LACK OF BETA-ADRENERGIC ACTIVITY OF ISOFLURANE IN THE DOG: A COMPARISON OF CIRCULATORY EFFECTS OF HALOTHANE AND ISOFLURANE AFTER PROPRANOLOL ADMINISTRATION

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Abstract
The studies were undertaken to determine whether isoflurane inhalation is associated with a degree of beta-adrenergic action that is potentially important in clinical situations, and to compare the circulatory tolerance to isoflurane and halothane in dogs following beta blockade. We measured arterial and pulmonary artery pressure, left and right ventricular filling pressure, heart rate and cardiac output, and derived stroke volume and systemic and pulmonary vascular resistances in 13 mongrel dogs. The haemodynamic response to 1 MAC and 2 MAC isoflurane was studied in seven dogs and was similar before and after propranolol 0.1 mg/kg i.v. In six dogs, propranolol 0.5 mg/kg caused no significant changes in the circulatory response to 1 MAC and 2 MAC isoflurane or 1 MAC halothane. However, in three dogs, administration of 2 MAC halothane after propranolol 0.5 mg/kg resulted in such profound circulatory depression as to preclude further study. These data suggest that (a) isoflurane possesses no clinically important beta-adrenergic stimulating activity; (b) there is no adverse drug interaction upon the circulation with the combination of isoflurane and propranolol; (c) in the presence of moderate to profound beta-adrenergic blockade, 2 MAC isoflurane may be tolerated better than 2 MAC halothane

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