Influence of Respiratory Gas Density on Tidal Volume During Pressure-Controlled Ventilation: A Laboratory Investigation and Observational Study in Children.

Fluid mechanics shows that high-density gases need more energy while flowing through a endo-tracheal tube. This means that during general anesthesia, high-density gases left less energy for lung inflation under pressure-controlled ventilation (PCV). However, the impact have not been studied. This study investigated the effects of high-density anesthetic gases on tidal volume (TV) in laboratory and clinical settings.In laboratory study, a test lung was ventilated at fixed PCV with 22 different gas compositions (density range, 1.22-2.27 kg/m 3 ) using an Avance® anesthesia machine. The TV of the test lung and the respiratory gas composition were recorded by a pneumotachometer. As a result, the TV of the test lung decreased as the respiratory gas density increased. In clinical study, the change in TV/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. Median TV/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 laboratory and clinical settings , an increase in respiratory gas density decreases the TV during PCV, and it could be well explained by the theory of fluid dynamics.