Effect of fit of non-rebreathing oxygen mask with a reservoir bag at various oxygen flow rates on inspiratory oxygen concentrations using a high-fidelity patient simulator

Abstract

Objectives: We investigated the effect of oxygen flow rates and fitting conditions of the non-rebreathing oxygen mask with a reservoir bag (RM) on the F_IO₂ using a high-fidelity patient simulator (HPS). Methods: We utilized an adult standard male model of the HPS (minute ventilation=9.8 l/min). After 10 min of spontaneous breathing with room air, oxygen was administered at flow rates of 6, 8, 10, 12, and 15 l/min with a loosely fitted RM, a gently fitted RM, and a tightly fitted RM. Measurements of the partial pressure of oxygen detected in simulated alveoli (P_AO₂) were recorded every 5 min following the changes in the oxygen delivery flow rate. The F_IO₂ was calculated using the following formula: P_AO₂=760 (atmospheric pressure)× F_IO₂-partial pressure of alveolar carbon dioxide (P_ACO₂). The percentage of air in inspired gas was calculated at each measuring point. Results: The F_IO₂ with a loosely fitted RM, a gently fitted RM, and a tightly fitted RM reached 0.64, 0.85, and 0.90, respectively, at an oxygen flow rate of 15 l/min. For the tightly fitted mask, the percentages of air in inspired gas was 52, 39, 30, 22, and 13, and the F_IO₂ was 0.59, 0.69, 0.76, 0.83, and 0.90 at oxygen flow rates of 6, 8, 10, 12, and 15 l/min, respectively. Conclusion: With respect to the respiratory conditions of a simulated standard adult model, the F_IO₂ was obtained at the expected level with the tightly fitted RM. However, the F_IO₂ decreased and the inspiratory resistance increased at low oxygen flow rates with a tightly fitted RM. A decrease in the F_IO₂ was significant at any oxygen flow rate with a loosely fitted RM. Therefore, oxygen flow rates should not be lowered at any fitting conditions of a RM.