A rabbit model for evaluation of surgical anesthesia and analgesia: characterization and validation with isoflurane anesthesia and fentanyl analgesia

• Published in: Journal of anesthesia 2004-11, Vol.18 (4), p.282-291
• Main Authors: Hayashida, Masakazu, Fukunaga, Atsuo, Fukuda, Ken-Ichi, Yamazaki, Shin-Ya, Arita, Hideko, Hanaoka, Kazuo
• Format: Article
• Language: English
• Subjects: Analgesia; Analgesics, Opioid; Anesthesia; Anesthetics, Inhalation; Animals; Disease Models, Animal; Fentanyl; Isoflurane; Male; Rabbits; Surgical Procedures, Operative
• ISSN: 0913-8668; 1438-8359
• DOI: 10.1007/s00540-004-0254-4

With a clamp test, quantitative estimation of the level of surgical anesthesia/analgesia is not easy. We have developed a rabbit pain model allowing for quantitative evaluation of the level of surgical anesthesia/analgesia using both electrical and mechanical stimuli as simulated surgical stimuli. We evaluated whether this model allows for accurate tracing of dynamically changing levels of surgical anesthesia/analgesia induced by isoflurane and fentanyl. Eight rabbits tracheotomized and vascularly cannulated under 3% isoflurane anesthesia were placed on a sling that allowed for free movement of the head and extremities. After the isoflurane concentration was reduced stepwise to 1.5% and then to 0%, four graded doses of fentanyl (5, 10, 20, and 40 microg.kg(-1)) were injected intravenously at intervals of 120 min. At each dose, anesthetic/analgesic end-point variables were determined, including the number of animals behaviorally unresponsive to clamping the forepaw (nonresponders) and the threshold voltage of subcutaneous electrical stimulation (2, 5, and 50 Hz) required to evoke the head lift (HLT: pain detection/arousal threshold: sedative/hypnotic index) and the escape movement (EMT: pain tolerance threshold: analgesic index). With increasing doses of isoflurane and fentayl, HLTs and EMTs, especially those at 5 Hz, increased dose-dependently and proportionately to increases in the number of nonresponders to clamping the forepaw, a standard indicator of the anesthetic/analgesic level. Using the HLT and EMT, especially at 5 Hz, combined with a clamp test, this rabbit model allows for repeated, quantitative, and distinctive evaluation of the dynamically changing levels of both sedative/hypnotic and analgesic components of surgical anesthesia/analgesia.