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Lumbosacral spinal cord somatosensory evoked potentials for quantification of nociception in horses
Author(s) -
Van LOON J. P. A. M.,
Van OOSTROM H.,
DOORNENBAL A.,
HELLEBREKERS L. J.
Publication year - 2010
Publication title -
equine veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.82
H-Index - 87
eISSN - 2042-3306
pISSN - 0425-1644
DOI - 10.1111/j.2042-3306.2009.00023.x
Subject(s) - nociception , medicine , lumbosacral joint , somatosensory evoked potential , anesthesia , spinal cord , analgesic , stimulation , somatosensory system , noxious stimulus , anatomy , receptor , psychiatry
Summary Reasons for performing study: There is a need for objective evaluation and quantification of the efficacy of analgesic drugs and analgesic techniques in horses. Objectives: To determine whether lumbosacral spinal cord somatosensory evoked potentials (SSEP) can be a useful and reliable tool to assess nociception in equines. Methods: SSEPs and electromyograms (EMG) from the epaxial muscles were recorded simultaneously, following electrical stimulation applied to the distal hindlimb in lightly anaesthetised Shetland ponies (n = 7). In order to validate the model, the effect of increasing stimulus intensity was documented and the conduction velocities (CV) of the stimulated nerves were calculated. The effect of epidurally applied methadone (0.4 mg/kg bwt) in a randomised, crossover design was investigated. Results: Two distinct complexes (N1P1 and N2P2) were identified in the SSEP waveform. Based on their latency and conduction velocity and the depressant effect of epidurally applied methadone, the SSEP N2P2 was ascribed to nociceptive Aδ‐afferent stimulation. The SSEP N1P1 originated from non‐nociceptive Aβ‐afferent stimulation and was not influenced by epidurally applied methadone. Conclusions and potential relevance: The nociceptive Aδ component of the SSEP, the N2P2 complex, is presented as a valid and quantitative parameter of spinal nociceptive processing in the horse. Validation of the equine SSEP model enables the analgesic effects of new analgesics/analgesic techniques to be quantified and analgesia protocols for caudal epidural analgesia in equidae improved.