Toxicity and resuscitation in lidocaine- or bupivacaine-infused cats

Controversy persists surrounding the relative safety of bupivacaine compared with lidocaine especially with regard to its cardiovascular toxicity and the ability to resuscitate following such occurrences. The margin of safety between seizure onset and cardiovascular collapse was compared in lightly anesthetized and ventilated cats given an equipotent infusion of either lidocaine or bupivacaine (N = 10 for each group). The infusion rates were 4 mg X kg-1 X min-1 bupivacaine or 16 mg X kg-1 X min-1 lidocaine. Onset of electrical seizure activity occurred at about the same time in both groups and was defined as the central nervous system (CNS) toxic end point. The infusion continued until the mean arterial pressure reached 10 mmHg (cardiotoxic end point). Despite the early occurrence of electrocardiographic changes in the bupivacaine group, mean arterial pressure was greater and sustained significantly longer (4.9 +/- 1.3 min; mean +/- SD) with this drug compared with lidocaine (3.0 +/- 0.6 min) (P less than 0.005). Using the blood pressure criterion for defining cardiovascular (CV) collapse, the CV/CNS toxicity ratio for drug dosage was 4.0 with lidocaine and 4.8 with bupivacaine. The use of a standardized resuscitation protocol made it possible to compare the ability to resuscitate animals in each group. Despite very high plasma local anesthetic concentrations, all lidocaine-infused animals were quickly resuscitated (4.4 +/- 3.0 min; mean +/- SD). The resuscitation time for the bupivacaine group (5.4 +/- 2.4 min) was similar. Two cats in the bupivacaine group could not be brought to resuscitation criterion, a difference, however, that was not statistically significant.