PREDICTING LOSS AND EMERGENCE OF CONSCIOUSNESS WITH BISPECTRAL INDEX AND PROPOFOL BLOOD CONCENTRATION DURING PROPOFOL/FENTANYL ANESTHESIA

Abstract

S229 Bispectral index(BIS) has been reported to be a reliable technique to display the depressant level of cerebral cortex. In this study, we observed the BIS values and propofol plasma concentration(Cp) from consciousness to unconsciousness during induction and conversely during recovery as well as when the orientation restored. METHODS: with the approval of our Human Ethical committee and written informed consent, 20 ASA I-II patients (age 18-55 yr) undergoing elective, 1-4 hours surgeries were studied. All patients were unpremedicated for sedation. A radial arterial catheter was inserted to obtain blood samples for subsequent measurement of Cp. EEG parameters(BIS, SEF and MF) were continuously monitored from a bifrontal montage (Fpl-Cz and Fp2-Cz). Anesthesia was induced by propofol (30 mg [center dot] kg-1 [center dot] hr-1) Endotrachael intubation was facilitated by vecuronium. Anesthesia was maintained with fentanyl (2 [micro sign] g[center dot]kg[center dot]hr (-1))injected intermittently and propofol at rate to keep adequate anesthesia until the end of operation. EEG parameters and Cp were measured at following endpoints: loss of consciousness and eyelash reflex; recovery of consciousness, eyelash reflex and orientation during emergence of anesthesia. Consciousness was decided relying on the patient's response to verbal command. Orientation was defined as being able to state his or her name, date of birth, and age. Data were analyzed with Anova and paired t-test, and presented as mean +/- SD. RESULTS: The BIS value at recovery of consciousness was higher than that from consciousness to unconsciousness(P<0.01). Meanwhile, the Cp was required at lower level when consciousness recovered than that when consciousness lost (P<0.01). (Table 1 and Table 2)Table 1: Data during inductionTable 2: Data during recovery of anesthesiaCONCLUSIONS: The recovery of consciousness from propofol anesthesia requires higher BIS level than does unconsciousness during induction. Meanwhile, lower propofol plasma level is necessary. Although as the nonsteady state, the blood concentration may not certainly reflect the level of brain. The Cp required for recovery of consciousness and eyelash reflex is at 2.44-2.48 [micro sign] g[center dot]kg-1, a little higher than that (1.9 [micro sign] g[center dot]ml-1) computed by other authors previously [1]. The orientation can restore with mean BIS 85 with Cp at 1.86 [micro sign] g[center dot]kg-1.