One-way valves in breathing tubing reduce dead space during spontaneous breathing in anesthetized piglets

The circle breathing system was unsafe for spontaneous breathing because of hypercapnia during anesthesia. Few studies have examined the minimizing dead space in breathing tubing. This study investigated one-way valves in the breathing tubing during spontaneous breathing in piglets. Six female piglets aged 68-71 days spontaneously breathed sevoflurane for 4 h randomly via traditional or anti-rebreathing tubing. Arterial carbon dioxide tension (paCO₂) and respiratory characteristics were used to assess spontaneous breathing efficiency. mRNA-based methods, immunohistochemistry, and histology were used to assess the lungs. After induction, all piglets had mild hypercapnia. Those who breathed via traditional tubing experienced severe hypercapnia and required assisted ventilation (mean [95% confidence interval for mean]: 3 [0.5; 5.5] times) over 4 h. Piglets who breathed via anti-rebreathing tubing were able to normalize without assisted ventilation in less than 3 h and maintained. paCO₂ was higher in the traditional group than the anti-rebreathing group at 3 and 4 hours (46.3 [42.1; 50.5] vs. 38.3 [34.1; 42.5] mmHg, p = 0.020; 46.3 [42.6; 50.0] vs. 40.7 [37.0; 44.4] mmHg, p = 0.040). However, one-way valves increased resistance to breathing. For the lungs, mRNA-based methods indicated higher expressions of cyclin-dependent kinase, cell division cycle 20, and cyclin B2 in the traditional group; immunohistochemistry identified higher expression of phosphorylated histone 2AX in the traditional group; histology showed similar damage between the groups. These findings suggest that one-way valves inside breathing tubing reduced dead space during spontaneous breathing and enhanced inhalation anesthesia advantages in the circle breathing system.