Neurophysiological assessment of the sedative and analgesic effects of a constant rate infusion of dexmedetomidine in the dog.

The sedative and analgesic effects of continuous rate infusion (CRI) of dexmedetomidine (DEX) were investigated in Beagle dogs (n=8) using auditory and somatosensory evoked potentials (AEPs and SEPs) recorded before, during and after a CRI of saline or DEX (1.0, 3.0, 5.0 μg/kg bolus, followed by 1.0, 3.0, 5.0 μg/kg/h CRI, respectively). The results showed a significant reduction in AEP at doses of 1.0 μg/kg/h and above and a significant reduction of the SEP at doses of 3.0 and 5.0 μg/kg/h. Neither the AEP nor the SEP was further reduced at 5.0 μg/kg/h when compared to 3.0 μg/kg/h, although a slower return towards baseline values was observed at 5.0 μg/kg/h. The mean plasma levels (±SEM) of DEX during infusion were 0.533±0.053 ng/mL for the 1.0 μg/kg/h dose, 1.869±0.063 ng/mL for the 3.0 μg/kg/h dose and 4.017±0.385 for the 5.0 μg/kg/dose. It was concluded that in adult dogs, a CRI of DEX had a sedative and analgesic effect that could be described quantitatively using neurophysiological parameters. Sedation was achieved at lower plasma levels than required for analgesia, and DEX had a longer (but not larger) effect with infusion rates above 3.0 μg/kg/h.