Abstract SNACC-52

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Burst Suppression MAC (MACBS) of Sevoflurane is Not Decreased by Remifentanil

1Senpolat S, 1Kruschinski Y, 2Jordan D, 2Kochs E, 3Schneider G
1Helios Klinikum Wuppertal, Wuppertal, , Germany; 2Klinikum rechts der Isar, Technische Universität München, München, Bavaria, Germany germany; 3Helios Klinikum Wuppertal, Witten-Herdecke University, Wuppertal, , Germany

Introduction: The MAC value of a volatile anesthetic is based on movement reactions and may mainly reflect effects on the spinal cord. Therefore, EEG burst suppression MAC (MACBS)has recently been suggested as a measure of anesthetic effects on the brain[1]. The present study was performed to evaluate the influence of different doses of remifentanil (R) on MACBS of sevoflurane (Sevo).

Methods and analysis: After approval from the ethics committee and informed written consent, unpremedicated patients were randomly assigned to receive one of five infusion rates of R (R0 = control group, 0µg/kg/min; R05=0.05µg/kg/min; R1=0.1µg/kg/min; R2=0.2µg/kg/min; R4=0.4µg/kg/min). MACBS was determined using Dixon's “Up and Down” method: with Sevo mask induction, patients received a pre-determined concentration of Sevo. If burst suppression occurred after a 15 min equiliration, Sevo concentration of the next patient in this group was reduced by 10%. If the EEG did not show burst suppression, Sevo concentration of the next patient was increased by 10%. In each group, measurements were performed until six independent crossover pairs (i.e. two subsequent patients with and without EEG burst suppression) occurred. MAC values in each group were calculated using logistic regression.

Results: MACBS of Sevo was 2.98. In R groups, MACBS was increased (R05: 4.25, R1: 3.81, R2: 4.39, and R4: 4.52).

Discussion: Reduction of MAC (skin incision) by R may mainly reflect spinal and peripheral effects, while MACBS is not reduced by R. In contrast to expectations, there was no synergistic effect of R on MACBS. The increase of MACBS by R may be due to a reduction of external input, reduction of excitatory effects of sevoflurane, or an increased resistance against state transitions.

References: 1. Pilge S. et al.: Brit J Anaesth 2014 (epub ahead of print)

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