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 applicat ion 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 expose d to isoflurane and the contralateral forearm to water for 30 min. Then, th e response of both forearms to a mechanical stimulus of 650 gr and an elect rical 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 av eraged responses to the mechanical and electrical stimuli obtained from bot h forearms after exposure to isoflurane were expressed on a VAS scale and c ompared 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 mecha nical 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 compa red 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.