Several hours into the experiment, and particularly when peripheral nerves were manipulated, an onset of tremoring and movement was observed in the animals. This movement was observed despite confirmation of the surgical anesthetic plane by means of nose pinch, jaw slackness, unresponsiveness to corneal reflex, and verification of other physiologic parameters such as temperature, blood glucose, and blood pH. The tremoring persisted despite increased dosing of Isoflurane and Fentanyl. Similar intraoperative shivering has been reported under different anesthetic conditions (Dubey, 2004). We found either intramuscular injection of Telazol (4-6 mg/kg) or intravenous Ketamine (10 mg/kg/hr) eliminated the tremoring. The effects of Telazol lasted for ~2 hours while Ketamine effects on tremoring washed in and out in ~15 minutes.
Telazol, Ketamine, and Isoflurane have a cardiac blunting effect, by which stimulation induced changes in cardiac function are blunted. As such, Telazol and Ketamine were not used during vagus nerve stimulation and Isoflurane dose was minimized. Instead, a muscle paralytic, Vecuronium (1-1.5 mg/kg/hr), was administered during vagus nerve recordings to abate recording artifact resulting from myogenic electric field spillover due to evoked muscle movement or ongoing tremoring – without cardiac blunting effects. A minimal dose of Isoflurane was still used as it permitted a ‘fast-dial’ (quick wash in and out period) to maintain the anesthetic plane.