Target-controlled anaesthesia with propofol and remifentanil: loss of the eyelash reflex and evolution of the bispectral index at induction

A. Finianos, P. Hans, E. Coussaert, P.Y. Dewandre, J.F. Brichant, 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

The bispectral index (BIS) has been shown to monitor accurately loss of consciousness during induction of anaesthesia with propofol (PPF) (1). The present study investigated the loss of the eyelash reflex and the BIS during induction of anaesthesia with target-controlled infusions of PPF and remifentanil (REM).

Methods

After Ethics Committee approval and informed consent were obtained, 28 ASA I or II patients undergoing elective surgery were studied. Premedication consisted in alprazolam 1 mg given orally 1 h before surgery. Patients were randomly allocated to 4 groups of 7 patients each, according to the REM target effect-site concentration (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. During induction of anaesthesia, BIS (Aspect Medical System A-1000) was recorded in all patients and the loss of the eyelash reflex was noted. The PPF Ce-BIS curve was calculated. Univariate analysis of variance was applied to the time elapsed between the beginning of PPF infusion and the loss of the eyelash reflex (T eye), the PPF Ce corresponding to the loss of the eyelash (PPF Ce eye), the lowest BIS value observed during PPF infusion (LBIS), the PPF Ce corresponding to LBIS (PPF Ce LBIS), the PPF Ce₅₀ (PPF concentration producing 50% of BIS effect), and the steepness (g) of the PPF Ce-BIS curves. P < 0.05 was considered statistically significant.

Results

Patients characteristics and BIS values before PPF infusion were similar in all groups. Values (mean ± SD) of T eye (sec), PPF Ce eye (µg ml^-1), LBIS, PPF Ce LBIS (µg ml^-1), PPF Ce₅₀ (µg ml^-1) and g are displayed in table 1. The eyelash reflex disappeared at low PPF Ce. The PPF Ce LBIS was lower than the target PPF Ce (global value : 2.63 ± 0.4 µg ml^-1). ANOVA did not show any significant difference between groups in the above parameters.

	T eye	PPF Ce eye	LBIS	PPF Ce LBIS	PPF EC50	g
G1	77.6±17.8	1.30±0.5	28.6±4.6	2.69±0.6	2.00±0.4	7..5±5.3
G2	66.7±16.0	1.07±0.5	30.7±7.9	2.66±0.3	2.01±0.3	7.9±9.6
G3	55.7±19.5	0.85±0.5	36.5±11.4	2.61±0.6	1.99±0.4	7.1±3.0
G4	62.1±17.8	1.01±0.4	36.9±8.6	2.54±0.4	2.00±0.2	8.8±4.0

Conclusions

At induction of anaesthesia, the loss of the eyelash reflex was observed at low PPF Ce. The lowest BIS values were recorded at PPF Ce lower than 3 µg ml^-1. The loss of the eyelash reflex and the PPF Ce-BIS relationship were not affected by the REM target Ce.

References

1. Struys et al, Acta Anaesthesiol Scand 1998; 42: 628-36