An animal model for surgical anesthesia and analgesia: characterization with isoflurane anesthesia and remifentanil analgesia.

UNLABELLED: With a traditional clamp test alone, quantitative evaluation of the level of surgical anesthesia/analgesia is not easy. We have developed a rabbit model that allows for repeated quantification of the varying level of surgical anesthesia/analgesia using both mechanical and electrical stimulation as simulated surgical stimuli. After tracheostomy and intravascular cannulations under isoflurane anesthesia, eight rabbits were placed on a sling that allowed for free movement of the head and extremities. The inspired isoflurane concentration was reduced from 3% to 1.5% and then to 0%. Remifentanil was then infused at 4 graded infusion rates (0.1-0.8 microg. kg(-1) x min(-1)). At each drug dose, analgesic variables were determined including the number of animals behaviorally unresponsive to clamping the forepaw (nonresponders) and threshold voltage of subcutaneous electrical stimulation (2 Hz, 5 Hz, and 50 Hz) required to evoke the head lift (HLT, pain detection/arousal threshold) and escape movement responses (EMT, pain tolerance threshold). With increasing drug doses, HLTs and EMTs at 5 Hz increased dose-dependently and most proportionately to increases in the number of nonresponders, a standard indicator of the anesthetic/analgesic level. Therefore, using the HLT and EMT at 5 Hz combined with a clamp test, this rabbit model allows for quantitative evaluation of the varying level of surgical anesthesia/analgesia. IMPLICATIONS: We have developed a rabbit model of surgical anesthesia and analgesia using both mechanical and electrical stimulation as simulated surgical stimuli, which allows for repeated, quantitative, and qualitative evaluation of the varying level of surgical anesthesia and analgesia, differentiation between sedative/hypnotic and analgesic components of drug actions, and simultaneous monitoring of all the clinically relevant physiological variables including cardiovascular and respiratory variables.