Movement response to skin incision: analgesia vs. EEG parameters

H. Singh, T. Sakai, A. Matsuki. Dept. of Anaesthesiology, University of Hirosaki School of Medicine, Japan

 

Background and Goal of Study

Responses to various noxious stimuli have been studied to monitor the depth of anaesthesia. The bispectral index (BIS) and 95% spectral edge frequency (SEF) have been studied to monitor the hypnotic effect of intravenous (i.v.) anaesthetics (1). Fentanyl supplementation of propofol inhibits the response to skin incision (SI) at lower propofol concentrations (2). This study determined the effect of varying doses of fentanyl with propofol on movement response to SI and BIS and 95% SEF values.

 

Materials and Methods

Following Ethics Committee approval, 68 ASA 1-2 patients, 18-65 yr., were recruited to participate in this study. Patients were administered fentanyl bolus, 0, 1, 2 or 3 mg.kg^-1 i.v. (Groups C, F1, F2 or F3, respectively), 5-min prior to induction of anaesthesia with propofol infusion, 1 mg.kg^-1.min^-1 for 2-min. Patients were intubated with succinylcholine, 1 mg.kg^-1 i.v. and anaesthesia was maintained with propofol infusion, 200 mg.kg^-1.min^-1 until SI. Besides routine monitoring, BIS and 95%SEF were monitored and recorded at baseline (prior to fentanyl bolus) and at SI with A1050 EEG monitor (Rev. 1.21, BIS algorithm 3.3, Aspect Medical Systems, Natick, USA). Movement response to SI and total doses of propofol up to SI were noted. Sustained tetanus was confirmed in all patients prior to SI. Data were analyzed using unpaired t-test, multiple ANOVA and Chi-square test.

 

Results and Discussion

The four treatment groups were comparable with respect to demographic data and lengths of SI. The induction-SI durations were 29.2±7.4, 27.1±6.8, 26.3±7 and 30.1±7.7 min and doses of propofol were 454.1±142, 441.6±118.2, 424.7±100.9 and 435.6±116.8 mg, in the C, F1, F2 and F3 groups, respectively. Fentanyl boluses, 2 or 3 mg.kg^-1 i.v., significantly decreased the number of patients responding to SI without affecting the BIS or 95% SEF values (Table). There were no differences in the BIS or 95% SEF values in four treatment groups. The hypnotic effect of propofol with fentanyl resulted in lower BIS and 95% SEF values at SI. The hypnotic interaction between propofol and fentanyl, 1-3 mg i.v., was not significant to lower the BIS or 95% SEF values.

 

Treat. Group	BIS Baseline	BIS SI	95%SEF Baseline	95% SEF SI	MR
C (n=17)	96.6±1.3	36.6±11.6	19.3±5.6	16±2.8	12
F1(n=17)	96.5±1.3	32.4±9.3	17.9±5.9	14.6±2.6	10
F2(n=17)	97.3±0.4	35±8.8	18.7±4.8	14.7±3.1	4*
F3(n=17)	96.7±1	34.8±9.4	20.1±4.9	15.9±1.4	4*

* P < 0.05(F2 & F3 vs. C);MR: Movement Response

 

Conclusions

Though deeper levels of hypnosis to lower the BIS and 95% SEF values may be effective for preventing the movement response to SI, provision of adequate analgesia rather than maintaining the clinical ranges of the BIS and 95% SEF values may be more reliable for preventing the response to SI as BIS  and 95% SEF measure the hypnotic component of the anaesthetic effect. 

 

References

1. Clin Pharmacol Therap 1997;61:45-58.                 

2. Anesthesiology 1994;81:820-828.