Influence of body size on tibial nerve somatosensory evoked potentials in dogs.

Somatosensory evoked potentials in response to tibial nerve stimulation were recorded from the scalp of 31 clinically normal mixed-breed dogs. The latency and amplitude of a main positive potential (P18), recorded with a frontal electrode referenced to the nose, were measured in subjects with body length ranging from 316 to 962 mm. A linear relation to body size explained the variations in latency among dogs (r2 = 0.81); the amplitude variations were explained in part by body size (r2 = 0.44). Bilateral tibial nerve stimulation significantly (P < 0.05) increased the amplitude of P18, but its latency was unaffected, compared with unilateral stimulation. Results of unilateral right and left tibial nerve stimulation were compared and were not different. Replacing acepromazine with xylazine as premedication before thiopental anesthesia did not influence the recordings.