Autonomic and cardiovascular effects of pentobarbital anesthesia during trigeminal stimulation in cats

Stimulation of the trigeminal nerve can elicit various cardiovascular and autonomic responses; however, the effects of anesthesia with pentobarbital sodium on these responses are unclear. Pentobarbital sodium was infused intravenously at a nominal rate and the lingual nerve was electrically stimulated at each infusion rate. Increases in systolic blood pressure (SBP) and heart rate (HR) were evoked by lingual nerve stimulation at an infusion rate between 5 and 7 mg·kg−1·h−1. This response was associated with an increase in the low-frequency band of SBP variability (SBP-LF). As the infusion rate increased to 10 mg·kg−1·h−1 or more, decreases in SBP and HR were observed. This response was associated with the reduction of SBP-LF. In conclusion, lingual nerve stimulation has both sympathomimetic and sympathoinhibitory effects, depending on the depth of pentobarbital anesthesia. The reaction pattern seems to be closely related to the autonomic balance produced by pentobarbital anesthesia. Anesthetized patients can experience potentially serious physiological responses to physical stimuli. For example, animal studies have revealed a ‘trigeminal depressor response’ (TDR), wherein stimulation of facial nerves under anesthesia triggers a marked decrease in blood pressure and heart rate. Since these studies have not considered the impact of depth of anesthesia, Hiroshi Hanamoto and colleagues at Japan’s Osaka University Graduate School of Dentistry examined the importance of this factor. They found that in lightly anesthetized cats, electrical stimulation of the lingual nerve actually led to increased heart rate and blood pressure; only under heavier anesthesia did such stimuli trigger TDR. This suggests that dental patients who faint during procedures could do so in response to pain, or fear of pain, rather than physiological changes induced by TDR, as was previously speculated.