Skin application of isoflurane attenuates the responses to a mechanical and an electrical stimulation

Purpose: This prospective randomized crossover study was performed to test the potential of an analgesic effect of isoflurane after its local application to the skin. Methods: We evaluated the local analgesic effect of isoflurane solution in 31 healthy volunteers. The right or left forearm of each subject was exposed to isoflurane and the contralateral forearm to water for 30 min. Then, the response of both forearms to a mechanical stimulus of 650 gr and an electrical stimulus of 2 Hz was tested. The procedure was repeated the next day with the forearms exposed to anaesthetic or water in an inverse way. The averaged responses to the mechanical and electrical stimuli obtained from both forearms after exposure to isoflurane were expressed on a VAS scale and compared with the averaged responses obtained after exposure to water, using the Wilcoxon signed-ranks matched-pairs test. Results: The average VAS scores obtained from both forearms after the mechanical stimulus were decreased after isoflurane compared with water (3.5 +/- 2.1 cm vs 4.3 +/- 2.2 cm, P < 0.0001), After the electrical stimulus local application of isoflurane was associated with a decrease in the VAS scores obtained from both the right and left forearms (3.6 +/- 2.0 cm) when compared with water, (5.2 +/- 2. 1 cm, P < 0.0001). Conclusion: These data suggest that isoflurane may have an analgesic effect in the peripheral tissues, which may interfere with the MAC determination as well with decreased responses to other nociceptive stimuli.