Hemodynamic and coronary vascular effects of dexmedetomidine in the anesthetized goat

Background: In phase III trials, the hemodynamic stabilising effect of the α₂-adrenergic agonist dexmedetomidine (DEX) is being investigated in patients with coronary artery disease. Coronary vascular effects of α₂-agonists have been studied in dogs and pigs, but both species have a different hemodynamic response to DEX than man. The aim of this study was to investigate the hemodynamic and coronary vascular effects in goats.
Methods: In 6 open-chest goats anesthetized with halothane, central and coronary hemodynamics and oxygen supply and demand were measured before and following IV bolus infusion of DEX in doses ranging from 0.1 to 10 μg/kg.
Results: With DEX doses of 1 μg/kg or higher, mean arterial pressure (MAP), systemic vascular resistance, coronary vascular resistance and arterio-mixed venous oxygen content increased within 2 min, but returned to baseline within 15 min. In contrast, there was a progressive and cumulative decrease in cardiac output (CO), heart rate, and dP/dt_max. Regional coronary venous oxygen extraction (C(a-cv)O₂) transiently increased after 3 μg/kg DEX and decreased 15 min after 10 μg/kg DEX. LVEDP transiently increased after 3 and 10 μg/kg DEX. The changes after DEX 10 μg/kg differed from those after lower doses: MAP (35%), CO (50%), stroke volume (33%), C(a-cv)O₂ (15%) and myocardial oxygen extraction (33%) were all decreased. Myocardial oxygen supply and demand decreased in parallel.
Conclusions: 1) The cardiovascular response to IV DEX in goats is similar to man. 2) In goats after DEX, systemic and coronary vasoconstriction are short-lived, and 3) the balance between myocardial oxygen supply and demand is maintained.