Volume 8, No. 3 • Fall 1993

Understanding Your Machine: O2 Flush Valve Key to Safety

Clayton Petty, M.D.

Many anesthesia providers use the oxygen flush valve daily especially in those cases where the face mask fit is not optimal during the induction. When an emergency occurs it is comforting to know where a supply of oxygen is readily located, how much can be delivered, and that a flow is available despite the anesthesia being lifted on or off.

When ether and chloroform were introduced as anesthetic agents, they were delivered with air as the carrier gas. Nitrous oxide was then introduced with air and nitrous oxide as the carrier gases. Oxygen enrichment in the carrier gas was a relatively late introduction into the practice of anesthesia. However, oxygen enrichment carrier gas is now considered a critical component of any general anesthetic and is even used to supplement regional anesthesia and monitored anesthesia care.

The oxygen flush valves on anesthesia machines manufactured in the United States today have many excellent safety features:

1. Color coded

2. Labeled “02′ 3. Self-closing

4. Delivers 35-75 L/min

5. Protective rim

6. Mounted on the front of the machine for easy accessibility

7. Delivers oxygen directly into the common gas outlet without passing through a flowmeter or vaporizer

Oxygen is supplied directly to the oxygen flush valve. Figure I demonstrates the common pipeline connection of the oxygen supply from the hospital pipeline and the oxygen supplied from the oxygen compressed gas cylinder. The anesthesia machine oxygen pipeline is then divided with one branch controlled by the on/off switch of the anesthesia machine and the other branch going directly to the oxygen flush valve. As long as oxygen pressure is present in the common anesthesia machine pipeline, the oxygen flush valve can be activated with or without the main switch of the machine being on. Oxygen passes through the oxygen flush valve into the common gas outlet and directly into the patient s breathing circuit.

A typical oxygen flush valve assembly is shown in the schematic of Figure 2. The anesthesia machine pipeline pressure of 40-50 psig pushes a ball valve against a circular valve seat (Figure 2A) which stops flow of oxygen through the oxygen flush valve. When the anesthesia provider presses the flush button (Figure 2B), the pin lifts the ball valve off the valve seat and allows oxygen to flow into a common gas outlet at a rate of 35-75 L/min. When the anesthesia provider releases the flush button, the hall valve retaining spring forces the ball valve to seat and flow is stopped.

The oxygen flush button is something we certainly do not need to use on every case but its presence should give us a certain sense of security and perhaps even a little peace of mind.

Dr. Petty is Professor of Anesthesiology, Uniformed Services, University of Health Sciences, Bethesda, MD and currently Professor at the University of Utah at St. Mark’s Hospital, Salt Lake City.

Figure 1. A pipeline diagram of an oxygen flush valve. Note the direct pipeline of oxygen to the flush valve. Released oxygen bypasses the flowmeters and vaporizers and enters directly into the fresh gas common outlet. (Redrawn from Technical Services Manual. North American Drager, Telford, PA 1985.)

Figure 2. Oxygen flush value for the anesthesia machine. (A) A spring holds the ball valve against the valve seat when the oxygen flush valve is in the closed position. (B) Pushing the oxygen flush button inward forces the ball valve off the valve seat and the oxygen flows into the common gas outlet of the anesthesia machine. (Reproduced with permission from Bowie E, Huffman LM: The Anesthesia Machine Essentials for Understanding. Ohmeda. The BOC Group, Inc. 1985.)