Anesthetic Depth Assessed by Processed EEG (pEEG) - a Comparison of Manual Total Intravenous Anesthesia and Target Controlled Anesthesia in Tumor Resection Via Craniotomy

Background The incidence of primary tumors in the central nervous system in adults in Sweden is approximately 1400 per year. Gliomas constitutes the most common form, approximately 50%. The neurosurgery aims at securing material for pathological-anatomical diagnosis, reduction of symptoms, maximal reduction of tumor mass with minimal functional impact. An important feature of neurosurgical anesthesia, apart from intraoperative stability, is early postoperative recovery of consciousness with minimal residual sedation. This is a key factor to enable early neurological assessment and early discovery of postoperative complications (hematomas).

In total intravenous anesthesia the anesthesia drugs (e.g. propofol and remifentanil) are supplied by continuous intravenous infusion. The pumps used for administration can be programmed manually (in mg/kg/h or mcg/kg/min, manual total intravenous anesthesia, mTIVA) or using a programmed algorithm (target controlled infusion, TCI, where the algorithm calculates the concentration of drug at the effect site). Regardless of programing system, the anesthetist or anesthetic nurse adjusts the programming to the patients´ needs during anesthesia and surgery. The Neurosurgical anesthesia section of Lund University Hospital, Lund, Sweden, uses both mTIVA and TCI and all exposed anesthetic personnel are comfortable with both mTIVA and TCI.

Montoring of anesthetic depth is based on physiological reactions. In neurosurgical anaesthesia access to face and pupils are restricted/absent and thus monitoring further restricted. To add to the monitoring of anesthetic depth several processed simplified EEG systems (pEEG) have been developed. EEG systems have proprietary underlying algorithms and are thus not directly comparable. The recommendations regarding adequate anesthesia dept differs considerably numerically. pEEG -systems are expected to add to the evaluation of anesthetic depth, reduce the risk of awareness and reduce the risk of over- anesthetizing with hypotension and prolonged recovery of consciousness during emergence. pEEG has predominantly been assessed in other subspecialities than neuroanesthesia. In neuroanesthesia interference of the pEEG monitoring system with the surgical field is one factor that has to be taken into account when placing the monitoring system, especially in frontally placed tumors.

Bispectal index (BIS, Medtronic,) is one of several commercially processed EEG systems (pEEG). BIS is a pEEG index ranging from 0-100, where 0 corresponds to isoelectric EEG and 100 to full alertness. Recommended anesthesia depth is 40-60 intraoperatively. The EEG-monitoring in the BIS system is available as a unilateral strip increasing clinical usefulness in this setting.

The aim of this study is to improve anaesthesia and monitoring for intracranial tumor resection by evaluating the effect of pEEG monitoring for propofol/remifentanil anesthesia delivered by manual total intravenous anesthesia (mTIVA) or target controlled infusion (TCI).