1. Bispectral index at loss of consciousness and in response to laryngoscopy measured on healthy hemispheres during pseudo- steady state propofol and remifentanil anesthesia. Houthoofd J 1,2, Wyler B 2, Kalala JP 3, Struys MMRF 2,4, Vereecke H 4. 1 Department of Anesthesiology, Ghent University Hospital, Ghent, Belgium 2 Department of Anesthesiology, Ghent University, Ghent, Belgium 3 Department of Neurosurgery, Ghent University Hospital, Ghent, Belgium 4 Department of Anesthesiology, University Medical Center Groningen, University of Groningen, the Netherlands Introduction We studied asymmetry between bilateral BIS measurements at loss of consciousness (LOC) and after laryngoscopy measured in healthy adults during a propofol and remifentanil anesthesia. We hypothesized that the dose of remifentanil may affect the magnitude of inter-hemispheric differences. Methods After EC approval and informed consent, 40 cervical and lumbar hernia patients were included. We measured bilateral BIS (VISTA-XP4 with BIS quarto™ sensor). (Covidien,Dublin,Ireland) (Figure 1) Effect- site titration of remifentanil (Ce REMI ) (Minto Model) and propofol (Ce PROP ) (Schnider model, fixed time to peak effect) was administered. All data was captured by RUGLOOPII (Demed, Temse, Belgium). Ce REMI was titrated to either a high (5ng/ml) or low (3ng/ml) dose until steady-state. Ce PROP was started at 2µg/ml and increased stepwise (0.5µg/ml/step) until LOC, defined as a transition from level 3 to 2 on the Modified Observers Assessment of Alertness and Sedation scale. Gentle mask ventilation was performed after LOC with 100% oxygen. After equilibration time, laryngoscopy was performed and a blinded BIS response was measured during 3 minutes. Interhemispherical differences in BIS response larger than 10% were considered clinically relevant. Conclusions Bilateral BIS measurements did not provide more information compared to unilateral BIS. The value of bilateral measurements might be more eminent in diseased brains (tumor) or brains at risk for ischemia (carotic artery surgery). Results No demographic differences were present between high and low Ce REMI groups, except for age (Table 1). Time to LOC and BIS at LOC was not statistically different between groups (Table 2). Ce PROP at laryngoscopy was 3.4 ± 0.7 and 3.7 ± 0.9 (Mean ± SD) for respectively the low and high Ce REMI group. Regardless of Ce REMI, we could not observe interhemispheric BIS responses larger than 10%. BIS at LOC Median BIS one minute before laryngoscopy (baseline) Median BIS one minute after laryngoscopy Delta BIS = BIS response Left hemisphere 3 Ce REMI group 68 ± 1057 ± 959 ± 102 ± 5 5 Ce REMI group 73 ± 857 ± 956 ± 9-1 ± 5 Right hemisphere 3 Ce REMI group 69 ± 956 ± 1060 ± 103 ± 6 5 Ce REMI group 73 ± 1057 ± 1056 ± 9-1 ± 5 Table 1 Table 2 *p<0.05 Demographics Age (years+/- SD) Weight (kg+/-SD) Height (cm+/-SD) Time to LOC (sec+/-SD) 3CeREMI group50 ± 11 *74 ± 16170 ± 9598 ± 124 5CeREMI group43 ± 9 *77 ± 14173 ± 10609 ± 170 Figure 1