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

Abstract

Fluid mechanics show that high-density gases need more energy while flowing through a tube. Thus, highdensity 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/m 3 ) 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 N 2 O), 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/m 3 to 1.70 kg/m 3 , 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.

Endotracheal tube, by the venturi effect, reduces the efficacy of increasing inlet pressure in improving pendelluft

“…Till date, appropriate ventilatory support has been shown to have a lung protective effect [1,2,36,44]. Therefore, we should recognize ETT as an external resistance [45][46][47][48][49] and should identify the resistive component from the total respiratory work [50][51][52][53][54][55]. Fig 4C represents the gas flow from the non-dependent toward the dependent lung under the solid-like effort condition, that is, the pendelluft.…”

Effectiveness of substantial shortening of the endotracheal tube for decreasing airway resistance and increasing tidal volume during pressure-controlled ventilation in pediatric patients: a prospective observational study

“…After receiving approval from the Ethics Committee of Tohoku University Graduate School of Medicine (Ethics Committee Approval Number 2020-1-727), this single center prospective observational study was performed between November 2020 and January 2021 at Tohoku University Hospital. Some of the participants were also included in the prior published study [10]. The conceptualization, data acquisition, and analysis of this study were independently performed.…”