We have examined the haemodynamic effects of 0.8% trichloroethylene and 1% halothane anaesthesia in a control group of five dogs, chronically implanted with cardiovascular flow- and pressure-measuring apparatus and compared them with a similar group of six dogs pretreated for 3 weeks with oral propranolol (20 mg/kg/day). The effects of graded haemorrhage of 25% of the estimated blood volume and re-transfusion were studied. Cardiovascular function was satisfactory at all stages of the study except during trichloroethylene anaesthesia in the beta-blocked dogs when the response to blood loss was impaired severely. Therefore the use of trichloroethylene in the presence of propranolol may not be advisable in clinical practice.
Oxprenolol is a non-selective adrenergic beta-receptor antagonist displaying beta-mimetic activity. To test the hypothesis that beta-mimetic activity could minimize the response of the circulation to adrenergic beta-receptor blockade, cumulative dose-response curves to oxprenolol 0.1-1.6 mg kg-1 were obtained in seven anaesthetized dogs. Anaesthesia was maintained with 0.5% halothane supplementing nitrous oxide 66% in oxygen, under moderately hypocapnic IPPV. Oxprenolol, up to 0.4 mg kg-1 i.v., caused modest increases in heart rate, LV dP/dt max and cardiac output. With the largest dose (1.6 mg kg-1), significant increases in heart rate (+19%), LV dP/dt max (+13%) and cardiac output (+27%) were observed while arterial pressure remained unchanged and systemic vascular resistance decreased (-18%).
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