Compressed Gas Systems

Many years ago, a physician said to me that when a biomed gets a trouble call on a device or system, he/she becomes the world’s expert on that device or system in the eyes of the person making the call—even if the biomed has never seen the problem before. That is still a true statement, but most of you are not surprised as often as in the past. One area that can surprise many BMETs is the compressed gas system in hospitals. Generally, the BMET is called when others have not responded and the caregivers are getting concerned, so here we go again doing someone else’s job.

In most hospitals, there are connections for suction and oxygen at almost all bed and treatment locations. In certain areas of the hospital, compressed air is also present. In some specialty areas, nitrogen and nitrous oxide may also be present. The good thing is that each of these gases has a distinct fitting and cross connections are very difficult to get, but they can happen. Never discount the ingenuity of an intern or nurse when it comes to connections, as they can be very creative. Many of you probably have stories that you can tell on some of the more amazing connections that you have had to unravel.

To the Basics

Both air and oxygen, at the wall outlet, should be at 50 PSIG and should not dip more than 5 PSIG, even if every outlet on the floor is in use. As part of your rounds, take a look at the gages on each floor, at the shutoff panel on each floor—usually near the nurses’ station—to be sure that the pressures are correct. The flow rates can vary from hospital to hospital, but a minimum of 5.0 standard cubic feet per minute (SCFM)—about 18 liters per minute (LPM)—should be present. Also, you should note any outlets that are leaking; they may have caps on them or flow meters at off positions. They should be repaired, but that may take years in some hospitals. This is not a high priority because the floor gas service would have to be shut down to do the work. If the outlet is leaking nitrogen or nitrous oxide, it should be fixed quickly. Nitrogen leaks are a cost factor and should be addressed quickly, but often are not as getting to pipes can be difficult. Nitrous oxide, sometimes called laughing gas, poses a health hazard as it makes people not care and it will explode if the levels get too high.

Nitrogen pressure ranges from 100 to 150 PSIG while nitrous oxide is in the 40 to 50 PSIG range, again with no more than a 5 PSIG variance.

Two points to remember: PSIG means pounds per square inch gage. For some reason, some vendors are giving pressures in bars, which must be to see if we can keep up. A bar is 15 PSIG, unless you are out having a “milkshake” or two, then it means what you think it means.

In most hospitals, the oxygen is delivered in liquid form and is vaporized off as needed by the draw on the system. No BMET should do anything with the tanks except call the vendor if there is a problem. You can get hurt if something goes wrong with the tank and you try to fix it—call the vendor!

Flow Rates and Testing

Compressed air is generally made at the hospital, and the common problems include water in the pipes, particulate matter, smells, and low flows. These are all related and while not generally our problem, they become our problems when the ventilator’s filters block up. Where air intake is located is often a problem, when the hospital was built that followed the requirements of NFPA or the Compressed Gas Association. Over the years, renovations may have put vehicles next to the intake, or vegetation, or in one case the lawn sprinkler, which was showering the intake and it took a while to figure out why the compressed air was wet.

The typical flow rates for oxygen and air are measured in SCFM, or LPM. Get one flowmeter and keep it as your test meter so you always have a reference. Also, once per year compare it with another meter to be sure that it is still working well. This is also important to do with the pressure gages.

Vacuum testing should be done on a schedule that is agreeable with both the facilities and nursing departments. During your rounds you should look for vacuum outlets that have a piece of thick paper on them. This is the simple way to stop them from whistling when they are leaking. These should be put on the list in the facilities department for repair.

Many people just look at the level of suction measured in inches of mercury with 25 being the ideal number. You will rarely see suction levels above 23.5 inches. The level is not as important as the flow rate. Flow rates should be above 35 LPM or 8.75 SCFM to be effective in clearing airways. Many people do not test the flow rate, and that is the most important test. A good demo on why the flow rate is important is the following: Open a can of cream of mushroom soup, turn on the suction, and put a number 18 catheter in the soup. The gage will go up to 22 or more, but no soup will be moving until the flow rate is increased to more than 15 liters per minute.

As a reminder, tanks are still used in many hospitals, so get to know the common colors of the tanks: green for oxygen, blue for nitrous oxide, yellow for medical air, and black for nitrogen. These are the same colors for the pressure hoses, with white being for vacuum. Look for hoses being used on gases that should not be, and get them out of service. This is a common problem in operating rooms where the anesthesia techs are also very creative.

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David Harrington, PhD, is a health care consultant, Medway, Mass, and is a member of 24×7‘s editorial advisory board. Eric Massey is a BMET with Technology in Medicine, Day Kimball Hospital, Putman Conn. For more information, contact .