Abstract
Multifocal ventricular beats during hypothermia may herald impending ventricular fibrillation. Propranolol and lidocaine are effective in the control of ventricular dysrhythmia at normal body temperature, however, the negative inotropic effect of either drug may further depress the cardiovascular function in a hypothermic patient. The results could be just as fatal as ventricular fibrillation. We studied the negative inotropic effects of propranolol and lidocaine in the dog under pentobarbital anesthesia. Hypothermia was induced through a venovenous shunt; allowed to stabilize at 25°C for 1 hr, and then rewarmed through an arteriovenous shunt utilizing a heat exchanger. The presence of premature ventricular beats or other dysrhythmia was not a prerequisite for the study. The dogs received propranolol (0.3 mg/kg) or lidocaine (50 mg initially plus continuous infusion of 40–50 μg/kg/min) intravenously at the end of the 1-hr stabilization, just before rewarming. Control animals received 10 ml saline intravenously. The arteriovenous shunt functioned at the time the drugs were administered. The results suggest that: (i) hypothermia in this model impairs circulatory function; (ii) lidocaine or propranolol do not significantly decrease circulatory function; (iii) rapid core rewarming reverses the effects of hypothermia; (iv) propranolol has minimal effects on the hemodynamic course during rewarming when compared to untreated controls; and (v) lidocaine treatment produces a more desirable course during rewarming. Our findings show that in the acutely hypothermic dog, therapeutic doses of propranolol or lidocaine do not further decrease an already depressed cardiovascular state.
Published Version
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