• Jing-wen Yang, Ming-liang Yi, Yun-fei Chai, Wen-sheng Zhang, and Jin Liu.
• Department of Anesthesiology, West China Hospital, Sichuan University, Chengdu 610041, China.
• Sichuan Da Xue Xue Bao Yi Xue Ban. 2007 Nov 1;38(6):973-6.

ObjectivesTo explore the effect of fentanyl on 50% effective dose (ED50) of emulsified isoflurane for hypnosis and to define the type of interaction between fentanyl and emulsified isoflurane during rat hypnosis.Methods125 male adult Sprague-Dawley rats (240-300 g) were divided into 5 groups depending on the drugs administered via the tail vein. The up-and-down sequential allocation technique was used to determine ED50 of fentanyl in the loss of righting reflex. According to above experiment results, the up-and-down sequential allocation technique was also used to determine ED50 of emulsified isoflurane combined with different fentanyl dose of 7.2 microg/kg (1/4 ED50), 14.3 microg/kg (1/2 ED50) or 21.5 microg/kg (3/4 ED50), respectively, and also without the fentanyl in the loss of righting reflex. Fentanyl was administered intravenously for 20 s followed by emulsified isoflurane for 10 s. The interval between the two was 1.5 min in groups administered with both. ED50 was calculated by using Dixon-Mood method. The isobolographic and algebraic analyses were used to define the type of interaction between fentanyl and emulsified isoflurane.ResultsThe body weight and sex of rats was not significantly different between the 5 groups. ED50 was (28.7 +/- 2.1) microg/kg (26.5-30.8 microg/kg) in the fentanyl group, (0.525 +/- 0.032) mL/kg in the fentanyl 7.2 microg/kg +/- isoflurane group, (0.108 +/- 0.019) mL/kg in the fentanyl 14.3 microg/kg+isoflurane group, (0.075 +/- 0.011) mL/kg in the fentanyl 21.5 microg/kg+isoflurane group and (0.670 +/- 0.054) mL/kg in the isoflurane group. The isobolographic analysis indicated that ED50 of isoflurane decreased progressively in a non-linear fashion in the presence of increasing dose of fentanyl. The isobolographic and algebraic analyses demonstrated that the combination use of fentanyl and emulsified isoflurane could produce a synergistic effect on hypnosis.ConclusionsFentanyl enhances the hypnotic effect induced by emulsified isoflurane. The administration of associating fentanyl with emulsified isoflurane produces a synergistic effect on rat hypnosis.

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