INTRODUCTION: Nasal cannulas are commonly used to deliver oxygen in acute and chronic care settings; however, there are few data available on delivered fraction of inspired oxygen (FIO2). The purposes of this study were to determine the delivered FIO2 on human subjects using low-flow and high-flow nasal cannulas, and to determine the effects of mouth-closed and mouth-open breathing on FIO2. METHODS: We measured the pharyngeal FIO2 delivered by adult nasal cannulas at 1-6 L/min and high-flow nasal cannulas at 6-15 L/min consecutively in 10 normal subjects. Oxygen was initiated at 1 L/min, with the subject at rest, followed by a period of rapid breathing. Gas samples were aspirated from a nasal catheter positioned with the tip behind the uvula. This process was repeated at each liter flow. Mean, standard deviation, and range were calculated at each liter flow. F IO2 during mouth-open and mouth-closed breathing were compared using the dependent t test for paired values, to determine if there were significant differences. RESULTS: The mean resting FIO2 ranged from 0.26-0.54 at 1-6 L/min to 0.54-0.75 at 6-15 L/min. During rapid breathing the mean F IO2 ranged from 0.24-0.45 at 1-6 L/min to 0.49-0.72 at 6-15 L/min. The mean FIO2 increased with increasing flow rates. The standard deviation (± 0.04-0.15) and range were large, and FIO2 varied widely within and between subjects. FIO2 during mouth-open breathing was significantly (p < 0.05) greater than that during mouth-closed breathing. CONCLUSIONS: FIO2 increased with increasing flow. Subjects who breathed with their mouths open attained a significantly higher FIO2, compared to those who breathed with their mouths closed.
|Number of pages
|Published - May 2005
- Delivered oxygen concentration
- Nasal cannula
ASJC Scopus subject areas
- Pulmonary and Respiratory Medicine
- Critical Care and Intensive Care Medicine