hypotension resulting in a reduced cerebral circulation or by an oversedation of anesthetics correlating with a very deep level of hypnosis. Some publications exist that discuss the occurrence of intraoperative burst suppression especially in elderly people (aged ≥ 60 years) as a predictor of postoperative delirium and postoperative cognitive dysfunction. None of the studies however was able to prove a causal relationship between burst suppression and postoperative delirium. Contrary it might simply be an epiphenomenon. Conducting this interventional trail primarily aims to prove whether specific anesthesiological interventions, such as the treatment of intraoperative hypotension in first line and/or the reduction of the concentration of anesthetics in second line, reduce intraoperative burst suppression. Hence it might be possible to investigate a possible casualty between burst suppression and postoperative delirium in a second trial.

Intraoperative EEG based monitoring, Level of hypnosis, Burst suppression, Postoperative delirium, EEG-signal characteristics, Entropy

Single masked. The entropy and EEG module will be masked for the responsible anesthetist as well as the study team during the entire investigation.

EEG and Entropy will be blinded. The anesthesiological management will be performed by the anesthetist according to clinical standard operations.

EEG and Entropy will be unblinded. The intervention starts with the start of a positive burst suppression rate. In the case of a concurrent hypotension the anesthetist treats the hypotension according to clinical standard operations in the first step. Hypotension means blood pressure values blow the baseline value which is defined by the lowest, preoperatively measured value. If after this treatment and a reevaluation of the BSR, BSR remains positive, the anesthetist is going to reduce the concentration of anesthetics in a second step. In case of positive BSR and a blood pressure value ≥ the baseline value, the concentration of anesthetics will be reduced as a first measure. The aim is to figure out whether one or both of these interventions can reduce to total, cumulative BSR.

The treatment of hypotension can be done by the responsible anesthetist according to the clinical standard operations including any accepted drug typically used in this hospital. The reduction of anesthetics can be done either by reducing the volatile end tidal anesthetics concentration (ETAC) or the infusion rate of propofol.

The total, cumulative burst suppression rate (BSR) corresponds to area under the curve and is defined by the BSR (%) and the absolute duration of BSR (t).

Evaluation of specific EEG frequencies differentiating BSR caused by hypotension or oversedation of anesthetics.

Screening of the patients regarding a postoperative delirium by a brief confession assessment method (bCAM).

Inclusion Criteria: Age ≥ 60 years Surgical interventions in general anesthesia (volatile or total intravenous anesthesia) expected surgery duration ≥ 1h American Society of Anesthesiologists (ASA) 1-4 written informed consent prior to study participation Exclusion Criteria: Neurological or psychiatric disorders hearing difficulty deafness neurosurgical (intra)cranial surgery pregnancy expected continuous mandatory ventilation after surgery

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Georgii MT, Kreuzer M, Fleischmann A, Schuessler J, Schneider G, Pilge S. Targeted Interventions to Increase Blood Pressure and Decrease Anaesthetic Concentrations Reduce Intraoperative Burst Suppression: A Randomised, Interventional Clinical Trial. Front Syst Neurosci. 2022 Mar 4;16:786816. doi: 10.3389/fnsys.2022.786816. eCollection 2022.