Effects of halothane dose and stimulus rate on canine spinal, far-field and near-field somatosensory evoked potentials.

Evidence that canine spinal, far-field and near-field somatosensory evoked potentials resemble those recorded in humans and other species has been presented, and the vulnerability of each component to varying depths of halothane anesthesia is reported. Lumbar spinal peak latencies are not affected by halothane dose, but the negative peak is significantly prolonged by rapid rates of stimulation. Elevated stimulus rates and halothane doses reduce lumbar spinal cord potential amplitudes. Early far-field cephalic components are refractory to halothane. Late far-field components and near-field cortical potentials are substantially altered by increments in halothane dose. Both near-field and far-field responses are more readily identified in vertex-neck than vertex-brow derivations. Early far-field somatosensory evoked potentials recorded from vertex to neck, together with lumbar spinal cord potentials, may be the preferred monitoring technique when the use of halothane anesthesia is desired. Rapid rates of stimulation may facilitate earlier recognition of cord dysfunction, but supplement rather than replace baseline recordings at slow stimulus rates.