Cardiorespiratory, hemodynamic, and sedative effects of dexmedetomidine in sheep.

An alternative in an attempt to minimize the effects triggered by intravenous (IV) bolus administration of α-2 adrenergic receptor agonists are continuous rate infusions (CRI). The requirement for sedation protocols in sheep for procedures to be performed without physical restraint and with reduced adverse effects, commonly observed with bolus use, justifies the study of CRI. The aim of study was to compare the cardiopulmonary and sedative effects of IV bolus injection and CRI of dexmedetomidine (DEX) in sheep. Six adult male sheep (38.3 ± 7.6 kg) received DEX as a bolus (5 µg kg^-1, DEX_bolus treatment) or CRI (5 µg kg^-1 h^-1 for 1 h, DEX_CRI treatment). We recorded heartrate (HR), respiratory rate, systemic arterial blood pressure, pulse oximetry, hemodynamic parameters, blood gases and sedation scores over 120 min. HR was significantly lower in DEX_bolus at 5 and 15 min than in DEX_CRI, with HR reduction observed for 30 min in DEX_bolus. Hypoxemia was noted in DEX_bolus at 10 and 30 min. Pulmonary vascular resistance index increased at 5 min, and cardiac index (CI) decreased at all timepoints compared with baseline in DEX_bolus. In DEX_CRI, CI decreased only at 45 min. Sedation scores were higher in DEX_bolus at 15 and 30 min. DEX CRI administration resulted in fewer cardiorespiratory and hemodynamic changes compared with bolus injection and lower sedation scores (<4/10), which would not allow animal handling without a reaction. The load dose used in CRI was a limitation to constant infusion.