Relation between body temperature and dexmedetomidine-induced minimum alveolar concentration and respiratory changes in isoflurane-anesthetized miniature swine

Outi M. Vainio From the Department of Anesthesiology, University of California, Los Angeles, 10833 LeConte Ave, Los Angeles, CA 90024-1778.

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 DVM, PhD
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B. C. Bloor From the Department of Anesthesiology, University of California, Los Angeles, 10833 LeConte Ave, Los Angeles, CA 90024-1778.

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Summary

Dexmedetomidine (dex), an α2-receptor agonist, is the pharmacologically active d-isomer of medetomidine, a compound used as a sedative in veterinary medicine. Isoflurane anesthetic requirement (minimum alveolar concentration; mac), rectal temperature, and cardiorespiratory variables were studied in chronically instrumented Yucatan miniature swine during dex (20 μg/kg of body weight)-induced changes in body temperature. All studies were performed at room temperature of 22 C. The dex was given as a 2-minute infusion into the left atrium. Each pig was studied twice. For protocol 1, the core temperature of the pigs was maintained at (mean ± SD) 38.2 ± 0.5 C by use of a thermostatically controlled water blanket and a heating lamp. For protocol 2, the core temperature was not externally manipulated and it decreased from 38.2 ± 0.4 C to 32.2 ± 1.2 C during the more than 3 hours of the protocol. Control isoflurane mac was 1.66 ± 0.2% and was 1.74 ± 0.3% for protocols 1 and 2, respectively; dex decreased mac by 34 and 44%, respectively. For protocol 1, reduction in mac after dex administration returned by 50 and 80% at 84 and 138 minutes, respectively. If rectal temperature was not maintained (eg, allowed to decrease), mac was reduced by 57% at the same time as the return to 80% in the swine with maintained body temperature. Respiratory rate and minute ventilation were significantly higher in swine with maintained temperature. The PaCO2, was lower and, accordingly, pH was higher in these swine. Blood pressure and heart rate were not affected by temperature changes.

Summary

Dexmedetomidine (dex), an α2-receptor agonist, is the pharmacologically active d-isomer of medetomidine, a compound used as a sedative in veterinary medicine. Isoflurane anesthetic requirement (minimum alveolar concentration; mac), rectal temperature, and cardiorespiratory variables were studied in chronically instrumented Yucatan miniature swine during dex (20 μg/kg of body weight)-induced changes in body temperature. All studies were performed at room temperature of 22 C. The dex was given as a 2-minute infusion into the left atrium. Each pig was studied twice. For protocol 1, the core temperature of the pigs was maintained at (mean ± SD) 38.2 ± 0.5 C by use of a thermostatically controlled water blanket and a heating lamp. For protocol 2, the core temperature was not externally manipulated and it decreased from 38.2 ± 0.4 C to 32.2 ± 1.2 C during the more than 3 hours of the protocol. Control isoflurane mac was 1.66 ± 0.2% and was 1.74 ± 0.3% for protocols 1 and 2, respectively; dex decreased mac by 34 and 44%, respectively. For protocol 1, reduction in mac after dex administration returned by 50 and 80% at 84 and 138 minutes, respectively. If rectal temperature was not maintained (eg, allowed to decrease), mac was reduced by 57% at the same time as the return to 80% in the swine with maintained body temperature. Respiratory rate and minute ventilation were significantly higher in swine with maintained temperature. The PaCO2, was lower and, accordingly, pH was higher in these swine. Blood pressure and heart rate were not affected by temperature changes.

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