Application of Dixon's Up-and-Down Design to Estimate the Minimum Alveolar Concentration of Sevoflurane in Rats with Refined Movement Classification.

When using volatile anesthetic agents, the standard measure of potency is the minimum alveolar concentration (MAC), defined as the alveolar concentration at which 50% of subjects do not show a motor response to a painful stimulus. In clinical and experimental studies, the current consensus states that only "gross purposeful movements" count as a positive motor response and can, therefore, indicate too mild sedation. However, the appropriate level of anesthesia, in both humans and animals, varies individually based on various influencing factors, such as other medications administered. Two animal studies in rats were conducted to examine the effects of tetrahydrocannabinol and ethanol on sevoflurane, one of the most commonly used volatile anesthetics. To estimate the MAC, Dixon's Up-and-Down Design was employed. For the first animal, a predetermined dose of sevoflurane was chosen. After an equilibration period of 15 min, a standardized pain stimulus was applied to the distal third of the rat's tail using a surgical clamp. The animal's response to the stimulus was documented as positive or negative. If a positive motor reaction occurred, the dose for the next animal was increased. Conversely, if the rat did not exhibit a motor response, the dose for the following animal was decreased. Isotonic regression and the bootstrap method were used to estimate the MAC and 95% confidence intervals. This article outlines a detailed protocol for assessing anesthetic depth in rats using the up-and-down-design. It also provides a novel and detailed description and categorization of movement patterns in sedated rats when a standardized painful stimulus is applied to enhance reproducibility for future studies.