Hemodynamic effects of inotropes during hypothermia and rapid rewarming

The hemodynamic effects of propranolol, lidocaine, and dopamine were studied in anesthetized, mechanically ventilated dogs, cooled to 25 degrees C with a venovenous shunt through a heat exchanger. After 1 h at 25 degrees C, the shunt was converted to an arteriovenous shunt which remained functional until the study was completed. Before rewarming, the authors treated each group of 8 dogs with intravenous doses of the drugs: group 1: 10 ml saline as control; group 2: propranolol 0.3 mg/kg; group 3: 50 mg lidocaine initially, followed with continuous infusion of 40-50 microgram/kg.min; group 4: dopamine infusion at 12 microgram/kg.min; and group 5: lidocaine as in group 3 and dopamine as in group 4. For the dopamine-treated groups, 2 min of infusion was allowed; in all other groups, 5 min elapsed after injection before the hemodynamic data were recorded. The hemodynamic data were collected at esophageal temperatures of 25, 30, and 37 degrees C. The findings were: (1) hypothermia impaired cardiovascular function; (2) lidocaine and propranolol had minimal hemodynamic effects during hypothermia; lidocaine was physiologically more desirable than propranolol; (3) dopamine, alone or combined with lidocaine, reversed the cardiovascular depression from hypothermia; the improvement was equivalent to rewarming by as much as 5 degrees C; and (4) at the completion of rewarming, cardiovascular recovery was more complete with dopamine/lidocaine-treated animals compared to untreated and propranolol-treated animals. Based on these findings, these inotropes appear to be safe adjuncts to resuscitation during hypothermia.