INTERACTIONS OF BETA-RECEPTOR BLOCKADE AND Pco 2 LEVELS IN THE ANAESTHETIZED DOG

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Abstract
The interactions of beta-receptor blockade (propranolol) and Pco2 levels were studied in dogs anaesthetized with halothane or nitrous oxide. The cardiovascular responses to beta-receptor blockade were found to be minimal during normocapnia and halothane anaesthesia, whereas during hypocapnia or hypercapnia more marked responses to beta-receptor blockade were observed (diminution of heart rate, cardiac output and myocardial contractility; augmentation of systemic vascular resistance). With nitrous oxide anaesthesia, the cardiovascular responses to beta-receptor blockade were similar in direction but much more pronounced than with halothane anaesthesia; marked increases in systemic vascular resistance were induced by beta-receptor blockade at all Pco2 levels. Since the overall haemodynamic response to beta-receptor blockade is dependent on the prevailing level of sympathetic nervous activity, which is itself modified in a complex way by anaesthesia and the levels of Pco2, it is not possible to define a standard response to beta-receptor blockade except under clearly specified conditions.

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