CARDIOVASCULAR INTERACTIONS OF LOCAL-ANESTHETICS AND CALCIUM ENTRY BLOCKERS IN CONSCIOUS DOGS

To assess the pharmacologic risk of regional anesthesia in patients treated with calcium entry blockers (CEBs), the cardiovascular effects of 30-minute infusions of lidocaine (60-mu-g . kg-1 . minute-1 after an intravenous bolus of 1.5 mg . kg-1), bupivacaine (15-mu-g . kg-1 . minute-1 after an intravenous bolus of 0.4 mg . kg-1) or normal saline (1 ml . minute-1) were studied with concurrent 40-minute infusions of equihypotensive doses of verapamil (25-mu-g . kg-1 . minute-1) and diltiazem (20-mu-g . kg-1 . minute-1) in seven conscious dogs chronically instrumented for continuous recording of arterial pressure and left ventricular (LV) contractility assessed by the peak of LV dP/dt. The effects of CEBs alone (saline group) were stable throughout the infusion time. Besides a 10% decrease in mean arterial pressure, verapamil increased heart rate, prolonged atrioventricular (AV) conduction and decreased LV dP/dt, whereas a lesser and isolated tachycardia was observed in the case of diltiazem. At the end of a 30-minute concomitant infusion: (1) bupivacaine (1.4-mu-g/ml) further decreased arterial pressure (with verapamil and diltiazem; -8% and -11%, respectively) and LV dP/dt (with verapamil, -13%), whereas PR interval was further lengthened with verapamil and diltiazem (+36% and +17%, respectively) without change in heart rate; (2) lidocaine (almost-equal-to 3.5-mu-g/ml) increased heart rate (with verapamil and diltiazem; +19% and +14%, respectively) and arterial pressure (with verapamil, +8%) without change in LV dP/dt, while the PR interval was further lengthened during verapamil infusion (+34%). Second-degree AV blocks appeared with lidocaine (one of seven dogs) and bupivacaine (three of seven dogs) during verapamil infusion. Caution should therefore be exercised when patients under effective verapamil or diltiazem treatment are given regional anesthesia resulting in significant plasma levels of local anesthetics. Because of a lesser deleterious cardiovascular interaction with both verapamil and diltiazem, lidocaine would be preferable to bupivacaine in such a circumstance.