Circulation 94,429 • Volume 27, No. 1 • Summer-Spring 2012   Issue PDF

Converting an Anesthesia Circuit to Deliver and Titrate Supplemental Oxygen

Alec Rooke, PhD, MD

To the Editor

I read with great interest the recent lead article on fire safety in the OR,1 particularly the circumstances where a loose face mask is desired to provide supplemental oxygen. The algorithm recommends the use of a blender to provide oxygen at 30% or less. However, it is relatively simple to provide an air/oxygen mixture to a standard face mask if connected to the circuit of an anesthesia machine by large diameter tubing. Large diameter tubing is needed because the small diameter tubing from the standard face mask creates high resistance in the circuit with subsequent high pressure and activation of the continuing pressure alarm (Figure 1).


We use a standard face mask (with the small diameter tubing removed) or an aerosol face mask attached to the circle system by large diameter extension tubing (Figure 2). This arrangement keeps the system pressure low and permits high gas flow at any FiO2. The high flow rate helps disburse the exhaled gas and minimizes re-breathing, and a low FiO2 avoids oxygen trapping. When using the circuit in this fashion to provide an air: oxygen mixture, the APL must be closed in order to prevent the fresh gas from shunting to the scavenge system.

When possible, room air is preferable for minimizing on-patient fires; however, this device should allow titration of FiO2 to the lowest possible concentration when supplemental oxygen is required.

G. Alec Rooke, MD, PhD
Professor, Anesthesiology and Pain Medicine
University of Washington, Seattle, WA


  1. Stoelting RK, Feldman JM, Cowles, CD, Bruley ME. Surgical fire injuries continue to occur: Prevention may require more cautious use of oxygen. APSF Newsletter 2012;26(3):41,43.