[Do beta adrenergic receptor blockaders increase bupivacaine cardiotoxicity?]

Bupivacaine is known to impair the electrophysiology of the heart as well as haemodynamic parameters. Administration of calcium channel blockers prior to bupivacaine enhances its cardiotoxicity. This study assessed the effects of bupivacaine at toxic dose in dogs with previous beta-adrenergic receptor blockade. It included 12 dogs anaesthetized with thiopentone, allocated in a control group (n = 6) receiving a bolus of bupivacaine (4 mg.kg-1) and a study group (n = 6) treated with the sequence propranolol (0.2 mg.kg-1) and bupivacaine (4 mg.kg-1), 15 min later. Infranodal conduction (HV conduction times and QRS durations) was worsened in both groups. Previous propranolol administration had no potentiating effects on these parameters. Conversely the latter was responsible of a greater decrease in heart rate, and increase in atrio-ventricular conduction time (77.9% vs 18.7%, p less than 0.05), as well as a more severe hypotension. Moreover, 3 out of the 6 animals in the study group suffered a cardiac arrest between the 5th and the 10th min. It is concluded that in anaesthetized dogs the cardiac and circulatory effects of a toxic dose of bupivacaine are increased in case of preexisting blockade of beta adrenergic receptors.