Remifentanil does not affect the bispectral index nor the relationship between propofol and the bispectral index at induction of anaesthesia

A. Finianos, P. Hans, E. Coussaert, J.F. Brichant, P.Y. Dewandre, F. Cantraine, M. Lamy. University Department of Anaesthesia & Intensive Care Medicine, CHR de la Citadelle, CHU Liege, 4000 Liege, Department of Computer Science, Free University of Brussels, 1070 Brussels, Belgium

Background and goal of the study

Opioids are known to interact with propofol (PPF) concentration that assures adequate anaesthesia and return of consciousness (1). This study aimed to investigate the effect of remifentanil (REM) on the bispectral index (BIS) and on the relationship between the PPF effect-site concentration (Ce) and the BIS at induction of anaesthesia.

Methods

After Ethics Committee approval and informed consent, 28 ASA I or II patients undergoing elective surgery were included in the study. Premedication consisted in alprazolam 1 mg given orally 1 h before surgery. Anaesthesia was induced with REM and PPF using a target-controlled infusion device. Patients were randomly allocated to 4 groups of 7 patients each, according to the REM target Ce (G₁:2 ; G₂:4 ; G₃: 6 ; G₄: 8 ng ml^-1). Once the REM Ce was reached, PPF was infused to achieve a 3 µg ml^-1 Ce. Bis (Aspect Medical System A-1000) was recorded before induction (T₁), once the REM target Ce was achieved (T₂) and during the PPF infusion. Univariate analysis of variance was applied to the difference in BIS values between T₁ and T₂ (DBIS T₁-T₂), to the lowest BIS (LBIS) values recorded during PPF infusion, and to the difference in BIS values between T₂ and LBIS (DBIS T₂-LBIS). P < 0.05 was considered statistically significant.

Results

Patients characteristics and baseline BIS values (T1) were similar in all groups. BIS values at T₁ and T₂, and lowest BIS values during PPF infusion are shown in table 1 (means ± SD). ANOVA applied to the parameters mentioned above did not show any significant difference between groups.

Group	BIS at T1	BIS at T2	DBIS T1-T2	L BIS	DBIS T2-LBIS
G1	93.4±4.7	95.3±4.6	-1.04±1.4	28.6±4.6	66.64±3.3
G2	93.8±5.9	93.8±7.7	0.03±3.3	30.7±7.9	63.10±10.7
G3	96.1±2.5	93.8±4.5	2.00±5.7	36.5±11.4	57.26±12.2
G4	96.3±2.7	96.3±1.9	0.00±1.1	36.9±8.6	59.49±9.8

Conclusions

REM target Ce from 2-8 ng ml^-1 did not affect BIS nor the relationship between PPF Ce and BIS during PPF infusion up to a target Ce of 3 µg ml^-1. In these conditions, BIS measured only the hypnotic effect of PPF.

Reference

1. Vuyk et al., Anesthesiology 1997; 87: 1549-62