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Open Access Movement As an Index of Anesthetic Depth in Humans and Experimental Animals

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Anesthesia is used widely in animal research, but there are diverse opinions regarding acceptable anesthetic depth. Excessive anesthesia is associated with increased morbidity and mortality. Traditionally, researchers have been taught that animal movement during surgical and experimental procedures indicates that the animal is 'underanesthetized.' Complex movement, however, can be initiated and propagated within the spinal cord, with little input from supraspinal structures. For example, frogs with high spinal-cord transections still maintain the wiping reflex, whereby the hindlimb can move to the forelimb to wipe away a noxious stimulus. Rats that have been decerebrated can perform complex tasks, such as grooming. Brain-dead humans can have spontaneous movement of the arms, legs, and head. Consistent with these phenomena, emerging evidence suggests that, in anesthetized animals, movement in response to noxious stimulation is abolished primarily via anesthetic action in the spinal cord. When isoflurane, halothane, or thiopental is delivered selectively to the brain circulation in goats, substantially greater anesthetic concentrations in brain are needed to ablate movement, as compared with those required upon delivery of anesthetic to the entire body. Rats that have had a precollicular decerebration require the same isoflurane concentrations to prevent movement as compared to intact rats. Furthermore, data from both humans and animals indicate that memory and awareness are ablated at anesthetic concentrations that are <50% of those needed to abolish movement. Collectively, these data indicate that animals can be anesthetized at depths that, although they do not abolish movement, still produce unconsciousness and amnesia.

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Document Type: Miscellaneous

Affiliations: 1: Department of Anesthesiology and Pain Medicine, Section of Neurobiology, Physiology and Behavior, University of California, Davis 2: Department of Anesthesiology and Pain Medicine, University of California, Davis 3: Section of Neurobiology, Physiology and Behavior, University of California, Davis

Publication date: 2005-10-01

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  • Comparative Medicine (CM), an international journal of comparative and experimental medicine, is the leading English-language publication in the field and is ranked by the Science Citation Index in the upper third of all scientific journals. The mission of CM is to disseminate high-quality, peer-reviewed information that expands biomedical knowledge and promotes human and animal health through the study of laboratory animal disease, animal models of disease, and basic biologic mechanisms related to disease in people and animals.

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