RELATION BETWEEN BODY-TEMPERATURE AND DEXMEDETOMIDINE-INDUCED MINIMUM ALVEOLAR CONCENTRATION AND RESPIRATORY CHANGES IN ISOFLURANE-ANESTHETIZED MINIATURE SWINE

Dexmedetomidine (DFX), an alpha(2)-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 mu g/kg of body weight)-induced changes in body temperature. AU 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 Pa-CO2 was lower and, accordingly, pH was higher in these swine. Blood pressure and heart rate were not affected by temperature changes.