Minimum alveolar concentration measures of central nervous system activation in cats anesthetized with isoflurane

Philip A. March Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

Search for other papers by Philip A. March in
Current site
Google Scholar
PubMed
Close
 DVM, MS
and
William W. Muir III Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210.

Search for other papers by William W. Muir III in
Current site
Google Scholar
PubMed
Close
 DVM, PhD

Abstract

Objective—To compare the minimum alveolar concentration (MAC) of isoflurane required to prevent corticocerebral activation, autonomic responses, and purposeful movements after somatic or visceral stimulation in cats anesthetized with isoflurane.

Animals—17 healthy spayed female cats.

Procedure—Bispectral index (BIS), autonomic parameters, and purposeful movements were monitored before and after somatic or visceral stimuli in cats anesthetized with isoflurane. End-tidal (ET) isoflurane concentration was varied to determine MAC values for cortical arousal (MACBIS), autonomic responsiveness (MACBAR), and purposeful movement (MAC). Bispectral index values ≥ 60 were considered to represent corticocerebral activation.

Results—Minimum alveolar concentration for purposeful movement was significantly less than MACBIS and MACBAR for both somatic and visceral stimulation. Individual MAC values for somatic stimulation were not significantly different from respective MAC values for visceral stimulation. The percentage of cats that had a BIS response ≥ 60 was inversely related to the end-tidal isoflurane concentration.

Conclusions and Clinical Relevance—Corticocerebral arousal and subcortical autonomic reflexes occured at isoflurane anesthetic concentrations at which reflexive or purposeful movements were absent. These results suggested that isoflurane had a preferential effect on voluntary motor output at low end-tidal isoflurane concentrations, and that sensory pathways, subcortical sympathetic output, and cortical responsiveness are less susceptible to the anesthetic effects of isoflurane. Bispectral index values obtained after somatic or visceral stimulation were sensitive for the detection of early changes in cortical excitability. (Am J Vet Res 2003; 64:1528–1533)

Abstract

Objective—To compare the minimum alveolar concentration (MAC) of isoflurane required to prevent corticocerebral activation, autonomic responses, and purposeful movements after somatic or visceral stimulation in cats anesthetized with isoflurane.

Animals—17 healthy spayed female cats.

Procedure—Bispectral index (BIS), autonomic parameters, and purposeful movements were monitored before and after somatic or visceral stimuli in cats anesthetized with isoflurane. End-tidal (ET) isoflurane concentration was varied to determine MAC values for cortical arousal (MACBIS), autonomic responsiveness (MACBAR), and purposeful movement (MAC). Bispectral index values ≥ 60 were considered to represent corticocerebral activation.

Results—Minimum alveolar concentration for purposeful movement was significantly less than MACBIS and MACBAR for both somatic and visceral stimulation. Individual MAC values for somatic stimulation were not significantly different from respective MAC values for visceral stimulation. The percentage of cats that had a BIS response ≥ 60 was inversely related to the end-tidal isoflurane concentration.

Conclusions and Clinical Relevance—Corticocerebral arousal and subcortical autonomic reflexes occured at isoflurane anesthetic concentrations at which reflexive or purposeful movements were absent. These results suggested that isoflurane had a preferential effect on voluntary motor output at low end-tidal isoflurane concentrations, and that sensory pathways, subcortical sympathetic output, and cortical responsiveness are less susceptible to the anesthetic effects of isoflurane. Bispectral index values obtained after somatic or visceral stimulation were sensitive for the detection of early changes in cortical excitability. (Am J Vet Res 2003; 64:1528–1533)

Advertisement