Prevention of Airway Fires: Do Not Overlook the Expired Oxygen Concentration

Remz, Matthew; Luria, Isaac BS; Gravenstein, Michael; Rice, Scott D.; Morey, Timothy E. MD; Gravenstein, Nikolaus; Rice, Mark J. MD

doi: 10.1213/ANE.0b013e318298a692
Patient Safety: Research Report

BACKGROUND: It is generally accepted that when an ignition source is used the inspired oxygen concentration (FIO2) should be <30% in the breathing circuit to help prevent airway fires. The time and conditions required to reduce a high O2% in the breathing circuit to <30% has not yet been systematically studied.

METHODS: We evaluated the inspired and expired circuit oxygen concentration response times of an Aestiva Avance S/5 anesthesia machine to reach an FIO2 of <30% from a starting FIO2 of 100% and 60% after reducing the FIO2 to 21%. The circuit was connected to a human patient simulator which has a functional residual capacity of 2 L, total lung capacity of 2.8 L, an oxygen consumption of 200 mL/min, and respiratory quotient of 0.8. Fresh gas flow (FGF) inputs of 2 L/min and 5 L/min were chosen to represent a spectrum of typical clinical FGF rates. Minute ventilation was set at 4 L/min. Determining the requisite median time to reach an O2 concentration of <30% in the breathing circuit was the primary aim of the study.

RESULTS: The median times (1st–99th percent confidence interval) required to achieve inspiratory and expiratory oxygen concentrations of <30% with the extended circuit configuration when starting at 60% for 5 L FGFs were 35 (32–36) and 104 (88–122) seconds, respectively. With 2 L FGF, these median times increased to 303 (291–313) and 255 (232–278) seconds, respectively. A shortened circuit configuration (P = 0.006) and higher FGF flow rate (P < 0.0001) were noted to be factors decreasing the median time required to achieve an oxygen concentration of <30%.

CONCLUSIONS: Both inspired and expired circuit oxygen concentration may take minutes to decrease to <30% depending on circuit length, FGF rate, and starting circuit oxygen concentration. During the reduction in FIO2, the expiratory oxygen concentration may be >30% for a considerable time after the FIO2 is in a “safe” range. An increased expired oxygen concentration should also be considered an airway fire risk, and patient care protocols may need to be modified based on future studies.

Published ahead of print July 8, 2013

From the Department of Anesthesiology, University of Florida College of Medicine, Gainesville, Florida.

Accepted for publication April 15, 2013.

Published ahead of print July 8, 2013

Funding: Department of Anesthesiology, University of Florida College of Medicine, Gainesville, Florida.

The authors declare no conflicts of interest.

This report was previously presented, in part, at the 2011 American Society of Anesthesiologists meeting in Chicago, IL

Reprints will not be available from the authors.

Address correspondence to Mark J. Rice, MD, Department of Anesthesiology, University of Florida College of Medicine, PO Box 100254 Gainesville, FL 32610. Address e-mail to mrice@anest.ufl.edu.

© 2013 International Anesthesia Research Society