Definition Of A New Index For Depth Of Anesthesia Using EEG Sub

Definition Of A New Index For Depth Of Anesthesia Using EEG Sub-Parameters Combined By Fuzzy Logic.

BE Rodriguez, MSc¹, EW Jensen, PhD^1, P Martinez, MSc¹, H Litvan, MD, PhD¹, MMRF Struys, MD, PhD²

¹Cardiac Anesthesia Research Unit, Hospital Santa Creu I Sant Pau, Barcelona, Spain

²Gent University Hospital, Gent, Belgium

Background and Goal of Study.

The objective of this study was to show that a reliable index for assessing consciousness in anaesthetised patients could be defined using sub-parameters from the EEG as inputs of an adaptive neuro-fuzzy inference system (ANFIS). The advantage of ANFIS is that it does not assume an underlying mathematical function governing the causal relationship between the EEG values and the clinical state of the patient. The performance of the new index, called Cerebral State Index (CSI), was evaluated in a retrospective study.

Materials and Methods.

After Gent Hospital Ethics Committee approval, informed consent was obtained from 20 ASA I female patients (18-60 years), scheduled for ambulatory gynecologic surgery. The data has recently been published in another study1. Propofol infusion was initiated until the patient had no response to noxious stimuli (Observer’s Assessment of Alertness and Sedation scale (OAAS) 0). OAAS level was estimated every 4min. and the effect-site concentration for propofol was calculated using the Schnider model. Four EEG sub-parameters (beta ratio=log(E30-42.5Hz/E11-21Hz), alpha ratio=log(E30-42.5Hz/E6-12Hz), beta – alpha ratio=log(E6-12.5Hz/E11-21Hz) and Burst Suppression) were used to define the inputs to the fuzzy system. The output of the fuzzy system is the CSI.

Results and Discussions. The prediction probability (Pk) between the CSI and OAAS was 0.92. The figure shows the box plot of the CSI versus the OAAS for the data set.

Conclusion.

The results show that in this population depth of anaesthesia can be measured reliably by using a combination of parameters calculated from the frequency content of the EEG.

References.

1.Struys MMRF et al. Anesthesiology 2002; 96:803-16