This article requires a subscription to view the full text. If you have a subscription you may use the login form below to view the article. Access to this article can also be purchased.
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. FIO2 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 FIO2 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.
- Correspondence: Richard B Wettstein RRT, Department of Respiratory Care, The University of Texas Health Science Center at San Antonio, Mail Code 6248, 7703 Floyd Curl Drive, San Antonio TX 78229–3900. E-mail: .
Richard B Wettstein RRT presented a version of this report at the Open Forum of the 49th International Respiratory Congress of the American Association for Respiratory Care, held December 8–11, 2003, in Las Vegas, Nevada.
- Copyright © 2005 by Daedalus Enterprises Inc.