Determination of the Minimal Fresh Gas Flow to Maintain a Therapeutic Inspired Oxygen Concentration in a Semi-Closed Anesthesia Circle System Using an Oxygen Concentrator as the Oxygen Source

摘要

The purpose of this study was to determine the rate of oxygen dilution, resulting from argon accumulation, using 3 low fresh gas flow rates using an oxygen concentrator in a semi-closed anesthesia circle system. This was a prospective, non-experimental descriptive designed study. Nine subjects participated in 3 trials each of fresh gas flows (0.5 liter, 1 liter, and 2 liters) from the oxygen concentrator, with the order counterbalanced, for a total of 27 trials. Preoxygenation and denitrogenation were done prior to the trial beginning. Inspiratory and expiratory gases were measured directly for oxygen, carbon dioxide, and nitrogen; and indirectly for argon. The expiratory gases passed through a carbon dioxide absorber in the circle system prior to entering the inspiratory limb. Continuous monitoring of inspiratory and expiratory gas concentrations was done, including 5 minute recordings. Continuous monitoring of oxygen saturation,respiratory status, and electrocardiogram was done, with 10 minute recordings including blood pressure. A one-way repeated measures ANOVA was used to determine the differences of the inspired oxygen concentration at baseline, 15 minutes, and 30 minutes between subjects for the 3 different flow rates. Data analysis showed a statistically significant difference in inspired oxygen concentration between 0.5 and 1 liter per minute, and between 0.5 and 2 liters per minute. There was not a significant difference between 1 and 2 liters per minute. A statistically significant difference across all three flow rates in inspired concentrations of oxygen (p <0.0001), argon (p <0.0001), and nitrogen (p <0.0001) were seen. There is a statistically and clinically significant increase in oxygen dilution, and argon and nitrogen accumulation at the low flow rate of 0.5 liter per minute.