Tohoku J. Exp. Med., 2022 April, 256(4)

Influence of Respiratory Gas Density on Tidal Volume during Mechanical Ventilation: A Laboratory Investigation and Observational Study in Children

Kazuhiro Takahashi,1 Hiroaki Toyama,1 Yutaro Funahashi,1 Shin Kawana,2 Yutaka Ejima,3 Kenji Kikuchi,4 Takuji Ishikawa5 and Masanori Yamauchi1

1Department of Anesthesiology and Perioperative Medicine, Tohoku University Graduate School of Medicine, Sendai, Miyagi, Japan
2Department of Anesthesiology, Miyagi Children's Hospital, Sendai, Miyagi, Japan
3Division of Surgical Center and Supply, Sterilization, Tohoku University Hospital, Sendai, Miyagi, Japan
4Department of Finemechanics, Graduate School of Engineering, Tohoku University, Sendai, Miyagi, Japan
5Graduate School of Biomedical Engineering, Tohoku University, Sendai, Miyagi, Japan

Fluid mechanics show that high-density gases need more energy while flowing through a tube. Thus, high-density anesthetic gases consume more energy to flow and less energy for lung inflation during general anesthesia. However, its impact has not been studied. Therefore, this study aimed to investigate the effects of high-density anesthetic gases on tidal volume in laboratory and clinical settings. In the laboratory study, a test lung was ventilated at the same pressure-controlled ventilation with 22 different gas compositions (density range, 1.22-2.27 kg/m3) using an anesthesia machine. A pneumotachometer was used to record the tidal volume of the test lung and the respiratory gas composition; it showed that the tidal volume of the test lung decreased as the respiratory gas density increased. In the clinical study, the change in tidal volume per body weight, accompanied by gas composition change (2% sevoflurane in oxygen and with 0-30-60% of N2O), was recorded in 30 pediatric patients. The median tidal volume per body weight decreased by 10% when the respiratory gas density increased from 1.41 kg/m3 to 1.70 kg/m3, indicating a significant between-group difference (P < 0.0001). In both settings, an increase in respiratory gas density decreased the tidal volume during pressure-controlled ventilation, which could be explained by the fluid dynamics theory. This study clarified the detailed mechanism of high-density anesthetic gas reduced the tidal volume during mechanical ventilation and revealed that this phenomenon occurs during pediatric anesthesia, which facilitates further understanding of the mechanics of ventilation during anesthesia practice and respiratory physiology.

Keywords —— airway resistance; anesthetic gas density; energy of gas; respiratory mechanism; tidal volume

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Tohoku J. Exp. Med 2022, 256, 271-281.

Correspondence: Hiroaki Toyama, M.D., Ph.D., Department of Anesthesiology and Perioperative Medicine, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Aoba-ku, Sendai, Miyagi 980-8574, Japan.

e-mail: h-toyama@umin.ac.jp