CVI BIS study.

Anesthesia has made enormous progress in the last couple of decades making surgery a reliable and safe procedure with minimal morbidity and mortality. Despite the progress many aspects of anesthesia remain elusive. Two important items that have recently been the focus of attention are the measurement of the depth of anesthesia and the measurement of nociception (or ‘pain-related afferent input’) during anesthesia. The current study will focus on the latter of these two items: measurement of nociception during anesthesia. In order to get an indication of nociception we will make use of a recently developed index from the frontal EEG and EMG, the Composite Variability Index (CVI) by Aspect medical Systems. The CVI is based on the observations that the EEG-related variable BIS (bispectral index) rapidly responds to painful surgical stimuli during anesthesia and that the BIS waveform and EMG are more variable in case of a low analgesic load. This indicates that when insufficient amounts of analgesics have been infused the BIS response (ie increase) to a surgical stimulus will be larger but also that the BIS and EMG display increased variability.



The CVI is based on the standard deviation of BIS and EMG (sBIS and sEMG). It combines sBIS and sEMG into a single measure of variability ranging from 0 to 100. Preliminary data suggest a possible predictive effect of the initial change in CVI just prior to a patient movement.



In the current study we will measure CVI in ASA 1-3 patients during elective abdominal surgery under fentanyl/sevoflurane/epidural anesthesia. We will monitor patient movement as primary correlate to CVI and cardiovascular parameters as secondary correlates (eg, cardiac output, pulse transit time, blood pressure and heart rate).

When insufficient amounts of analgesics have been infused during anestesia, the BIS response a surgical stimulus will be larger and the BIS and EMG display increased variability (CVI).

From start of induction until end of surgery.

Sixty ASA I-III patients for elective abdominal surgery will be given an epidural catheter prior to induction. After placement of the catheter, anesthesia will be started either with the epidural anesthesia/sevoflurane + fentanyl in a high dose (7mcg/kg) or with a low (2mcg/kg) dose. No muscle relaxation will be used for intubation. Anesthesia will be maintained with sevoflurane and fentanyl bolus 2-3mcg/kg (high dose) vs 0,5-1mcg/kg (low dose) as judged by the attending anesthesiologist.