Background: We assessed the relationship between patient age and remifentanil dosing rate in patients managed under general anesthesia with spontaneous breathing using low-dose remifentanil in sevoflurane. Methods: The participants were patients with an American Society of Anesthesiologists Physical Status of 1 or 2 maintained under general anesthesia with low-dose remifentanil in 1.5-2.0% sevoflurane. The infusion rate of remifentanil was adjusted so that the spontaneous respiratory rate was half the rate prior to the induction of anesthesia, and γH 　(µg/kg/min) was defined as the infusion rate of remifentanil under stable conditions where the respiratory rate was half the rate prior to the induction of anesthesia for ≥ 15 minutes. The relationship between γH and patient age was analyzed statistically by Spearman's correlation analysis. Results: During dental treatment under general anesthesia using low-dose remifentanil in sevoflurane, a significant correlation was detected between γH and patient age. The regression line of y = − 0.00079 x + 0.066 (y-axis; γH , x-axis; patient's age) was provided. The values of γH provide 0.064 µg/kg/min at 2 years and 0.0186 µg/kg/min at 60 years. Therefore, as age increases, the dosing rate exhibits a declining trend. Furthermore, in the dosing rate of remifentanil when the patient's respiratory rate was reduced by half from the preanesthetic respiratory rate, the dosing rate provided was around 0.88 mL/h in all ages if the remifentanil was diluted as 0.1 mg/mL. EtCO2 showed 51.0 ± 5.7 mmHg, and SpO2 was controlled within the normal range by this method. In addition, all dental treatments were performed without major problems, such as awakening and body movement during general anesthesia, and the post-anesthetic recovery process was stable. Conclusion General anesthesia with spontaneous breathing provides various advantages, and the present method is appropriate for minimally invasive procedures.

Background: Recent animal studies have suggested the role of GABA type A (GABA- A ) receptors in salivation, showing that GABA- A receptor agonists inhibit salivary secretion. This study aimed to evaluate the effects of propofol (a GABA- A agonist) on salivary secretions from the submandibular, sublingual, and labial glands during intravenous sedation in healthy volunteers. Methods: Twenty healthy male volunteers participated in the study. They received a loading dose of propofol 6 mg/kg/h for 10 min, followed by 3 mg/kg/h for 15 min. Salivary flow rates in the submandibular, sublingual, and labial glands were measured before, during, and after propofol infusion, and amylase activity was measured in the saliva from the submandibular and sublingual glands. Results: We found that the salivary flow rates in the submandibular, sublingual, and labial glands significantly decreased during intravenous sedation with propofol (P < 0.01). Similarly, amylase activity in the saliva from the submandibular and sublingual glands was significantly decreased (P < 0.01). Conclusion It can be concluded that intravenous sedation with propofol decreases salivary secretion in the submandibular, sublingual, and labial glands via the GABA- A receptor. These results may be useful for dental treatment when desalivation is necessary.