Effect of net gas volume changes on alveolar and arterial gas partial pressures in the presence of ventilation-perfusion mismatch

Abstract

The second gas effect (SGE) occurs when nitrous oxide enhances the uptake of volatile anesthetics administered simultaneously. Recent work shows that the SGE is greater in blood than in the gas phase, that this is due to ventilation-perfusion mismatch, that as mismatch increases, the SGE increases in blood but is diminished in the gas phase, and that these effects persist well into the period of nitrous oxide maintenance anesthesia. These modifications of the SGE are most pronounced with the low soluble agents in current use. We investigate further the effect of net gas volume loss during nitrous oxide uptake on low concentrations of other gases present using partial pressure-solubility diagrams. The steady-state equations of gas exchange were solved assuming a log-normal distribution of ventilation-perfusion ratios using Lebesgue-Stieltjes integration. It was shown that under these conditions the classical partial pressure-solubility diagram must be modified, that for currently used volatile anesthetic agents the alveolar-arterial partial pressure difference is less than that predicted in the past, and that the alveolar-arterial partial pressure difference may even be reversed during uptake in the case of highly insoluble gases such as sulfur hexafluoride. Comparing this with the situation described previously for nitrogen in steady-state air breathing, we show that for nitrogen, the direction of the alveolar-arterial gradient is opposite to the direction of net gas volume movement. Although gas uptake with ventilation-perfusion inequality exceeding that when matching is optimal is shown to be possible, it is less likely than alveolar-arterial partial pressure reversal. NEW & NOTEWORTHY Net uptake of gases administered with nitrous oxide may proceed against an alveolar-arterial partial pressure gradient. The alveolar-arterial gradient for nitrogen in the steady-state breathing air depends not only on the existence of a distribution of ventilation-perfusion ratios in the lung but also on the presence of a net change in gas volume and is opposite in direction to the direction of net gas volume uptake.

Effects of salbutamol on the kinetics of sevoflurane and the occurrence of early postoperative pulmonary complications in patients with mild-to-moderate chronic obstructive pulmonary disease: A randomized controlled study

“…The present results conformed to those of the previous studies [ 13 , 14 ]. In 2014, a study conducted by da Costa et al [ 21 ] demonstrated that the effects of bronchodilation were greater in patients in the initial stage of COPD than in the healthy volunteers and that the improvement in the oscillatory mechanics decreased with increasing severity of COPD, implying that the stages of COPD affected the efficacy of salbutamol.…”

“…End-tidal samples were collected from the first breaths at 1, 2, 3, 4, 5, 7, 10, and 15 min before the surgery. The concentrations of inspiratory (F I ) and expiratory (F A ) sevoflurane were recorded at the proximal end of the endotracheal tube by using an infrared gas analyzer (RGM5250, Ohmeda, BOC Health Care, Inc., Louisville, CO, USA) [ 13 , 14 ]. The analyzer was calibrated prior to use in accordance with the manufacturer’s instructions.…”

“…We speculated that the administration of salbutamol will accelerate the bulk transportation of sevoflurane, an inhalation anesthetic, to the alveoli through improved lung volume and uniform gas distribution to the lung, while simultaneously enabling the smooth elimination of sevoflurane from the lung and shortening the recovery time [2]. We also hypothesized that salbutamol would be helpful in controlling sputum expectoration and bronchial constriction via its bronchodilating effect on the airway, which eventually may decrease the occurrence of PPCs [13][14][15].…”

“…The improved lung volumes confer benefits to the ventilation status, optimize volume movement, improve uniform gas distribution, and decrease ventilation/perfusion (V/Q) mismatch. Lung ventilation is an important determinant for the transport of volatile agents to the alveolar-capillary interface and further affects the uptake of these agents into blood and the brain [ 13 , 14 ]. We speculated that the administration of salbutamol will accelerate the bulk transportation of sevoflurane, an inhalation anesthetic, to the alveoli through improved lung volume and uniform gas distribution to the lung, while simultaneously enabling the smooth elimination of sevoflurane from the lung and shortening the recovery time [ 2 ].…”

Effects of N2O elimination on the elimination of second gases in a two‐step mathematical model of heterogeneous gas exchange

“…All programs were written in MATLAB. Further details of our technique are discussed elsewhere (Korman et al, 2018(Korman et al, , 2019(Korman et al, , 2020. The relationships used to generate the equations and figures are discussed further in Appendix 3.…”