Evaluation of analgesic and sedative effects of continuous infusion of dexmedetomidine by measuring somatosensory- and auditory-evoked potentials in the rat

OBJECTIVE: To study, the analgesic and sedative effects of different constant rate infusions (CRI) of dexmedetomidine, in the rat, by measurement of specific electroencephalographic parameters. The recorded parameters were somatosensory-evoked potentials (SEPs) and auditory-evoked potentials (AEPs), which have been shown to be related to analgesia and sedation respectively.

ANIMALS: Nine male Wistar rats (HsdCpb:Wu, Harlan Netherlands BV, body weight 300-350 g).

METHODS: Somatosensory-evoked potentials were recorded from the primary somatosensory cortex and the vertex location (SI/Vx-SEPs). Auditory-evoked potentials were recorded from the primary auditory cortex and vertex location (AI/Vx-AEPs). Primary somatosensory cortex and vertex location recorded SEPs and AI/Vx-AEPs were recorded alternately, during CRI of dexmedetomidine (4.0, 10.0, 20.0 microg kg(-1) hour(-1)) and a control (saline).

RESULTS: The primary somatosensory cortex-evoked potentials were not affected by the dexmedetomidine CRI, but the other three parameters were significantly affected; although the AI-SEP to a lesser extent than the Vx-SEP and Vx-AEP. A maximum effect on the Vx-AEP was reached at lower doses than on the Vx-SEP.

CONCLUSIONS: Based on the present findings, it is suggested that CRI of dexmedetomidine provided profound sedation at low doses, whereas higher doses are needed to provide concurrent analgesia.

CLINICAL RELEVANCE: A constant rate infusion of dexmedetomidine can be a valuable adjunct in the provision of sedation and/or analgesia. However, analgesia cannot be produced without sedation, and sedation is not necessarily accompanied by comparative degrees of analgesia.