A medical gas is defined as one that is manufactured, packaged, and intended for administration to a patient in
Medical gases are used within hospital settings for many purposes. They include the following elements and compounds:
- Oxygen, used to provide supplemental oxygen to the respiratory system; in dentistry in combination with nitrous oxide; and as an emergency standby.
- Nitrous oxide, used as an anesthetic agent in surgery; mixed with oxygen to help patients relax during dental procedures; and in cryosurgery (the use of extreme cold to destroy tissue).
- Nitrogen, used to provide pneumatic pressure in medical equipment; to prevent combustion and other chemical reactions; and as a component of many gas mixtures.
- Carbon dioxide, used to inflate areas of the body for "keyhole" surgery (small incisions made to accommodate surgical instruments); mixed with air or oxygen to stimulate breathing; and in cryosurgery or testing tooth sensitivity in dentistry.
- Medical air, used in administering breathing treatments and as a mixing component for other respiratory gases.
- Helium, used in breathing mixtures for patients with impaired lung functions.
Since medical gases are the most frequently administered drugs in the United States, the FDA is attempting to heighten both consumer and industry awareness about this specialized category of regulated products. Such related delivery hardware as regulators and tubing is also regulated as medical devices.
For the transport and delivery of a cylinder of compressed gas to a provider, the cylinder must have designated markings permanently affixed to its neck to identify the regulatory body governing the use of the cylinder; the service pressure; the serial number; the date of manufacture; the last test date; a stick-on label identifying its contents; its hazard class and color code (green for oxygen, blue for nitrous oxide, yellow for air). The cylinder is equipped with a valve threaded into it that is specifically designed only for the specific type of medical gas the cylinder is designated to contain.
Pin index safety system
The pin index safety system is used to prevent a cylinder of compressed gas from being filled with the wrong gas, or to prevent the connection of the wrong cylinder to a yoke on an anesthesia machine or to a pipeline within an institution. This system consists of three holes drilled in the valve of the gas cylinder that mate with matching pins on the yoke of the pipeline or anesthesia machine. The large central opening is the gas outlet of the cylinder. The other two holes are drilled to comply with the specifications of the safety system for the gas the cylinder is designed to contain. Despite the design of the safety system, it is not completely proof against mixups. Incidents have been reported of hospital personnel removing an oxygen fitting from an empty vessel, installing it on a nitrogen vessel and attaching it to the oxygen supply system in an institution. Patient deaths have been reported as resulting from such incidents.
Safety of hospital employees
In addition to concerns about patient safety, medical gases pose safety hazards to hospital personnel as well. The National Safety Council (NSC) has stated that hospital employees are 41% more likely to lose time from work because of injury or illness than employees in other fields. Hospital employees who work in or around laboratories or operating rooms are more likely to be injured by exposure to medical gases than workers in other areas. The highest risks are related to waste anesthetic gases, which result from inadequate maintenance of anesthesia machines or from poor work practices during the administration of anesthesia. The symptoms of acute exposure to waste anesthetic gases include drowsiness, depression, headaches, nausea, irritability, and loss of coordination. Chronic exposure can result in liver or kidney disease, cancer, or miscarriage.
Compressed medical gas—Any liquefied or vaporized gas alone or in combination with other gases.
Cryogenic vessel—A metal container designed to hold liquefied compressed medical gases at extremely low temperatures.
Cylinder—A metal container designed to hold compressed medical gases at a high pressure.
Manifold—A pipe or chamber with several openings for funneling the flow of liquids or gases.
Regulator—A mechanism that controls the flow of a medical gas.
Storage and transport of liquid oxygen
Pipelines serve as a convenient and economical method for the distribution of medical gases throughout a health care institution by reducing the number of gas cylinders required. This reduction contributes to the cleanliness of the facility, simplifies gas delivery, decreases the cost of the gas, and serves to decrease the number of personnel injuries related to the movement of heavy gas tanks. Liquid oxygen, stored at a temperature between -230– -283°F (-150°– -175°C) in double-walled stainless steel containers built to withstand a pressure of 250 lb per square inch gauge (psig), is the system used by most health care facilities for the main supply of this gas. Since liquid oxygen can vaporize rapidly with an abrupt rise in temperature to create dangerously high pressure, the bulk oxygen container must be located away from the institution for safety reasons. An underground pipeline, fitted with protective casings in areas of high surface loads, is used to transport the oxygen to the main facility's distribution system. Alarm systems are used to monitor the condition and operation of the liquid oxygen container. To avoid misfillings of oxygen containers, hose connections must be noninterchangeable. A high-pressure cylinder manifold system with an automatic switch-over valve serves as a reserve supply of liquid oxygen.
Storage and transport of liquid nitrous oxide
Cylinders of liquefied nitrous oxide connected to a gas manifold usually serve as the supply of this medical gas for facilities. The manifold controls the release of nitrous oxide from each tank. The gas is reduced to a working pressure of 45–55 psig before entering the main pipeline. Like liquid oxygen, liquid nitrous oxide has an automatic switch-over valve for a reserve bank of cylinders. These banks of gas cylinders are located in a designated storage room, which is usually adjacent to the facility's loading dock. To prevent cross-filling of tanks or rupture of the pipeline, a system of check valves, shutoff valves and pressure relief valves is employed.
Installation and inspection specifications
Pipelines in health care facilities must be constructed from hard-drawn seamless medical gas type tubing. All pipelines delivered to these facilities must also be cleaned for oxygen service, permanently labeled, and capped. Supports for the pipelines must have a copper finish if the support is to make contact with the copper tubing. Only qualified technicians should undertake all welding of medical pipelines. Shutoff valves are required throughout a facility's pipeline system; in particular, those that service a patient area should also have a pressure gauge. A newly installed pipeline system must be cleaned in accordance with set regulations before it is tested. The NFPA requires that both the installer and the user corroborate the findings of the pipeline testing before it is used with patients; and a record of these test results must be kept on file by the facility. Although this testing is designed to ensure the medical gas pipeline system is safe for patients, regulations addressing the requirements for the companies that perform the testing and the certification of pipeline systems have not been established. The American Hospital Association, however, does provide recommendations and verifications for the choice of a company to perform the inspection.
Noninterchangeable outlets for medical gases located in operating rooms may be placed on the ceilings or walls. Each one must be color-coded and labeled with the name or chemical symbol of the medical gas it delivers. Automatic closing mechanisms in the outlet of each pipeline will prevent the leakage of gas when the mating end of the transfer hose is absent. The end of each hose used to connect the pipelines to an anesthesia machine must be color-coded and provided with a gas-specific noninterchangeable connection. Three gas sources supply an anesthesia machine:
- a storage container of liquid oxygen backed up by a reserve supply of oxygen in a cylinder
- liquid nitrous oxide in a cylinder
- medical air, supplied by gas cylinders or generated on site by compressors
States regulate and enforce building codes regarding these pipelines but the variability of these codes are extreme. Some states have separate codes for each county or even for different regions within a large city. The NFPA has updated standards for the pipelines of health care facilities. In addition, the American Welding Society, the Manufacturers' Standardization Society of the Valve and Fittings Industry, the American Society of Mechanical Engineers, and the American National Standard Institute (ANSI) all have set standards for their installation, design and testing. With such varied coding, an enforcement mechanism is quite difficult. National standardization may come about only through the issue of medical liability.
Written procedures must be established for the testing intervals and maintenance of the pipelines as well as policies indicating procedures to be instituted for a shutdown. The American Hospital Association and the NFPA should be contacted regarding maintenance recommendations. The tests and procedures performed by the pipeline installer include:
- Pressurizing the pipeline to 1.5 times the working pressure for 24 hours, with each joint being checked for leaks.
- Blowing out the pipelines with oil-free nitrogen, pressurizing the pipelines to 1.2 times the working pressure for 24 hours and rechecking for leaks.
- Placing a white cloth over the outlets of the pipeline and intermittently purging it until the cloth is no longer discolored.
- Checking each pipeline with nitrogen and every outlet for the delivery of the labeled gas.
System users must repeat most of these tests and continue to ensure that each outlet is delivering the labeled medical gas. Further inspections of the manifolds, medical air compressors and alarms should be routinely performed. FDA inspectors are mandated to inspect gas liquefaction and container plants every other year.
Health care team roles
Biomedical technicians are the primary caretakers of medical gas pipelines within a health care facility. They are usually responsible for accepting medical gas deliveries and validating the contents of the delivery as well as its date and source. They should conduct scheduled shutdowns; establish protocol; maintain written policies and procedures; and remain informed of new standardized recommendations within the medical gas supply industry. They must also ensure that persons working under them have the proper training to identify medical gas cylinders, connection valves, regulators, and the distribution system within a facility.
Respiratory therapists primarily utilize oxygen from outlets within patient areas or from individual cylinders. They are responsible for checking the labels on any cylinders they use. They should also be aware of their duties in the event of a shutdown.
Certified registered nurse anesthetists and anesthesiologists should be aware of the location of the banks of gas cylinders and know the personnel responsible for changing them. They should also be knowledgeable about the workings of the cylinder bank and be able to troubleshoot the system with the biomedical technicians. Lastly, they should know the symptoms of exposure to waste anesthetic gases and the proper methods of treatment.
All employees handling medical gases should be alerted to the possible hazards associated with their use. These personnel should be trained to recognize the various medical gas labels and to examine all labels carefully. Personnel who receive medical gas deliveries should be trained to store medical grade products separately from industrial grade products. The storage area for these medical grade products should be well defined, with one area for receiving full cryogenic vessels and another area for storing empty vessels. All personnel responsible for changing or installing cryogenic vessels must be trained to connect medical gas vessels properly. They must understand how vessels are connected to the oxygen supply system and be alerted to the serious consequences of altering the connections. Emphasis must be placed on the fact that the fittings on these vessels should not be changed under any circumstances. If a cryogenic vessel fitting does not form a good connection with the oxygen supply system fitting, the supplier should be contacted immediately. The vessel should be returned to them for correction of the problem. Finally, before the medical gas is introduced into the system, a knowledgeable person should ensure that the correct vessel has been connected properly. Every opportunity should be taken to promote the importance of properly handling medical gases to all personnel and especially those who are directly involved with handling them.
Food and Drug Administration. 5630 Fishers Lane, Room 1061, Rockville, MD 20852. <http://www.fda.gov>.
National Fire Protection Association (NFPA). 1 Batterymarch Park, Quincy, MA 02269-9101. (617) 770-3000 or (800) 344-3555. Fax: (617) 770-0700. <http://www.nfpa.org>.
FDA Public Health Advisory. Guidance for Hospitals, Nursing Homes, and Other Health Care Facilities. March 2001.
Occupational Safety and Health Administration (OSHA). OSHA Technical Manual, Section VI, Chapter 1, "Hospital Investigations: Health Hazards." Washington, DC: United States Department of Labor, 2001.
United States Food and Drug Administration. <http://www.fda.gov/cder/dmpq/freshair.htm>.
Linda K. Bennington, CNS
Table Of Contents
- Cylinder markings
- Pin index safety system
- Safety of hospital employees
- KEY TERMS
- Storage and transport of liquid oxygen
- Storage and transport of liquid nitrous oxide
- Installation and inspection specifications
- Operating rooms
- Building codes
- Health care team roles