Fraction of Inspired Oxygen With Low-Flow Versus High-Flow Devices: A Simulation Study

Abstract

Purpose: The fraction of inspired oxygen while administering oxygen to patients must be measured as it represents the alveolar oxygen concentration, which is important from a respiratory physiology viewpoint. Therefore, the purpose of this study was to compare the fractions of inspired oxygen obtained through different oxygen delivery devices. Methods: A simulation model of spontaneous respiration was used. The fractions of inspired oxygen obtained through low- and high-flow nasal cannulas and a simple oxygen mask were measured. The fraction of inspired air was measured every second for 30 s after 120 s of oxygen administration. This was measured three times under each condition. Results: With a low-flow nasal cannula, airflow reduced both the intratracheal fraction of inspired oxygen and extraoral oxygen concentration, indicating that exhalatory respiration occurred during rebreathing and may be involved in increasing the intratracheal fraction of inspired oxygen. Conclusion: Oxygen administration during expiratory flow may lead to an increased oxygen concentration in the anatomical dead space, which may be involved in the increase in the fraction of inspired oxygen. With a high-flow nasal cannula, a high fraction of inspired oxygen can be achieved even at a flow rate of 10 L/min. When determining the optimum amount of oxygen, it is necessary to set an appropriate flow rate for patients and specific conditions without being bound by the fraction of inspired oxygen values alone. It might be difficult to estimate the fraction of inspired oxygen while using a low-flow nasal cannula and simple oxygen mask in clinical situations.

Leucocyte and platelet activation in cardiac surgery patients with and without lung injury: A prospective cohort study

“…Secondly, the preoperative flow cytometric differences in the 2 P/F ratio groups are not necessarily aetiologic factors in the development of pulmonary complications. They could also be mediators associated with other preoperatively present comorbidities, such as impaired left ventricular function, previous coronary artery disease, chronic heart failure, arteriosclerosis and atrial fibrillation, all of which are well-known risk factors for the development of acute lung injury and unfavourable outcomes after cardiac surgery [ 26 ] and all of which are associated with increased inflammatory status, platelet activation and endothelial-driven hypercoagulability [ 27–30 ]. In our study, these risk factors were more common in patients in the low P/F group.…”

“…To determine surgery-related lung injury, we used, analogous to these Berlin criteria, a maximum time period of 1 week after surgery. The FiO 2 is notoriously unreliable from the moment low-flow oxygen supply is initiated [ 27 , 28 ], and the PaO 2 is only measured when clinically indicated when the patient is in the general thoracic surgery ward. Therefore, the P/F ratio was not available for extubated patients.…”