title: Cardiorespiratory and minimum alveolar concentration sparing effects of a continuous intravenous infusion of dexmedetomidine in halothane or isoflurane-anaesthetized rats.
abstract: Dexmedetomidine (DEX) is a highly selective alpha(2)-adrenoceptor agonist in both the central and peripheral nervous systems. Its cardiorespiratory effects have been described; however, these effects have not been reported when it is used in combination with volatile anaesthetics in rats. The cardiovascular and respiratory actions of a continuous intravenous infusion of 0.25 microg/kg/min of DEX administered to rats anaesthetized at 1 minimum alveolar concentration (MAC) of either halothane (HAL) or isoflurane (ISO) were studied. Twenty-eight rats were grouped into four treatment groups: HAL alone, ISO alone, DEX + HAL and DEX + ISO. The MAC(HAL) or MAC(ISO) was determined in each rat from alveolar gas samples at the time of tail clamping. Control MAC values, expressed as mean +/- standard deviation, were 1.31 +/- 0.1% for HAL and 1.46 +/- 0.05% for ISO. DEX reduced HAL MAC from 1.31 +/- 0.1% to 0.36 +/- 0.22% (72 +/- 17% MAC reduction) and ISO MAC from 1.46 +/- 0.05% to 0.83 +/- 0.2% (43 +/- 14% MAC reduction). Heart rate (HR) was decreased in both DEX groups at 1 MAC, with no differences between HAL and ISO. The mean arterial pressure was significantly depressed in the DEX + ISO group compared with the ISO only group. This difference in mean arterial blood pressure (MABP) was not seen between the DEX + HAL and HAL only groups. Respiratory depression was minor at 1 MAC with both inhalant anaesthetics. DEX reduced the MAC of HAL to a degree greater than it decreased the MAC of ISO. The effects of DEX on HR and ventilation were similar in rats anaesthetized with HAL or ISO at 1 MAC; however, hypotension was more pronounced when DEX was combined with ISO at 1 MAC.
authors.affiliation: Servicio de Cirugía Experimental, Hospital Universitario Puerta de Hierro, C/ San Martín de Porres 4, 28035 Madrid, Spain.
authors.forename: E
authors.initials: E
authors.lastname: Rioja
authors.forename: M
authors.initials: M
authors.lastname: Santos
authors.forename: F
authors.initials: F
authors.lastname: Martínez Taboada
authors.forename: J A
authors.initials: JA
authors.lastname: Ibancovichi
authors.forename: F J
authors.initials: FJ
authors.lastname: Tendillo
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000769:Anesthesia, Inhalation; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D020927:Dexmedetomidine / Q000494:pharmacology*; D004357:Drug Synergism; D005260:Female; D006221:Halothane / Q000008:administration & dosage*; D006321:Heart / Q000187:drug effects*; D006339:Heart Rate / Q000187:drug effects; D007262:Infusions, Intravenous; D007530:Isoflurane / Q000008:administration & dosage*; D011650:Pulmonary Alveoli / Q000187:drug effects* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012119:Respiration / Q000187:drug effects; D013047:Specific Pathogen-Free Organisms
chemical_list: D000316:Adrenergic alpha-Agonists; D018685:Anesthetics, Inhalation; D020927:Dexmedetomidine; D007530:Isoflurane; D006221:Halothane