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We evaluated changes in cardiovascular and renal functions as well as arginine vasopressin (AVP) secretion, with remifentanil and dexmedetomidine administration alone or in combination in sevoflurane-anesthetized dogs. Six healthy adult Beagle dogs received one of the following four treatments in a randomized crossover study: saline (C), remifentanil alone at successively increasing doses (R; 0.15, 0.60, and 2.40 μg/kg/min), dexmedetomidine alone (D; 0.5 μg/kg intravenously for initial 10 min followed by a constant rate infusion at 0.5 μg/kg/hr), and a combination of remifentanil and dexmedetomidine at the above-mentioned doses (RD). Sevoflurane doses were adjusted to 1.5 times of minimum alveolar concentration (MAC) equivalent according to MAC-sparing effects with remifentanil and dexmedetomidine as previously reported. Cardiovascular measurements, renal function data, and plasma AVP concentrations were determined before and every 60 min until 180 min after drug administration as per each treatment. In the R, D and RD, heart rate significantly decreased and mean arterial pressure significantly increased from baseline or with C. Cardiac index significantly decreased and systemic vascular resistance index increased with D and RD. Oxygen extraction ratio, renal blood flow, and glomerular filtration rate were not affected. The plasma AVP concentrations significantly decreased in D and RD, but increased in R. Only in D, the natriuresis was elicited. The combination of remifentanil and dexmedetomidine in sevoflurane-anesthetized dogs was acceptable in terms of the hemodynamics, oxygenation, and renal function. Remifentanil may interfere with dexmedetomidine-induced diuresis and inhibition of AVP secretion. [ABSTRACT FROM AUTHOR]

Remifentanil is an ultra-short-acting µ-opioid receptor agonist. The purpose of this study was to determine the relationship of the minimum alveolar concentration (MAC) of sevoflurane and other MAC derivatives, including the MAC for blocking adrenergic responses (MAC-BAR) and the MAC at which tracheal extubation is occurred (MAC-extubation), with or without remifentanil infusion. Six healthy adult beagle dogs were randomly anesthetized three times for determining the MAC-BAR (SEVMAC-BAR), MAC (SEVMAC), and MAC-extubation (SEVMAC-extubation) of sevoflurane under infusion of saline and remifentanil at rates of 0.15, 0.30, 0.60, 1.20, and 2.40 μg/kg/min. The ratio of the SEVMAC-BAR and SEVMAC and that of the SEVMAC-extubation and SEVMAC were not significantly different at baseline and during treatment. The MACBAR95 and MAC95 decreased in a dose-dependent manner until reaching 1.20 μg/kg/min, and the MAC-extubation5 decreased in a dose-dependent manner until reaching 0.60 μg/kg/min. The percentage reduction of SEVMAC-BAR, SEVMAC, and SEVMAC-extubation increased in a dose-dependent manner during remifentanil infusion. The heart rate significantly decreased in the MAC-BAR and MAC groups, and the systolic and mean arterial pressures increased after remifentanil infusion compared with the baseline values. Remifentanil infusion caused reduction of the SEVMAC-BAR, SEVMAC, and SEVMAC-extubation in a dose-dependent manner, and ceiling effects were observed in the dogs. Higher doses of remifentanil and sevoflurane were necessary for blocking the sympathetic response to the supramaximal stimulus to prevent movement and extubation in dogs. [ABSTRACT FROM AUTHOR]