As demand for anesthesia services outside the traditional O.R. environment continues to grow, the technical and logistic challenges of providing anesthesia multiply. Anesthesia providers are concerned about the space, equipment and support requirements for safe anesthesia, while proceduralists demand a full range of anesthesia services in a closet-sized space.
One of the common concerns is the need for adequate waste anesthetic scavenging in “off-site” locations. These may be small, minimally-equipped procedure or treatment rooms lacking wall oxygen, nitrous oxide or even vacuum sources. Scavenging in this situation may be difficult or impossible. What is an appropriate solution?
The history of waste anesthetic scavenging dates to the 1970s. In the late 1960s it was observed that chronic exposure to anesthetic waste gases might have negative health effects on perioperative staff, specifically an increased incidence of miscarriage in O.R. personnel.1 Multiple studies failed to find a consistent association between exposure to waste anesthetic gases and adverse health outcomes. Nonetheless, this concern led to the 1977 recommendation by the National Institute of Occupational Safety & Health (NIOSH) that anesthetic concentrations in the O.R. environment be limited. Until this time, the “exhaust” from anesthesia machines was vented into the O.R. environment with little concern. The use of higher fresh gas flows and semi-open circuits at the time also contributed to the O.R. pollution.
In the United States, the requirements surrounding permissible levels of waste anesthetic gases and proper methods to scavenge such gases are controlled by both the Occupational Safety and Health Administration (OSHA) and The Joint Commission (TJC), formerly known as The Joint Commission on Accreditation of Healthcare Organizations (JCAHO).
OSHA advises that no worker be exposed to greater than 25 parts per million (ppm) of nitrous oxide when used as a single inhalational anesthetic agent. Halogenated anesthetic agents have an exposure limit of 2 ppm when used alone. However, when halogenated anesthetic agents are used in combination with nitrous oxide, the permissible level of exposure of the halogenated agent drops to 0.5ppm. OSHA recommends that each facility should have a scavenging system that limits exposure to positive/negative pressure in the patient’s breathing circuit, a collection system to entrain overflow vapors and a ventilation system to carry waste anesthetic gases away from the O.R. Furthermore, O.R. air sampling should occur quarterly for both nitrous oxide and halogenated agents. Separately, O.R. ventilation systems should exchange an entire room’s air content at least 15 times per hour.2
TJC requires that a facility have a system in place for monitoring and disposal of hazardous gases. Furthermore, TJC requires that each facility have a scavenging system in place for waste anesthetic gases. Whereas OSHA recommends that workers not be exposed to specific amounts of anesthetic gases, TJC mandates scavenging.
This concern led to the implementation of anesthetic scavenging or waste anesthetic gas disposal (WAGD) systems for O.R.s. It generally took one of two forms: “passive” or “active.” Passive scavenging is simply the rerouting of the machine exhaust directly or indirectly outside the O.R. This classically took the form of a hose through an open window, which is still done in many underdeveloped countries. Active scavenging, on the other hand, routes the waste anesthetic into a vacuum system, a more familiar method used in the majority of modern hospitals. There is a problem with connecting the low-pressure machine exhaust directly to a vacuum source: the possibility of uncontrolled application of negative pressure to the patient breathing circuit or, less likely, the occlusion of the exhaust line, producing high resistance to exhalation. This issue has traditionally been resolved through the use of a scavenger interface, which provided both positive- and negative-pressure relief. Anesthesia machines were soon provided with external (or internal) scavenger interfaces configured for either passive or active scavenging. Passive gas scavenging interfaces are currently much less common and usually limited to office-based suites or remote locations.
In the EU and other countries, this waste anesthetic is sent to a separate, dedicated WAGD vacuum system, while in the U.S. it is commonly vented into the medical vacuum system to be exhausted outside the hospital. WAGD hose and fittings are color-coded lavender with a discrete keyed fitting, whether they are routed to medical vacuum or to a dedicated WAGD vacuum system.
In a setting with limited availability of piped medical gas/vacuum, an anesthesia machine in the U.S. may be modified to exhaust waste gas into the medical vacuum system by changing the lavender hose fitting to mate with the wall vacuum inlet (Figure 1). There are few drawbacks to this approach in the U.S. One issue has been the introduction of high-oxygen waste streams into vacuum systems powered by oil-lubricated pumps. The increased demand on older vacuum systems with consequent overload/overheating has led to some incidents of fire in oil-lubricated vacuum pumps.
The other solution to scavenging in “austere” locations is to implement some form of passive scavenging. Most anesthesia machines require modification of the scavenger interface to provide passive, low-pressure exhaust, and access to open windows is typically limited in radiology or other procedural areas. However, in the worst case, the use of ventilation intake ducts may be possible only if the ventilation (HVAC) system does not recirculate air.3 Discussion of the scavenging needs of the suite with the relevant physical plant or air conditioning engineers is important with this option. Also, in some units such as MRI, which have separate high-volume air conditioning systems, the air turnover in the suite is sufficient to limit the ambient concentrations of anesthetics to levels below standard thresholds.
In either case, the provision of adequate anesthetic scavenging is now mandatory for compliance with TJC requirements. It may be a relatively simple matter in the case where vacuum or WAGD piping is present, or rather difficult in other cases. Collaboration with hospital administration and physical plant and anesthesia support staff is essential to the safe provision of general anesthesia in these new locations.
Scavenging of waste anesthetic gases within and outside the O.R. is vitally important to the safety of the patient, perioperative personnel and the environment.4 With most anesthesia machine manufacturers providing equipment globally, it is becoming apparent that we need to be more aware of what type of scavenging system our facilities have in place. Future anesthesia equipment purchases should take into account the type of scavenging system in place at your facility.5 On the horizon, new scavenger interfaces have shown promise of decreasing vacuum pump workload and producing energy savings. Anesthetic gas recovery from the scavenging system has the potential to revolutionize our specialty’s environmental impact.
Jason S. Lane, M.D., M.P.H. is Assistant Professor of Anesthesiology and Medical Director of Remote Anesthesia Services, Department of Anesthesiology, Vanderbilt University Medical Center, Nashville.
James Michael Berry, M.D., is Professor and Division Chief, Adult Anesthesia, Vanderbilt University School of Medicine, Nashville.
1. Boivin JF. Risk of spontaneous abortion in women occupationally exposed to anaesthetic gases: a meta-analysis. Occup Environ Med. 1997;54(8):541-548.
2. Criteria for a recommended standard: occupational exposure to waste anesthetic gases and vapors. DHEW (NIOSH) Publication No. 77-140. Cincinnati, OH: U.S. Department of Health, Education and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health; 1977.
3. Annex A explanatory material: A.184.108.40.206. NFPA 99: Standard for Health Care Facilities. Quincy MA: National Fire Protection Association;140.
4. Ryan SM, Nielsen CJ. Global warming potential of inhaled anesthetics: application to clinical use. Anesth Analg. 2010;111(1):92-98.
5. Allen M. Waste Anesthetic Gas Disposal (WAGD) Systems. Charlotte, NC: BeaconMedaes; 2004.