Cardiovascular Effectsv of Convulsant and Supraconvulsant Doses of Amide Local Anesthetics

Because resuscitation from toxic responses to bupivacaine (B) or etidocaine (E) is said to be difficult, the cardiovascular effects of these two local anesthetics were compared with those of lidocaine (L) in 40 lightly anesthetized, ventilated cats. First, the circulatory effects of a threshold convulsant dose (1 × CD) of local anesthetic were determined. One hour later, local anesthetic was infused beyond the onset of convulsions until the blood pressure (BP) decreased to less than 50 torr, or until the electroencephalogram (EEG) became flat. When drugs were infused at equiconvulsant rates (1 mg/kg/min for B and E; 4 mg/kg/min for L), electrical convulsions began after 4 to 6 minutes. Nodal and ventricular cardiac arrhythmias regularly appeared with B and E, but not with L. BP increased with B and E, but decreased slightly with L. B and E seizures lasted approximately 2 times longer than L seizures; BP and electrocardiogram (ECG) returned to control levels within 10 minutes. After full recovery, local anesthetic infusion was restarted; all cats survived at least 2 × CD. Arrhythmias reappeared after approximately 0.6 × CD of B or E. Only eight of 15 cats had arrhythmias after 2 × CD of L. After the onset of seizures, BP decreased progressively with B or E, more rapidly with L. When BP reached 50% of control levels after 2.3 × CD of L, 12 cats were given ephedrine, 1 mg, and survived 3 × CD of L; of the other three cats, two died before 3 × CD of L. Cats given B or E did not require ephedrine, and eight of nine B and 13 of 15 E cats recovered after 3 × CD. It is concluded that cats survive at least 2 times the convulsant dose of amide local anesthetics, provided oxygenation and ventilation are supported. With higher doses, cardiac arrhythmias and hypotension increasingly compromise circulation.