TRANSCRANIAL MAGNETIC MOTOR EVOKED-POTENTIALS IN ANESTHETIZED DOGS

Transcranial magnetic motor evoked potentials (TMMEP) were recorded fr om the extensor carpi radialis muscle of the thoracic limb and from th e cranial tibial muscle of the pelvic limb in anesthetized dogs. All d ogs were premedicated with droperidol and fentanyl. Anesthesia was ind uced and maintained with either propofol, sufentanil and midazolam, th iopental, diazepam and ketamine, halothane, or nitrous oxide, the latt er both with and without fentanyl. The effect of different doses of th ese anesthetics upon onset latencies and peak-to-peak amplitudes of th e TMMEP was evaluated. Anesthetics produced a dose-dependent suppressi on of the TMMEP: latencies increased, amplitudes decreased, reproducib ility became poorer and the number of unsuccessful recordings increase d with increasing depth of anesthesia. Anesthesia using narcotics (suf entanil and midazolam, fentanyl and nitrous oxide) was considered supe rior to the other types of anesthesia because they produced the least suppression of the TMMEP and allowed TMMEP recording in all dogs, even at surgical planes of anesthesia.