Anaesthetic problems associated with the treatment of cardiovascular disease: II. Beta-adrenergic antagonists.

Abstract

There are a number of beta-adrenergic antagonists available for general clinical use. The pharmacological action of these agents in patients with ischaemic heart disease and hypertensive cardiovascular disease is similar to that of the prototype, propranolol. No less than three per cent of patients treated with propranolol develop life-threatening cardiac complications. Since the combined circulatory depressant effect of beta blockade and anaesthesia is a cause for concern, surgical patients, who are also treated with beta an-tagonists for their cardiovascular disease, should be properly assessed and prepared. Due to individual differences in receptor sensitivity, pharmacokinetic factors and compliance with treatment, the daily maintenance dose does not reflect the degree of beta blockade. A thorough examination of the cardiovascular system is helpful. There is no reason to withhold or reduce the maintenance dose before surgery in the optimally treated patient; but corrective measures are necessary in the patient on a toxic dose. Choice of anaesthetic agents should be made according to known interactions between these agents and beta-adrenergic antagonists. The combined circulatory depressant effect of halothane as well as morphine and beta blockade is additive, while that of enflurane and beta blockade is less predictable. There is minimal interaction between isoflurane and propranolol, but the combination of methoxyflurane and practolol seems to be unacceptable. There are both practical and theoretical disadvantages to the use of succinylcholine because of its muscarinic action and the use of d-tubocurarine because of its ganglionic blocking effect. On the other hand, no objection to the use of dimethyl-tubocurarine and pancuronium exists. To avoid adverse interaction, neostigmine should be given in small increments, and only after the administration of atropine. Since acute myocardial infarction can strike as early as twenty-four hours after abrupt withdrawal, the surgical patient treated with beta antagonists should be allowed to go back to his maintenance dose as early as possible after operation. For patients who have to abstain from oral intake postoperatively, intravenous infusion of propranolol is recommended. If life-threatening bradycardia and hypotension should develop, the use of beta agonists can overcome the competitive beta-adrenergic blockade. Atropine, aminophylline, cardiac glycosides, calcium salts and glucagon can also be used to counteract the circulatory effects of beta antagonists.