|Commercial name||Year of
|Nitrous oxide||Nitrous oxide||1844||Yes|
It is estimated that more than 200,000 health care professionals
--including anesthesiologists, nurse anesthetists, surgical and obstetric
nurses, operating room (OR) technicians, nurses aides, surgeons,
anesthesia technicians, postanesthesia care nurses, dentists, dental
assistants, dental hygienists, veterinarians and their assistants,
emergency room staff, and radiology department personnel --are potentially
exposed to waste anesthetic gases and are at risk of occupational illness.
Over the years there have been significant improvements in the control of
anesthetic gas pollution in
Exposure measurements taken in ORs during the clinical administration
of inhaled anesthetics indicate that waste gases can escape into the room
air from various components of the anesthesia delivery system. Potential
leak sources include tank valves,
Studies of the effects of these agents in the
Unlike the situation in the OR,
Because PACU nurses must monitor vital functions in close physical proximity to the patient, they can be exposed to measurable concentrations of waste anesthetic gases. While random room samples may indicate relatively low levels of waste gases, the breathing zone of the nurses may contain higher levels.Consequently, air samples obtained within the breathing zone of a nurse providing bedside care are most likely to represent the gas concentrations actually inhaled.
In general, the detection of halogenated anesthetic agents by their odor would indicate the existence of very high levels, as these agents do not have a strong odor at low concentrations. For example, detection of high levels of halothane may be difficult for PACU nurses because one study (Hallen et al. 1970) found that fewer than 50% of the population can detect the presence of halothane until concentrations are 125 times the NIOSH REL.
In anesthetizing locations and PACUs where exposure to waste gases is
known to occur, it is important for
While mutagenicity testing of nitrous oxide (N2O) has demonstrated negative results (Baden 1980), reproductive and teratogenic studies in several animal species have raised concern about the possible effects of nitrous oxide exposure in humans. In general, studies demonstrate reproductive and developmental abnormalities in animals exposed to high concentrations ofN2O. In one study by Viera et al. (1980), spontaneous abortion was observed in rats at 1000 ppm or more. According to NIOSH (1994), similar concentrations of 1000 ppm have been found in operating rooms and in dental operatories not equipped with scavenging systems.
Smith, Gaub, and Moya (1965) reported fetal resorption in rats exposed to nitrous oxide at high doses. Fink, Shepard, and Blandau (1967) administered 45% to 50% nitrous oxide and 21% to 25% oxygen to pregnant rats for 2, 4, and 6 days starting at day 8 of gestation. Surviving fetuses from these rats demonstrated rib and vertebral defects. Corbett and colleagues (1973) also reported an increase in fetal deaths and a smaller number of offspring in rats exposed to levels ranging from 1,000 to 15,000 ppm of nitrous oxide.
There are also studies involving human subjects. A recent
retrospective study (Rowland
et al. 1992) reported that female dental assistants exposed to
unscavenged N2O for 5 or more hours per week
had a significantly increased risk of reduced fertility compared with
and colleagues (1995) examined the relationship between occupational
exposure to N2O and spontaneous abortion in
female dental assistants. Duration of exposure was a surrogate for
exposure data. Nitrous oxide exposure was divided into two separate
variables: scavenged hours (hours of exposure per week in the presence
of scavenging equipment) and unscavenged hours of exposure per week.
Women who worked with N2O at least 3 hours per
week in offices not using scavenging equipment had an increased risk of
spontaneous abortion (relative risk = 2.6, 95% confidence interval
Several summaries of the epidemiologic studies of exposure to
N2O and reviews of the topic generally
including animal and retrospective studies (Purdham
1988; and NIOSH
1994) have been published. They report a consistent excess of
spontaneous abortion in exposed women. Other summaries of the
epidemiologic studies do not establish a
Halogenated agents are used with and without
N2O and have been linked to reproductive
problems in women and developmental defects in their offspring. As early
as 1967 there were reports from the Soviet Union, Denmark, and the
United States (Vaisman
and Petersen 1970; Cohen,
Bellville, and Brown 1971) that exposure to anesthetic agents
including halothane may cause adverse pregnancy outcomes in
A number of human epidemiologic studies have been performed since the
early 1970s to assess the potential harm to reproductive health that
exposure to anesthetics might cause. Generally, these were mailed
questionnaire surveys completed by persons (usually anesthesiologists
and nurses) identified through registries. As such, the studies were
retrospective and inquired about previous reproductive outcomes for
which validation was not available. In addition, no exposure data were
available and many of the early studies predated the use of scavenging
systems. Studies documenting a statistically significant excess of
spontaneous abortions in exposed female anesthesiologists include those
of Cohen and colleagues 1971,
The evidence for an association between anesthetic exposure and congenital anomalies is less consistent. Only a few studies in some subpopulations of exposed workers found a positive association (Corbett et al. 1974; ASA 1974; Pharoah et al. 1977). Other studies reported no association with congenital anomalies (Axelsson and Rylander 1982; Lauwerys et. al. 1981; Cohen et. al. 1980; Rosenberg and Vanttinnen 1978).
The retrospective study by Cohen
and colleagues (1980) reported that female dental chairside
assistants who had experienced heavy exposure (defined as more than
eight hours per week) to waste anesthetic gases reported a significant
increase in the rate of spontaneous abortions (19.1 per 100 pregnancies)
compared with the rate in the
Another study of reproductive outcomes associated with exposure to anesthetic gases (also a questionnaire survey, conducted between 1981 and 1985) documented both a statistically significantly increased odds ratio for spontaneous abortion in exposed females (odds ratio 1.98; CI = 1.53-2.56) and spouses of exposed male workers (odds ratio 2.30; CI = 1.68-3.13), and for congenital abnormality in offspring of exposed females \ (odds ratio 2.24; CI = 1.69-2.97) and offspring of spouses of exposed male workers (odds ratio 1.46; CI = 1.04-2.05) (Guirgis et al. 1990).Duration of exposure as estimated by a hygiene investigation was used as an exposure surrogate. These findings of a positive association were surprising because scavenging systems were thought to have been more likely in use during the study period compared to many of the previously cited papers, almost a decade older.
In the mid 1970's, human studies testing the cognitive and the motor skills of male subjects/volunteers, showed that exposure to concentrations of anesthetic gas mixtures commonly found in the unscavenged operating room, resulted in decreased ability to perform complex tasks (Bruce et al. 1974, 1975, later invalidated by the author, 1983, 1991). These volunteers exhibited decrements in performance following exposures at: 500 ppm N2O in air; 500 ppm N2O plus 15 ppm halothane in air; and 500 ppm N2O plus 15 ppm enflurane in air. However, studies that attempted to replicate the results of the human performance studies that showed decrements failed to confirm these findings (Smith and Shirley 1978).
Potential harmful effects due to desflurane exposure have been
addressed in a few recent studies, including those of Holmes
and colleagues (1990), an animal study; and Weiskopf
and colleagues (1992), a study conducted with human volunteers.
However, desflurane’s potential as a hazard to
Unlike N2O, there is evidence that halothane is mutagenic in certain in vitro test systems (Garro and Phillips 1978) and that halothane is metabolized to reactive intermediates that covalently bind to cellular macromolecules, suggesting potential mechanisms of toxicity (Gandolfi et al. 1980).
Despite questions about design issues or selection bias in some studies, the weight of the evidence regarding potential health risks from exposure to anesthetic agents in unscavenged environments suggests that clinicians need to be concerned. Moreover, there is biological plausibility that adds to the concern that high levels of unscavenged waste anesthetic gases present a potential for adverse neurological effects or reproductive risk to exposed workers or developmental anomalies in their offspring (Cohen et al. 1980; Rowland 1992).
While the use of prospective studies and carefully designed research protocols is encouraged to elucidate areas of controversy, a responsible approach to worker health and safety dictates that any exposure to waste and trace gases should be kept to the lowest practical level.
An anesthesia machine is an assembly of various components and devices
that include medical gas cylinders in machine hanger yokes, pressure
regulating and measuring devices, valves, flow controllers, flow meters,
vaporizers, CO2 absorber canisters, and
breathing circuit assembly. The basic
The anesthesia machine is a basic tool of the anesthesiologist/anesthetist and serves as the primary work station. It allows the anesthesia provider to select and mix measured flows of gases, to vaporize controlled amounts of liquid anesthetic agents, and thereby to administer safely controlled concentrations of oxygen and anesthetic gases and vapors to the patient via a breathing circuit. The anesthesia machine also provides a working surface for placement of drugs and devices for immediate access and drawers for storage of small equipment, drugs, supplies, and equipment instruction manuals. Finally, the machine serves as a frame and source of pneumatic and electric power for various accessories such as a ventilator, and monitors that observe or record vital patient functions or that are critical to the safe administration of anesthesia.
Gas Flow in the Anesthesia Machine and Breathing System
The internal piping of a basic
Because pipeline systems can fail and because the machines may be
used in locations where piped gases are not available, anesthesia
machines are fitted with reserve cylinders of oxygen and
N2O. The oxygen cylinder source is regulated
from approximately 2,200 psig in the tanks to approximately 45 psig in
Figure 1. The flow arrangement of a basic
two-gasanesthesia machine. A, The fail-safevalve in Ohmeda machines is termed a pressure sensor shut-offvalve; in Dräger machines it is the oxygen failure protection device (OFPD). B, Second-stageoxygen pressure regulator is used in Ohmeda (but not Dräger Narkomed) machines. C, Second-stagenitrous oxide pressure regulator is used in Ohmeda Modulus machines having the Link 25 Proportion Limiting System; not used in Dräger machines. D, Pressure relief valve used in certain Ohmeda machines; not used in Dräger machines. E, Outlet check valve used in Ohmeda machines except Modulus II Plus and Modulus CD models; not used in Dräger machines. The oxygen take-offfor the anesthesia ventilator driving gas circuit is downstream of the main on/off switch in Dräger machines, as shown here. In Ohmeda machines, the take-offis upstream of the main on/off switch. (Adapted from Check-out:a guide for preoperative inspection of an anesthesia machine, ASA, 1987. Reproduced by permission of the American Society of Anesthesiologists, 520 N. Northwest Highway, Park Ridge, Ill.)
Figure 2. The supply of nitrous oxide and oxygen may come from two sources: the wall (pipeline) supply and the reserve cylinder supply. (Reproduced by permission of Datex·Ohmeda, Madison, Wisconsin).
Compressed gas cylinders of oxygen, N2O, and other medical gases are attached to the anesthesia machine through the hanger yoke assembly. Each hanger yoke is equipped with the pin index safety system, a safeguard introduced to eliminate cylinder interchanging and the possibility of accidentally placing the incorrect gas tank in a yoke designed for another gas tank.
Figure 3 shows the oxygen pathway through the flowmeter, the agent
vaporizer, and the machine piping, and into the breathing circuit.
Oxygen from the wall outlet or cylinder pressurizes the anesthesia
delivery system. Compressed oxygen provides the needed energy for a
pneumatically powered ventilator, if used, and it supplies the oxygen
flush valve used to supplement oxygen flow to the breathing circuit.
Oxygen also"powers" an
Figure 3. Oxygen and N2O flow from their supply sources via their flow control valves, flowmeters and common manifold to the
concentration-calibratedvaporizer and then via the machine common gas outlet to the breathing system. The high pressure system of the anesthesia machine comprises those components from the compressed gas supply source to the gas (O2 and N2O) flow control valves. The low pressure system of the anesthesia machine comprises those components downstream of the gas flow control valves. (Reproduced by permission of Datex·Ohmeda, Madison, Wisconsin).
Once the flows of oxygen, N2O, and other
medical gases (if used) are turned on at their flow control valves, the
gas mixture flows into the common manifold and through a
The circle system shown in Figure 4 is the breathing system most commonly used in operating rooms (ORs). It is so named because its components are arranged in a circular manner. The essential components of a circle breathing system (Figure 5) include a site for inflow of fresh gas (common [fresh] gas inlet), a carbon dioxide absorber canister (containing soda lime or barium hydroxide lime) where exhaled carbon dioxide is absorbed; a reservoir bag; inspiratory and
Figure 4. Basic circle breathing system. (Reproduced by permission of Datex·Ohmeda, Madison, Wisconsin).
expiratory unidirectional valves; flexible corrugated breathing
tubing; an adjustable
Figure 5. Essential components of a circle breathing system. (Adapted from Principles of Anesthesiology: general and regional anesthesia, Collins, Vincent J., M.D., Executive Editor: Cann, Carroll C., 1993. Reproduced by permission of Lippincott Williams and Wilkins, Malvern, Pennsylvania).
Once inside the breathing system, the mixture of gases and vapors
flows to the breathing system’s inspiratory unidirectional valve, then
on toward the patient. Exhaled gases pass through the expiratory
unidirectional valve and enter the reservoir bag. When the bag is full,
excess gas flows through the APL (or
When an anesthesia ventilator is used, the ventilator bellows
functionally replaces the circle system reservoir bag and becomes a part
of the breathing circuit. The APL valve in the breathing circuit is
either closed or excluded from the circuit using a manual
("bag")/automatic (ventilator) circuit selector switch. The ventilator
Sources of Leaks Within the Anesthesia Machine and Breathing System
No anesthesia machine system is totally
The high-pressure system consists of all piping and parts of the
machine that receive gas at cylinder or pipeline supply pressure. It
extends from the
The low-pressure system of the anesthesia machine (in which the
pressure is slightly above atmospheric) consists of components
downstream of the
Low-pressure system leaks also may occur at the gas analysis sensor
(i.e., circuit oxygen analyzer) and gas sampling site(s), face mask, the
tracheal tube (especially in pediatric patients where a leak is required
around the uncuffed tracheal tube), laryngeal mask airway (over the
larynx), and connection points for accessory devices such as a
humidifier, temperature probe, or positive
Minute absorbent particles that may have been spilled on the rubber
seal around the absorber canister(s) may also prevent a
Checking Anesthesia Machines
Prior to induction of anesthesia, the anesthesia machine and its
components/accessories should be made ready for use. All parts of the
machine should be in good working order with all accessory equipment and
necessary supplies on hand. The waste gas disposal system should be
connected, hoses visually inspected for obstructions or kinks, and
proper operation determined. Similarly, the anesthesia breathing system
should be tested to verify that it can maintain positive pressure. Leaks
should be identified and corrected before the system is used (Bowie
and Huffman 1985; Food
and Drug Administration 1993; Dorsch
and Dorsch 1994). The ability of the anesthesia system to maintain
constant pressure is tested not only for the safety of the patient
dependent on a generated positive pressure ventilation but also to test
for leaks and escape of anesthetic gases, which may expose
Occupational exposures can be controlled by the application of a number
The following is a general discussion of engineering controls, work
practices, administrative controls, and personal protective equipment that
can reduce worker exposure to waste anesthetic gases. However, not every
control listed in this section may be feasible in all settings. Additional
The collection and disposal of waste anesthetic gases in operating
The exhalation of residual gases by patients in the PACU may result in significant levels of waste anesthetic gases when appropriate work practices are not used at the conclusion of the anesthetic or inadequate ventilation exists in the PACU. A nonrecirculating ventilation system can reduce waste gas levels in this area. Waste gas emissions to the outside atmosphere must meet local, state, and Environmental Protection Agency (EPA) regulatory requirements.
A scavenging system consists of five basic components (ASTM, F 1343 - 91):
A gas collection assembly such as a collection manifold or a
distensible bag (i.e.,
Transfer tubing, which conveys the excess anesthetic gases to the interface.
The interface, which provides positive (and sometimes negative) pressure relief and may provide reservoir capacity. It is designed to protect the patient's lungs from excessive positive or negative scavenging system pressure.
Gas disposal assembly tubing, which conducts the excess anesthetic gases from the interface to the gas disposal assembly.
The gas disposal assembly, which conveys the excess gases to
a point where they can be discharged safely into the atmosphere.
Several methods in use include a nonrecirculating or recirculating
ventilation system, a central vacuum system, a dedicated
In general, a
Removal of excess anesthetic gases from the anesthesia circuit can be accomplished by either active or passive scavenging. When a vacuum or source of negative pressure is connected to the scavenging interface, the system is described as an active system. When a vacuum or negative pressure is not used, the system is described as a passive system. With an active system there will be a negative pressure in the gas disposal tubing. With a passive system, this pressure will be increased above atmospheric (positive) by the patient exhaling passively, or manual compression of the breathing system reservoir bag.
Use of a central vacuum system is an example of an active system: The waste anesthetic gases are moved along by negative pressure. Venting waste anesthetic gas via the exhaust grille or exhaust duct of a nonrecirculating ventilation system is an example of a passive system: The anesthetic gas is initially moved along by the positive pressure from the breathing circuit until it reaches the gas disposal assembly.
Excess anesthetic gases may be removed by a central vacuum system (servicing the ORs in general) or an exhaust system dedicated to the disposal of excess gases. When the waste anesthetic gas scavenging system is connected to the central vacuum system (which is shared by other users, e.g., surgical suction), exposure levels may be effectively controlled. The central vacuum system must be specifically designed to handle the large volumes of continuous suction from OR scavenging units. If a central vacuum system is used, a separate, dedicated gas disposal assembly tubing should be used for the scavenging system, distinct from the tubing used for patient suctioning (used for oral and nasal gastric sources as well as surgical suctioning).
Similarly, when a dedicated exhaust system (low velocity) is used,
excess gases can also be collected from one or more ORs and discharged
to the outdoors. The exhaust fan must provide sufficient negative
pressure and air flow so that
HVAC systems used in
When a nonrecirculating ventilation system serves through
Concern for fuel economy has increased the use of systems that recirculate air. Recirculating HVAC/ventilation systems return part of the exhaust air back into the air intake and recirculate the mixture through the room. Thus, only a fraction of the exhaust air is disposed of to the outside. To maintain minimal levels of anesthetic exposure, air which is to be recirculated must not contain anesthetic gases. Consequently, recirculating systems employed as a disposal pathway for waste anesthetic gases must not be used for gas waste disposal. The exception is an arrangement that transfers waste gases into the ventilation system at a safe distance downstream from the point of recirculation to ensure that the anesthetic gases will not be circulated elsewhere within the building.
Under certain circumstances a separate duct for venting anesthetic
gases directly outside the building without the use of a fan, may be an
acceptable alternative. By this technique, excess anesthetic gases may
be vented through the wall, window, ceiling, or floor, relying only on
the slight positive pressure of the gases leaving the gas collection
assembly to provide the flow. However, several limitations are apparent.
A separate line would be required for each OR to prevent the
Adsorbers can also trap most excess anesthetic gases. Canisters of varying shapes and capacities filled with activated charcoal have been used as waste gas disposal assemblies by directing the gases from the gas disposal tubing through them. Activated charcoal canisters will effectively adsorb the vapors of halogenated anesthetics but not N2O. The effectiveness of individual canisters and various brands of charcoal vary widely. Different potent inhaled volatile agents are adsorbed with varying efficiencies. The efficiency of adsorption also depends on the rate of gas flow through the canister. The canister is used where portability is necessary. The disadvantages are that they are expensive and must be changed frequently. Canisters must be used and discarded in the appropriate manner, as recommended by the manufacturer.
General or Dilution Ventilation
An effective room HVAC system when used in combination with an
anesthetic gas scavenging system should reduce, although not entirely
eliminate, the contaminating anesthetic gases. If excessive
concentrations of anesthetic gases are present, then airflow should be
increased in the room to allow for more air mixing and further dilution
of the anesthetic gases. Supply register louvers located in the ceiling
should be designed to direct the fresh air toward the floor and toward
Work practices, as distinct from engineering controls, involve the way in which a task is performed. OSHA has found that appropriate work practices can be a vital aid in reducing the exposures of OR personnel to waste anesthetic agents. In contrast, improper anesthetizing techniques can contribute to increased waste gas levels. These techniques can include an improperly selected and fitted face mask, an insufficiently inflated tracheal tube cuff, an improperly positioned laryngeal mask, or other airway, and careless filling of vaporizers and spillage of liquid anesthetic agents.
General work practices recommended for anesthetizing locations include the following:
A complete anesthesia apparatus checkout procedure should be performed each day before the first case. An abbreviated version should be performed before each subsequent case. The FDA Anesthesia Apparatus Checkout Recommendations (Appendix 2) should be considered in developing inspection and testing procedures for equipment checkout prior to administering an anesthetic.
If a face mask is to be used for administration of inhaled anesthetics, it should be available in a variety of sizes to fit each patient properly. The mask should be pliable and provide as effective a seal as possible against leakage into the surrounding air.
Tracheal tubes, laryngeal masks, and other airway devices should be positioned precisely and the cuffs inflated adequately.
Vaporizers should be filled in a
Spills of liquid anesthetic agents should be cleaned up promptly.
(Refer to section
Before extubating the patient's trachea or removing the mask or
other airway management device, one should administer
Work practices performed by biomedical engineers and technicians also contribute significantly to the efficacy of managing waste gas exposure. It is, therefore, important for this group of workers to do the following:
Monitor airborne concentrations of waste gases by sampling,
measuring, and reporting data to the institution's administration. Air
monitoring for waste anesthetic gases should include both personal
sampling (i.e., in a
Assist in identifying sources of waste/leaking gases and implementing corrective action.
Determine if the scavenging system is designed and functioning
properly to remove the waste anesthetic gases from the breathing
circuit, and ensure that the gases are vented from the workplace in
such a manner that occupational
Ensure that operatory and PACU ventilation systems provide sufficient room air exchange to reduce ambient waste gas levels.
Administrative controls represent another approach for reducing
worker exposure to waste gases other than through the use of engineering
controls, work practices, or personal protective equipment.
Administrative controls may be thought of as any administrative decision
that results in decreased
Institute a program of routine inspection and regular maintenance of equipment in order to reduce anesthetic gas leaks and to have the best performance of scavenging equipment and room ventilation. Preventive maintenance should be performed by trained individuals according to the manufacturer’s recommendations and at intervals determined by equipment history and frequency of use. Preventive maintenance includes inspection, testing, cleaning, lubrication, and adjustment of various components. Worn or damaged parts should be repaired or replaced. Such maintenance can result in detection of deterioration before an overt malfunction occurs. Documentation of the maintenance program should be kept indicating the nature and date of the work performed, as well as the name of the trained individual servicing the equipment.
Implement a monitoring program to measure airborne levels of waste
gases in the breathing zone or immediate work area of those most
heavily exposed (e.g., anesthesiologist, nurse anesthetist, oral
surgeon) in each anesthetizing location and PACU. Periodic monitoring
(preferably at least semiannually) of waste gas concentrations is
needed to ensure that the anesthesia delivery equipment and
engineering/environmental controls work properly and that the
maintenance program is effective. Monitoring may be performed
effectively using conventional
Encourage or promote the use of scavenging systems in all anesthetizing locations where inhaled agents are used, recognizing that a waste gas scavenging system is the most effective means of controlling waste anesthetic gases.
Implement an information and training program for employees exposed to anesthetic agents that complies with OSHA’s Hazard Communication Standard (29 CFR 1910.1200) so that employees can meaningfully participate in, and support, the protective measures instituted in their workplace.
Define and implement appropriate work practices to help reduce employee exposure. Training and educational programs covering appropriate work practices to minimize levels of anesthetic gases in the operating room should be conducted at least annually. Employers should emphasize the importance of implementing these practices and should ensure that employees are properly using the appropriate techniques on a regular basis.
Implement a medical surveillance program for all workers exposed to waste gases.
Ensure the proper use of personal protective equipment during
Manage disposal of liquid agents, spill containment, and air monitoring for waste gases following a spill.
Comply with existing federal, state, and local regulations and guidelines developed to minimize personnel exposure to waste anesthetic gases, including the proper disposal of hazardous chemicals.
Personal Protective Equipment
Personal protective equipment should not be used as a substitute for
engineering, work practice, and/or administrative controls in
anesthetizing locations and PACUs. In fact, exposure to waste gases is
not effectively reduced by gloves, goggles, and surgical masks. A
When selecting gloves and CPC, some of the factors to be considered include material chemical resistance, physical strength and durability, and overall product integrity. Permeation, penetration, and degradation data should be consulted if available. Among the most effective types of gloves and body protection are those made from Viton®, neoprene, and nitrile. Polyvinyl alcohol (PVA) is also effective but it should not be exposed to water or aqueous solutions.
When the gloves and the CPC being used have not been tested under the expected conditions, they may fail to provide adequate protection. In this situation, the wearer should observe the gloves and the chemical protective clothing during use and treat any noticeable change (e.g., color, stiffness, chemical odor inside) as a failure until proved otherwise by testing. If the work must continue, new CPC should be worn for a shorter exposure time, or CPC of a different generic material should be worn. The same thickness of a generic material such as neoprene or nitrile supplied by different manufacturers may provide significantly different levels of protection because of variations in the manufacturing processes or in the raw materials and additives used in processing.
Professional judgement must be used in determining the type of
respiratory protection to be worn. For example, where spills of
halogenated anesthetic agents are small, exposure time brief, and
sufficient ventilation present,
Where large spills occur and there is insufficient ventilation to adequately reduce airborne levels of the halogenated agent, respirators designed for increased respiratory protection should be used. The following respirators, to be selected for large spills, are ranked in order from minimum to maximum respiratory protection:
Any type 'C'
Any type 'C'
This section describes engineering and work practice controls specific to hospital ORs, PACUs, dental operatories, and veterinary clinics and hospitals. Operational procedures relating to engineering controls are also discussed where appropriate.
Hospital Operating Rooms
For years anesthesia providers tolerated exposure to waste anesthetic
gases and regarded it as an inevitable consequence of their work. Since
the 1970s anesthesiologists have steadily worked to improve equipment
and technique to reduce workplace exposures to waste anesthetic gases,
and significant progress has been made. In early delivery equipment,
waste gases were exhausted through the APL or
Waste gas evacuation is required for every type of breathing
circuit configuration (Huffman
and Eisenkraft 1993), with the possible exception of a closed
circuit, because most anesthesia techniques typically use more fresh
gas flow than is required. Appropriate waste gas evacuation involves
collection and removal of waste gases, detection and correction of
leaks, consideration of work practices, and effective room ventilation
and Dorsch 1994). To minimize waste anesthetic gas concentrations
in the operating room the recommended air exchange rate (room dilution
ventilation) is a minimum total of 15 air changes per hour with a
minimum of 3 air changes of outdoor air (fresh air) per hour (American
Institute of Architects
In most patients, a circle absorption system is used and can be
easily connected to a waste gas scavenging system. In pediatric
anesthesia, systems other than those with a circle absorber may be
used. Choice of the breathing circuit that best meets the needs of
pediatric patients may alter a clinician’s ability to scavenge waste
gas effectively. Breathing circuits frequently chosen for neonates,
infants, and small children are usually valveless, have low
resistance, and limit rebreathing. The Mapleson D system and the
The following work practices may be employed with any of the above breathing circuits:
Empty the contents of the reservoir bag directly into the anesthetic gas scavenging system and turn off the flow of N2O and any halogenated anesthetic agent prior to disconnecting the patient circuit.
Turn off the flow of N2O and the vaporizer, if appropriate, when the patient circuit is disconnected from the patient, for example, for oral or tracheal suctioning.
Test daily for
If the circle absorber system (Figure 6) is used, the following additional work practices can be employed:
Adjust the vacuum needle valve as needed to regulate the flow of
waste anesthetic gases into the vacuum source in an active
scavenging system. Adjustments prevent the bag from overdistending
by maintaining the volume in the scavenging system reservoir bag
between empty and
Cap any unused port in a passive waste gas scavenging configuration.
Figure 6. Circle breathing system connected to a closed reservoir scavenging interface. (Reproduced by permission of North American Dräger, Telford, Pennsylvania).
Postanesthesia Care in Hospitals and
Because the patient is the main source of waste anesthetic gases in
the PACU, it becomes more difficult to control
As a result of using appropriate anesthetic gas scavenging in ORs,
the levels of contamination have been decreased. In the PACU, however,
the principle of scavenging as practiced in the OR is not widely
accepted due to medical considerations and consequently is
infrequently employed as a
PACU managers should consider:
Periodic exposure monitoring with particular emphasis on peak gas levels in the breathing zone of nursing personnel working in the immediate vicinity of the patient’s head. Methods using random room sampling to assess ambient concentrations of waste anesthetic gases in the PACU are not an accurate indicator of the level of exposure experienced by nurses providing bedside care. Because of the closeness of the PACU nurse to the patient, such methods would consistently underestimate the level of waste anesthetic gases in the breathing zone of the bedside nurse.
Application of a routine ventilation system maintenance program to keep waste gas exposure levels to a minimum.
Mixtures of N2O and oxygen have been used in dentistry as general anesthetic agents, analgesics, and sedatives for more than 100 years (McGlothlin et al. 1992). The usual analgesia equipment used by dentists includes a N2O and O2 delivery system, a gas mixing bag, and a nasal mask with a positive pressure relief valve (Dorsch and Dorsch 1994). The analgesia machine is usually adjusted to deliver more of the analgesic gas mixture than the patient can use.
Analgesia machines for dentistry are designed to deliver up to 70 percent (700,000 ppm) N2O to a patient during dental surgery. The machine restricts higher concentrations of N2O from being administered to protect the patient from hypoxia. In most cases, patients receive between 30 and 50 percent N2O during surgery. The amount of time N2O is administered to a patient depends on the dentist’s judgment of patient needs and the complexity of the surgery. The most common route of N2O delivery and exhaust is through a nasal scavenging mask applied to the patient.
Some dentists administer N2O at higher concentrations at the beginning of the operation, then decrease the amount as the operation progresses. Others administer the same amount of N2O throughout the operation. When the operation is completed, the N2O is turned off. Some dentists turn the N2O on only at the beginning of the operation, using N2O as a sedative during the administration of local anesthesia, and turn it off before operating procedures. Based on variations in dental practices and other factors in room air, N2O concentrations can vary considerably for each operation and also vary over the course of the operation.
Unless the procedure is performed under general anesthesia in an OR, halogenated anesthetics are not administered, nor does the patient undergo laryngoscopy and tracheal intubation. In the typical dental office procedure, the nasal mask is placed on the patient, fitted, and adjusted prior to administration of the anesthetic agent. The mask is designed for the nose of the patient since access to the patient’s mouth is essential for dental procedures.
A local anesthetic, if needed, is typically administered after the
N2O takes effect. The patient’s mouth is
opened and the local anesthetic is injected. The dental procedure begins
after the local anesthetic takes effect. The patient opens his/her mouth
but is instructed to breathe through the nose. Nonetheless, a certain
amount of mouth breathing frequently occurs. The dentist may
periodically stop the dental procedure for a moment to allow the patient
to close the mouth and breath deeply to
At the end of the procedure, the nosepiece is left on the patient while the N2O is turned off and the oxygen flow is increased. The anesthetic mixture diffuses from the circulating blood into the lungs and is exhaled. Scavenging is continued while the patient is eliminating the N2O.
The dental office or operatory should have a properly installed N2O delivery system. This includes appropriate scavenging equipment with a readily visible and accurate flow meter (or equivalent measuring device), a vacuum pump with the capacity for up to 45 L/min of air per workstation, and a variety of sizes of masks to ensure proper fit for individual patients.
A common nasal mask, shown in Figure 7, consists of an inner and a slightly larger outer mask component. The inner mask has two hoses connected that supply anesthetic gas to the patient. A relief valve is attached to the inner mask to release excess N2O into the outer mask. The outer mask has two smaller hoses connected to a vacuum system to capture waste gases from the patient and excess gas supplied to the patient by the analgesia machine. The nasal mask should fit over the patient’s nose as snugly as possible without impairing the vision or dexterity of the dentist. Gases exhaled orally are not captured by the nasal mask. A flow rate of approximately 45 L/min has been recommended as the optimum rate to prevent significant N2O leakage into the room air (NIOSH 1994).
Figure 7. A nasal mask designed to allow waste gases to be scavenged through the nose piece.
A newer type of mask is a frequent choice in dental practice: a single patient use nasal hood. This mask does not require sterilization after surgery because it is used by only one patient and is disposable.
In a dental operatory, a scavenging system is part of a
The general ventilation should provide good room air mixing. In
addition, auxiliary (local) exhaust ventilation used in conjunction
with a scavenging system has been shown to be effective in reducing
excess N2O in the breathing zone of the
dentist and dental assistant, from nasal mask leakage and patient
mouth breathing (NIOSH
1994). This type of ventilation captures the waste anesthetic
gases at their source. However, there are practical limitations in
using it in the dental operatory. These include proximity to the
patient, interference with dental practices, noise, and installation
and maintenance costs. It is most important that the dentist not work
between the patient and a
Prior to first use each day of the N2O
machine and every time a gas cylinder is changed, the
Prior to first use each day, inspect all N2O equipment (e.g., reservoir bag, tubing, mask, connectors) for worn parts, cracks, holes, or tears. Replace as necessary.
Connect mask to the tubing and turn on vacuum pump. Verify appropriate flow rate (i.e., up to 45 L/min or manufacturer’s recommendations).
A properly sized mask should be selected and placed on the
patient. A good, comfortable fit should be ensured. The reservoir
(breathing) bag should not be
Encourage the patient to minimize talking, mouth breathing, and facial movement while the mask is in place.
During N2O administration, the reservoir bag should be periodically inspected for changes in tidal volume, and the vacuum flow rate should be verified.
On completing anesthetic administration and before removing the
Veterinary Clinics and Hospitals
Inhalation anesthesia in veterinary hospitals is practiced in a
manner similar to that in human hospitals. Generally, animals are
initially given an injectable anesthetic, followed by general anesthesia
maintained by an inhalation technique. In animal anesthesia, there are
five basic methods by which inhalation anesthetics are administered:
|A. Oxygen source||F. Y-Piece connecting inspiratory|
|B. Pressure reducing valve||And expiratory hoses|
|C. Flow meter||G. Expiratory valve|
|D. Vaporizer||H. Reservoir bag|
|E. Inspiratory valve||I. Carbon dioxide absorber|
|J. Pop-off valve|
Figure 8. Circle breathing system used for veterinary anesthesia. (Reproduced by permission of American Industrial Hygiene Association, Fairfax, Virginia).
Unidirectional valves allow flow from the vaporizer to the animal
upon inspiration and route the exhaled gases through a carbon dioxide
absorber during expiration. High
Controlled rebreathing systems used for very small animals allow
exhaled gases to be immediately expelled from the system into the room
air. Because these systems do not include a carbon dioxide absorber,
The basic principles of scavenging used to capture excess
anesthetic gases in hospital surgical suites are appropriate for
application in veterinary anesthesia. The APL or
In general, the disposal pathway for waste anesthetic gases
generated in a veterinary facility can be any one of those mentioned
(e.g., ventilation system, central vacuum system, dedicated blower
[exhaust] system, passive duct system, or adsorber) and described in
detail on pages [
The following are recommended work practices for reducing gas leakage:
Avoid turning on N2O or a vaporizer until the circuit is connected to the animal. Switch off the N2O and vaporizer when not in use. Maintain oxygen flow until the scavenging system is flushed.
Select the optimal size tracheal tube for the animal and make
sure the cuff, if present, is adequately inflated. Adequacy of cuff
inflation may be evaluated by delivering a
Once anesthesia is discontinued, empty the breathing bag into the scavenging system rather than into the room. Releasing anesthetic gases into the OR could significantly increase the overall waste gas concentration within the room.
At the end of the surgical procedure, continue to
It is possible to close an anesthetic circle and reduce
Select masks to suit various sizes and breeds encountered in veterinary practice. When a mask is used for induction or maintenance of anesthesia, use a mask that properly fits the contour of the animal’s face to minimize gas leakage. Minimize the time of mask anesthesia to reduce waste.
Use a box for induction of anesthesia in small, uncooperative
animals. As with the mask technique, the induction box method
Make certain that the reservoir bag, used to store excess
anesthetic waste gas until the vacuum system can remove it, is
adequate to contain all scavenged gas. This reservoir bag is
especially designed to connect to anesthetic
Small volumes of liquid anesthetic agents such as halothane, enflurane, isoflurane, desflurane, and sevoflurane evaporate readily at normal room temperatures, and may dissipate before any attempts to clean up or collect the liquid are initiated. However, when large spills occur, such as when one or more bottles of a liquid agent break, specific cleaning and containment procedures are necessary and appropriate disposal is required (AANA 1992). The recommendations of the chemical manufacturer’s material safety data sheet (MSDS) that identify exposure reduction techniques for spills and emergencies should be followed.
In addition, OSHA Standard for Hazardous Waste Operations and Emergency
Response (29 CFR 1910.120)
would apply if emergency response efforts are performed by employees. The
employer must determine the potential for an emergency in a reasonably
Because of the volatility of liquid anesthetics, rapid removal by
suctioning in the OR is the preferred method for cleaning up spills.
Spills of large volumes in poorly ventilated areas or in storage areas
should be absorbed using an absorbent material, sometimes called a
sorbent, that is designed for
Both enflurane and desflurane are considered hazardous wastes under the
EPA regulations because these chemicals contain trace amounts of
chloroform (a hazardous substance), a
To minimize exposure to all liquid anesthetic agents during
Determination of appropriate disposal procedures for each facility is the sole responsibility of that facility. Empty anesthetic bottles are not considered regulated waste and may be discarded with ordinary trash or recycled. Furthermore, the facility as well as the waste handling contractor must comply with all applicable federal, state, and local regulations.
To minimize exposure to waste liquid anesthetic agents during
Where possible, ventilate area of spill or leak. Appropriate respirators should be worn.
Restrict persons not wearing protective equipment from areas of
spills or leaks until
Collect the liquid spilled and the absorbent materials used to contain a spill in a glass or plastic container. Tightly cap and seal the container and remove it from the anesthetizing location. Label the container clearly to indicate its contents.
Transfer the sealed containers to the waste disposal company that handles and hauls waste materials.
Health-care facilities that own or operate medical waste incinerators may dispose of waste anesthetics by using an appropriate incineration method after verifying that individual incineration operating permits allow burning of anesthetic agents at each site.
Air monitoring is one of the fundamental tools used to evaluate
workplace exposures. Accordingly, this section presents some of the
appropriate methods that can be used to detect and measure the
concentration of anesthetic gases that may be present in the
OSHA recommends that air sampling for anesthetic gases be conducted
every 6 months to measure worker exposures and to check the effectiveness
of control measures. Furthermore, OSHA recommends that only the agent(s)
most frequently used needs to be monitored, since proper engineering
controls, work practices and control procedures should reduce all agents
proportionately. However, the decision to monitor only selected agents
could depend not only on the frequency of their use, but on the
availability of an appropriate analytical method and the cost of
instrumentation. [ASA emphasizes regular maintenance of equipment and
scavenging systems, daily
Three fundamental types of air samples can be taken in order to
evaluate the workplace: personal, area, and source samples. Personal
samples give the best estimate of a worker’s exposure level since they
represent the actual airborne contaminant concentration in the worker’s
breathing zone during the sampling period. This is the preferred method
for determining a worker’s
Area sampling is useful for evaluating overall air contaminant levels
in a work area and for investigating
The OSHA Chemical Information Manual contains current sampling technology for several of the anesthetic gases that may be present in anesthetizing locations and PACUs. Some of the sampling methods available are summarized below.
Personal N2O exposures can be determined by using the VAPOR-TRAK nitrous oxide passive monitor (sometimes called a"passive dosimeter" or"diffusive sampler") as referenced in the 2000 OSHA Chemical Information Manual under IMIS:1953. The minimum sampling duration for the dosimeter is 15 minutes; however, it can be used for up to 16 hours of passive sampling. This sampler has not been validated by OSHA. Other dosimeters are commercially available and can be used. Although not validated by OSHA at this time, they may be validated in the future. Five liter, 5-layer aluminized gas sampling bags can also be used to collect a sample.
The current recommended media sampling for halothane, enflurane, and isoflurane requires an Anasorb 747 tube (140/70 mg sections) or an Anasorb CMS tube (150/75 mg. sections). The sample can be taken at a flow rate of 0.5 L/min. Total sample volumes not exceeding 12 liters are recommended. The current recommended sampling media for desflurane requires an Anasorb 747 tube (140/70 mg sections). The sample can be taken at a flow rate of 0.05 L/min. Total sample volumes not exceeding 3 liters are recommended. All four sampling methodologies are fully validated analytical procedures.
Sampling that provides direct, immediate, and continuous (real-time) readout of anesthetic gas concentrations in ambient air utilizes a portable infrared spectrophotometer. Since this method provides continuous sampling and instantaneous feedback, sources of anesthetic gas leakage and effectiveness of control measures can be immediately determined.
Additional Sampling Guidelines
If it should ever be necessary to enter an operating room to conduct air sampling, the following guidelines provide the information needed. Individuals performing air sampling should be familiar with and follow all OR procedures for access into and out of the surgical suite with particular attention to sterile and nonsterile areas. The patient is the center of the sterile field, which includes the areas of the patient, operating table, and furniture covered with sterile drapes and the personnel wearing sterile attire. Sampling in the breathing zone of surgeons and other nursing or technical personnel who work in the sterile field must conform to the principles of sterile field access. Strict adherence to sound principles of sterile technique and recommended practices is mandatory for the safety of the patient.
Generally speaking, each hospital has its own guidelines for proper
OR attire and other safety procedures. These rules should be strictly
followed by anyone entering the OR. There are standard uniform
guidelines that apply to all hospitals. Only clean and/or freshly
laundered OR attire is worn in the OR. Proper attire consists of body
covers such as a
In regard to decontaminating outside equipment, each hospital has its own policy. However, the common practice is to "wipe off" all surfaces with a chemical disinfectant. Most hospitals use Wescodyne or other phenolic solutions. Good physical cleaning before disinfection helps reduce the number of microorganisms present and enhances biocidal action.
Any person not familiar with the OR is usually instructed by a scrub nurse on all the safety procedures pertaining to the hospital. The scrub nurse will also provide instructions on hand scrubbing and other procedures that may be necessary. Persons entering the OR must follow these guidelines and instructions.
In addition, it should be recognized that the patient’s welfare, safety, and rights of privacy are paramount.
In all locations where anesthesia is administered, engineering controls
such as a scavenging system to remove waste anesthetic gases and adequate
room ventilation should be utilized. Medical surveillance of personnel
working in scavenged operating rooms is intended primarily to establish a
baseline. Routine annual
A preplacement medical questionnaire that includes a detailed work
history (including past exposures to waste anesthetic gases); a medical
history with emphasis on: hepatic (liver), renal (kidney), neurological
(nervous system), cardiovascular (heart and circulation), and
reproductive functions. Pertinent positive response(s) to the
questionnaire should be followed by an appropriate medical evaluation
An annual questionnaire emphasizing the issues mentioned above. Again, the need for physical examination or laboratory work may be based on questionnaire responses.
A system should be created for employees to report health problems which they believe may be associated with anesthetic exposure. Employees should be informed of this reporting system and of the method by which reports can be submitted.
An acute exposure ( i.e., a sudden,
A reproductive hazards policy should also be in place at the facility and should address worker exposure and reproductive health effects in male and female employees. The facility should provide training in the known and potential adverse health effects, including reproductive effects, of waste anesthetic gases, as is required for chemicals covered by the Hazard Communication Standard.
A final medical review upon job transfer or termination. This should be in the form of a questionnaire that includes any acute or significant exposures as well as a review of symptoms and signs detected during employment, along with a medical evaluation when appropriate.
Medical and exposure records developed for employees who may be exposed to hazardous chemicals such as N2O and halogenated anesthetic agents must be retained, made available, and transferred in accordance with OSHA Standard for Access to Employee Exposure and Medical Records (29 CFR 1910.1020). The occurrence of injury or illness related to occupational exposure must be recorded in accordance with OSHA recordkeeping regulations (29 CFR 1904).
In accordance with the Hazard Communication Standard (29 CFR 1910.1200),
Any chemicals subject to the labeling requirements of the FDA are exempt from the labeling requirements under the Hazard Communication Standard. This includes such chemicals as volatile liquid anesthetics and compressed medical gases. However, containers of other chemicals not under the jurisdiction of the FDA must be labeled, tagged, or marked with the identity of the material and must show appropriate hazard warnings as well as the name and address of the chemical manufacturer, importer, or other responsible party. The hazard warning can be any type of message --words, pictures, or symbols-- that conveys the hazards of the chemical(s) in the container. Labels must be legible, in English (plus other languages if desired), and prominently displayed.
Each MSDS must be in English, although the employer may maintain copies
in other languages as well, and must include information regarding the
specific chemical identity of the anesthetic gases or hazardous chemical
and its common names. In addition, information must be provided on the
physical and chemical characteristics of the hazardous chemical, known
acute and chronic health effects and related health information, primary
route(s) of entry, exposure limits, precautionary measures, emergency and
Employers must prepare a list of all hazardous chemicals in the workplace, and the list should be checked to verify that MSDSs have been received for each chemical. If there are hazardous chemicals used for which no MSDS has been received, the employer must contact the supplier, manufacturer, or importer to obtain the missing MSDS.
Health-care employers must establish a training and information program for all personnel who are involved in the handling of, or who have potential exposure to, anesthetic gases and other hazardous chemicals to apprise them of the hazards associated with these chemicals in the workplace. Training relative to anesthetic gases should place an emphasis on reproductive risks. Training and information must take place at the time of initial assignment and whenever a new hazard is introduced into the work area. At a minimum, employees must be informed of the following:
The Hazard Communication Standard (29 CFR 1910.1200) and its requirements.
Any operations and equipment in the work area where anesthetic agents and hazardous chemicals are present.
Location and availability of the written hazard communication program including the required lists of hazardous chemicals and the required MSDS forms.
The employee training program must consist of the following elements:
How the hazard communication program is implemented in the workplace, how to read and interpret information on the MSDS and label of each hazardous chemical, and how employees can obtain and use the available hazard information.
The physical and health hazards of the chemicals in the work area.
Measures employees can take to protect themselves from these hazards, including specific procedures put into effect by the employer to provide protection such as engineering controls, appropriate work practices, emergency procedures for spill containment, and the use of personal protective equipment.
Methods and observations that may be used to detect the presence or release of anesthetic gases and other hazardous chemicals in the work area (such as monitoring conducted by the employer, continuous monitoring devices, and the appearance or odor of chemicals when released).
Personnel training records are not required to be maintained, but such
records would assist employers in monitoring their programs to ensure that
all employees are appropriately trained. Employers can provide employees
information and training through whatever means are found appropriate and
protective. Although there would always have to be some training
American Association of Nurse Anesthetists (AANA). 1992.
Management of Waste Anesthetic Gases. Park Ridge, IL: Author. Pp.
American Conference of Governmental Industrial Hygienists
(ACGIH). 1989. Threshold Limit Values and Biological Exposure Indices
American Institute of Architects. Academy of Architecture
for Health. Guidelines for Design and Construction of Hospital and
Health Care Facilities,
American Society of Anesthesiologists. 1974. Occupational
Disease Among Operating Room Personnel: A National Study. Report of an Ad
Hoc Committee on the Effect of Trace Anesthetics on the Health of
Operating Room Personnel. Anesthesiology 41:
American Society for Testing and Materials. 1988.
Standard Specification for Minimum Performance and Safety Requirements
for Components and Systems of Anesthesia Gas Machines. West
Conshohocken, PA: Author.
__________. 1991. Standard Specification for Anesthetic
Equipment--Scavenging Systems for Anesthetic Gases.West Conshohocken,
Askrog, V., and Petersen, R. 1970. Forurening af Operationsstuer Med Lurtformige Anaestetika Og Reontgenbestraaling. Saertryk Nord Med 83: 501-504.
Axelsson, G., and Rylander, R. 1982. Exposure to Anaesthetic
Gases and Spontaneous Abortion: Response Bias in a Postal Questionnaire
Study. Int J Epidemiol 11:
Azar, I., and Eisenkraft, J.B. 1993. Waste Asnesthetic
Gases Spillage and Scavenging Systems. In: Anesthetic Equipment:
Principles and Applications, Ehrenwerth, J., and Eisenkraft, J.B.,
editors, St. Louis, MO,
Baden, J.M., and Simmon, V.F. 1980. Mutagenic Effects of
Inhalation Anesthetics. Mutat Res 75:
Basford, A.B., and Fink, B.R. 1968. The Teratogenicity of
Halothane in the Rat. Anesthesiology 29:
Bowie, E., and Huffman, L.M. 1985. The Anesthesia Machine: Essentials for Understanding. Madison, WI: Ohmeda, The BOC Group, Inc.
Bruce, D.L.1991. Recantation Revisited. Anesthesiology
Bruce, D.L., Bach, M.J., and Arbit, J. 1974. Trace
Anesthetic Effects on Perceptual, Cognitive, and Motor Skills.
Bruce, D.L., and Bach, M.J. 1975. Psychological Studies of
Human Performance as Affected by Traces of Enflurane and Nitrous Oxide.
Bruce, D.L., and Stanley, T.H. 1983. Research Replication May Be Subject Specific. Anesth Analg 62: 617.
Buring, J.E., Hennekens, C.H., Mayrent, S.L., Rosner, B.,
Greenberg, E.R., and Colton, T. 1985. Health Experiences of Operating Room
Personnel. Anesthesiology 62:
Burkhart, J.E., and Stobbe, T.J. 1990.
Cohen, E.N., Bellville, J.W., and Brown, B.W., Jr. 1971.
Anesthesia, Pregnancy and Miscarriage. A Study of Operating Room Nurses
and Anesthetists. Anesthesiology 35:
Cohen, E.N., Brown, B.W., Wu, M.L., Whitcher, C.E., Brodsky,
J.B., Gift, H.C., Greenfield, W., Jones, T.W., and Driscoll, E.J. 1980.
Occupational Disease in Dentistry and Chronic Exposure to Trace Anesthetic
Gases. J Am Dent Assoc 101:
Corbett, T.H., Cornell, R.G., Endres, J.L., and Millard,
R.I. 1973. Effects of Low Concentrations of Nitrous Oxide on Rat
Pregnancy. Anesthesiology 39:
Corbett, T.H., Cornell, R.G., Endres, J.L., and Lieding, K.
1974. Birth Defects Among Children of Nurse Anesthetists.
Dorsch, J.A., and Dorsch, S.E. 1984. Understanding
Anesthesia Equipment. Second Edition. Baltimore, MD: Williams and
Dorsch, J.A., and Dorsch, S.E. 1994. Understanding Anesthesia Equipment: Construction, Care and Complications. Third Edition. Baltimore, MD: Williams and Wilkins. P.67.
Eichhorn, J.H. 1993. Anesthesia Equipment:Checkout and
Quality Assurrance. In: Anesthesia Equipment: Principles and
Applications. Ehrenwerth, J., and Eisenkraft, J.B., editors, St.
Emergency Care Research Institute. 1991. Technology for
Anesthesia. 12, No.
Fink, B.R., Shepard, T.H., and Blandau, R.J. 1967.
Teratogenic Activity of Nitrous Oxide. Nature 214:
Gandolfi, A.J., White, R.D., Sipes, I.G., and Pohl, L.R.
1980. Bioactivation and Covalent Binding of Halothane in Vitro: Studies
with [3H]- and [14C]
Halothane. J Pharmacol Exp Ther 214:
Garro, A.J., and Phillips, R.A. 1978. Mutagenicity of the
Guirguis, S.S., Pelmear, P.L., Roy, M.L., and Wong, L. 1990.
Health Effects Associated with Exposure to Anaesthetic Gases in Ontario
Hospital Personnel. Br J Ind Med 47:
Hallen, B., Ehrner-Samuel, H., and Thomason, M. 1970.
Measurements of Halothane in the Atmosphere of an Operating Theatre and in
Expired Air and Blood of the Personnel During Routine Anaesthetic Work.
Acta Anaesth Scand 14:
Henry, R.J., and Jerrell, R.G. 1990. Ambient Nitrous Oxide
Levels During Pediatric Sedations. Pediatr Dent 12:
Holmes, M.A., Weiskopf, R.B., Eger, E.I., Johnson, B.H., and
Rampil, I.J. 1990. Hepatocellular Integrity in Swine After Prolonged
Huffman, L.M. 1991. Common problems in waste gas management.
Jastak, J.T. 1989. Nitrous Oxide in Dental Practice. Int
Anesthesiol Clin 27:
Kestenberg, S.H., and Young, E.R. 1988. Potential Problems
Associated with Occupational Exposure to Nitrous Oxide. J Can Dent
Knill-Jones, R.P., Rodrigues, L.V., Moir, D.D., and Spence,
A.A. 1972. Anaesthetic Practice and Pregnancy: Controlled Survey of Women
Anaesthetists in the United Kingdom. Lancet 1:
Knill-Jones, R.P., Newman, B.J., and Spence, A.A. 1975.
Anaesthetic Practice and Pregnancy: Controlled Survey of Male
Anaesthetists in the United Kingdom. Lancet 2:
Lauwerys, R., Siddons, H., Misson, C.B., et al. 1981.
Anaesthetic Health Hazards Among Belgian Nurses and Physicians. Int
Arch Occup Environ Health 48:
McGlothlin, J.D., Jensen, P.A., Fischbach, T.J., Hughes,
R.T., and Jones, J.H. 1992. Control of Anesthetic Gases in Dental
Operatories. Scand J Work Environ Health 18 Suppl
National Institute for Occupational Safety and Health. 1977.
Criteria for a recommended standard: Occupational Exposure to Waste
Anesthetic Gases and Vapors. Cincinnati, OH: U.S.Department of Health,
Education, and Welfare. Public Health Service. Center for Disease Control.
National Institute for Occupational Safety and Health. DHEW (NIOSH)
__________. 1994. Control of Nitrous Oxide in Dental
Operatories. Cincinnati, OH: U.S.Department of Health and Human
Services. Public Health Service. Centers for Disease Control and
Prevention. National Institute for Occupational Safety and Health. DHHS
(NIOSH) Publication No.
Pharoah, P.O.D., Alberman, E., Doyle, P., and Chamberlain,
G. 1977. Outcome of Pregnancy Among Women in Anaesthetic Practice.
Popova, S., Virgieva, T., Atanasova, J., Atanasov, A., and
Sahatchiev, B. 1979. Embryotoxicity and fertility Study with Halothane
Subanesthetic Concentration in Rats. Acta Anaesth Scand. 23:
Purdham , J.T. 1986. Anesthetic Gases and Vapors (p86-21E). Hamilton, ON: Canadian Centre for Occupational Health and Safety.
Rosenberg, P., and Kirves, A. 1973. Miscarriages Among
Operating Theatre Staff. Acta Anaesth Scand Suppl 53:
Rosenberg, P.H., and Vanttinnen, H. 1978. Occupational
Hazards to Reproduction and Health in Anaesthetists and Paediatricians.
Acta Anaesth Scand 22:
Rowland, A.S., Baird, D.D., Weinberg, C.R., Shore, D.L.,
Shy, C.M., and Wilcox, A.J. 1992. Reduced Fertility Among Women Employed
as Dental Assistants exposed to High Levels of Nitrous Oxide. N Engl J
Rowland, A.S., Baird, D.D., Shore, D.L., Weinberg, C.R.,
Savitz, D.A., and Wilcox, A.J. 1995. Nitrous Oxide and Spontaneous
Abortion in Female Dental Assistants. Am J Epidemiol 141:
Smith, B.E., Gaub, M.L., and Moya, F. 1965. Teratogenic
Effects of Anesthetic Agents: Nitrous Oxide. Anesth Analg 44:
Smith, G., and Shirley, A.W. 1978. A Review of the Effects
of Trace Concentrations of Anaesthetics on Performance. Br J Anaesth
Sweeney, B., Bingham, R.M., Amos, R.J., Petty, A.C., and
Cole, P.V. 1985. Toxicity of Bone Marrow in Dentists Exposed to Nitrous
Oxide. Br Med J (Clin Res Ed) 291:
Tannenbaum, T.N., and Goldberg, R.J. 1985. Exposure to
Anesthetic Gases and Reproductive Outcome. J Occ Med 27:
Tomlin, P.J. 1979. Health Problems of Anaesthetists and
Their Families in the West Midlands. Br Med J 1:
United States Department of Labor, Occupational Safety and Health Administration. 1982. Record-keeping and Reporting Occupational Injuries and Illnesses. 29 CFR 1904. Washington, DC: United States Government Printing Office.
__________. 1990. Access to Employee and Medical Records Standard. 29 CFR 1910.1020. Washington, DC: United States Government Printing Office.
__________. 1994. Hazard Communication Standard. 29 CFR 1910.1200. Washington, DC: United States Government Printing Office.
__________. 1991. Chemical Information Manual. Washington, DC: United States Government Printing Office.
United States Food and Drug Administration, HHS. 1994.
Anesthesia Apparatus Checkout Recommendations, 1993; Availability.
Federal Register, 59(131):
Vaisman, A.I. 1967. Working Conditions in Surgery and Their
Effect on the Health of Anesthesiologists. Eksp Khir Anesteziol 3:
Wharton, R.S., Wilson, A.I., Mazze, R.I., Baden, J.M., and
Rice, S.A. 1979. Fetal Morphology in Mice Exposed to Halothane.
Weiskopf, R.B., Eger, E.I., 2d, Ionescu, P., Yasuda, N.,
Cahalan, M.K., Freire, B., Peterson, N., Lockhart, S.H., Ampil, I.J., and
Laster, M. 1992. Desflurane Does Not Produce Hepatic or Renal Injury in
Human Volunteers. Anesth and Analg 74:
American Conference of Governmental Industrial Hygienists (ACGIH) is an organization devoted to the development of administrative and technical aspects of worker health protection. The ACGIH is a professional organization, not a government agency.
ACGIH threshold limit
Adapters are fittings used to establish functional continuity between otherwise disparate and incompatible components.
Air is the elastic, invisible mixture of gases (chiefly nitrogen and oxygen) that may be used with medical equipment; also called medical air.
Anesthesia machine is equipment intended for dispensing and delivering anesthetic gases and vapors into a breathing system.
Anesthesia system is any of a variety of assemblies designed to administer an anesthetic.
Anesthetic agent is a drug that is used to reduce or abolish the sensation of pain, e.g., halothane, enflurane, isoflurane, desflurane, sevoflurane, and methoxyflurane.
Anesthetic agent vapor is the gaseous phase of an anesthetic agent that is normally a liquid at room temperature and atmospheric pressure.
Anesthetic gas is any gaseous substance, e.g., nitrous oxide, used in producing a state of anesthesia.
Anesthetic vaporizer is a device designed to facilitate the change of an anesthetic from a liquid to a vapor.
Anesthetizing location is any area in a facility where an anesthetic agent or drug is administered in the course of examination or treatment. This includes operating rooms, delivery rooms, emergency rooms, induction rooms, and other areas.
Area sample is a sample collected at a fixed point in the workplace. The data from the area sample may or may not correlate with an individual’s personal sample results due to the often high degree of variability in exposures.
Breathing system is a gas pathway in direct connection with the patient's lungs, through which gas flow occurs at respiratory pressures, and into which a gas mixture of controlled composition may be dispensed. The function of the breathing system is to convey oxygen and anesthetic gases to the patient's lungs and remove waste and anesthetic gases from the patient's lungs. Scavenging equipment is not considered part of the breathing system. The system is also referred to as breathing or patient circuit, respiratory circuit or system.
Breathing system, semiclosed is a system that allows some of the expired gases to leave the circuit; the remainder mixes with the fresh gases and is reinhaled. A CO2 absorber is used in this system.
Breathing tubes are
Breathing zone is defined as the area immediately adjacent to the employee’s nose and mouth; a hemisphere forward of the worker’s shoulders with a radius of approximately 6 to 9 inches.
Calibrated vaporizer is an instrument designed to facilitate the change of a liquid anesthetic into its vapor and to add a controlled amount of this vapor to the fresh gas flow.
Carbon dioxide (CO2) is a colorless, odorless gas, and is a normal end product of human metabolism. It is formed in the tissues and eliminated by the lungs.
Carbon dioxide absorber is a device used to remove CO2 chemically from exhaled patient gas. Primarily used in the closed or semiclosed circle breathing system, which requires carbon dioxide absorption to make reinhalation of previously exhaled gas possible.
Carcinogenicity is the ability of a substance to cause cancer.
Check valves are also known as unidirectional valves,
Common (fresh) gas outlet is the port through which the mixture of gases and vapors dispensed from the anesthesia machine is delivered to the breathing system. Also referred to as the machine outlet.
Compressed gas is defined as any material or mixture having in the container an absolute pressure exceeding 40 psig at 70°F or having an absolute pressure exceeding 104 psig at 130°F.
Congenital anomaly is a structural or functional abnormality of the human body that develops before birth but is not inherited. One type of birth defect.
Connectors are fittings intended to join together two or more components.
Cylinder supply source is a
Cylinder pressure gauge monitors the pressure of gas within a cylinder.
Diameter Index Safety System (DISS) provides threaded
Embryolethal refers to a substance that is lethal to the developing embryo, the product of conception up to the end of the eighth week of human pregnancy.
Epidemiology is the study of health and illness in human populations. It is the study of trends and events in similar populations, for example, one exposed to a chemical and one not exposed.
Excess gases are those gases and anesthetic vapors that are
delivered to the breathing circuit in excess of the patient’s requirements
and the breathing circuit’s capacity. These gases are released from the
breathing circuit via the APL or
Exhalation check valve, also known as expiratory unidirectional valve, refers to that valve placed in the vicinity of the CO2 absorber that ensures that exhaled gases flow away from the patient and into the absorber.
Flow control valve, also known as the needle valve, controls the rate of flow of a gas through its associated flow meter by manual adjustment of a variable orifice.
Flowmeter is a device that measures and indicates the flow rate of a gas passing through it.
Gas is defined as a formless fluid that expands readily to fill any containing vessel, and which can be changed to the liquid or solid state only by the combined effect of increased pressure and decreased temperature.
Gas-tight seal is a connection that does not allow bubbling when immersed in water and subjected to a differential pressure.
General anesthesia is a state of unconsciousness in which there is an absence of pain sensation.
Hanger yoke is a device used to attach a reserve gas cylinder to
the anesthesia machine. The functions of the hanger yoke are to orient and
support the cylinder, provide a
HVAC system, also known as the heating, ventilating, and air conditioning system, supplies outdoor replacement (make-up) air and environmental control to a space or building. It conditions the air by supplying the required degree of air cleanliness, temperature and/or humidity.
Inhalation check valve, also called inspiratory unidirectional valve, refers to the valve placed in the vicinity of the CO2 absorber that ensures that the gases flow toward the patient.
In vitro describes studies that are done in the laboratory, literally"in glass," using, for example, cells, as distinct from studies performed using whole living animals.
Medical gas is any gaseous substance that meets medical purity standards and has application in a medical environment. Examples are oxygen, nitrous oxide, helium, air, nitrogen, and carbon dioxide.
Medical gas mixture is a mixture of two or more medical gases to be used for a specific medical application.
Mutagenicity is the ability of a substance to cause changes in the genetic material.
NIOSH RELs (recommended exposure limits) are occupational
exposure limits recommended by NIOSH as being protective of worker health
and safety over a working lifetime. These limits are generally expressed
Nitrous oxide (N2O) is used as an anesthetic agent in medical, dental, and veterinary operatories. It is a weak anesthetic with rapid onset and rapid emergence. In hospitals, it may be used with oxygen as a carrier gas for other, more potent anesthetics. In dental offices, it is administered with oxygen, primarily as an analgesic (an agent that diminishes or eliminates pain in the conscious patient) and as a sedative to reduce anxiety.
Nonrecirculating ventilation system takes in fresh outside air and processes it by filtering and adjusting the humidity and temperature. The processed air is circulated through the various rooms in a facility, and then all of it is exhausted to the atmosphere. Whatever volume of fresh air is introduced into a room is ultimately exhausted outdoors.
Occupational exposure to waste anesthetic gases includes exposure to any inhalation anesthetic agents that escape into locations associated with, and adjacent to, anesthetic procedures. Such locations include, but are not limited to, operating rooms, delivery rooms, recovery rooms, and dental operatories.
Oxygen (O2) is an element which, at
atmospheric temperatures and pressures, exists as a colorless, odorless,
tasteless gas. Its utstanding properties are its ability to sustain life
and to support combustion. Although oxygen is nonflammable, materials
which burn in air will burn much more vigorously and create higher
temperatures in oxygen or
Oxygen flush valve is a separate valve designed to rapidly supply a large volume of oxygen to the breathing system.
PACU (postanesthesia care unit) is also known as the recovery room.
Patient end is the end of the component part nearest the patient.
PEEP valve is a device installed in the exhalation limb of the
patient circuit that allows positive
Personal sample is a sample collected from an individual’s breathing zone.
Pin Index Safety System is a safeguard to eliminate cylinder interchanging and the possibility of accidentally placing the incorrect gas on a yoke designed to accommodate another gas. Two pins on the yoke are so arranged that they project into the cylinder valve. Each gas or combination of gases has a specific pin arrangement.
Pipeline supply source is a permanently installed piped distribution system that delivers medical gases such as oxygen, nitrous oxide, and air to the operating room.
Pneumatic means pertaining to or operated by air or other gas under pressure.
Power outlet is an accessory outlet located on an anesthesia machine that supplies a driving gas for auxiliary equipment such as a ventilator. Driving gas is normally oxygen, but medical air may be used.
Pressure relief valve is a mechanical device that eliminates system overpressure by allowing the controlled or emergency escape of liquid or gas from a pressurized system. The relief valve may or may not be adjustable.
Prospective study or cohort study follows a population from a set time into the future. It is an epidemiological method for identifying the future relationship, if any, between exposure to an agent and the increased incidence of some adverse health effect in a population.
PSIG stands for pounds per square inch gauge, which is the difference between the measured pressure and surrounding atmospheric pressure. Most gauges are constructed to read 0 at atmospheric pressure.
Recirculating ventilation system returns part of the exhaust air to the air supply duct. The system takes in an amount of fresh outside air that varies as a function of the outside temperature. Air exhausted from a room is filtered for particulate matter and bacteria, not anesthetic gases, and then recirculated through several rooms by means of a common mixing (plenum) chamber. In this process, some fresh air is added and a equal amount of recirculating air is exhausted.
Recovery room is the patient care location where recovering patients are awakened and stabilized and/or awakened after surgical anesthesia. Anesthetic gases are exhaled by recovering patients (who received inhalation anesthetics) as they breathe.
Reservoir bag is also known as the respiratory bag or breathing bag. It allows accumulation of gas during exhalation so that a reservoir is available for the next inspiration. It provides a means whereby anesthesia personnel may assist or control ventilation. It can serve, through visual and tactile observation, as a monitor of a patient’s spontaneous respirations and acts to protect the patient from excessive pressure in the breathing system.
Respiration is the process by which a rapid exchange of oxygen and carbon dioxide takes place between the atmosphere and the blood coming to the pulmonary capillaries. Oxygen is taken up, utilized in metabolic processes, and a proportional amount of carbon dioxide is released.
Retrospective study or case control study examines two populations. The first population consists of individuals who demonstrate the effect of interest, and the second is made up of those who do not. The two populations are matched as well as possible with respect to all other variables, e.g., age, socioeconomic status, and so on. Then the past histories of exposure of the two populations are investigated to determine if some differences can be identified that might be related to the toxic effects observed.
Scavenging is defined as the collection of excess gases from the breathing circuit and removal of these gases to an appropriate place of discharge outside the working environment.
Scavenging system is defined as a device (assembly of specific
components) that collects and removes the excess anesthetic gases that are
released from the breathing circuit. Scavenging systems are also called
evacuation systems, waste anesthetic gas disposal systems, and excess
Source-control technology is an engineering control designed to collect and remove excess anesthetic gases at the point of origin (i.e., from the breathing circuit or in close proximity to the patient’s mouth and nose). It can be either a scavenging system or local (auxiliary) exhaust ventilation system.
Source sample is a sample collected at the origin of contamination (source of emission).
Teratogenicity is the ability of a substance to cause birth defects in offspring, as a result of maternal (before or after conception) or paternal exposure to the toxic substance.
Tracheal tube also called the endotracheal tube, intratracheal tube, and catheter is inserted into the trachea and is used to conduct gases and vapors to and from the lungs.
TWA is a
Unidirectional valve is a valve that allows gas flow in one direction only. Two unidirectional valves are used in each circle system to ensure that the gases flow toward the patient in one limb of the circle breathing system and away in the other. They are usually part of the absorber assembly.
Vapor is the gaseous phase of a substance which at ordinary temperature and pressure exists as a liquid.
Ventilation is (1) the physical process of moving gases into and out of the lungs. (2) It is also defined for the purposes of industrial hygiene engineering as a method for providing control of an environment by strategic use of airflow. The flow of air may be used to provide either heating or cooling of a work space, to remove a contaminant near its source of release into the environment, to dilute the concentration of a contaminant to acceptable levels, or to replace air exhausted from a space.
Waste anesthetic gases are those gases that are inadvertently released into the workplace and/or can no longer be used. They include all fugitive anesthetic gases and vapors that are released into anesthetizing and recovery locations, from equipment used in administering anesthetics under normal operating conditions, as well as those gases that leak from the anesthetic gas scavenging system, or are exhaled by the patient into the workplace environment. Waste gases are also those excess gases in the breathing circuit that are ultimately scavenged. Spills of liquid anesthetic agents also contribute to ambient levels of waste gases. Waste anesthetic gases may include N2O and vapors of potent inhaled volatile anesthetic agents such as halothane, enflurane, isoflurane, desflurane and sevoflurane.
This checkout, or a reasonable equivalent, should be conducted before administration of anesthesia. These recommendations are only valid for an anesthesia system that conforms to current and relevant standards and includes an ascending bellows ventilator and at least the following monitors: capnograph, pulse oximeter, oxygen analyzer, respiratory volume monitor (spirometer) and breathing system pressure monitor with high and low pressure alarms. This is a guideline which users are encouraged to modify to accommodate differences in equipment design and variations in local clinical practice. Such local modifications should have appropriate peer review. Users should refer to the operator’s manual for the manufacturer’s specific procedures and precautions, especially the manufacturer’s low pressure leak test (step #5).
Note: *If an anesthesia provider uses the same machine in successive cases, these steps need not be repeated or may be abbreviated after the initial checkout.
Emergency Ventilation Equipment
*1. Verify Backup Ventilation Equipment is Available & Functioning
*2. Check Oxygen Cylinder Supply
- Open O2 cylinder and verify at least half full (about 1000 psi).
- Close cylinder.
*3. Check Central Pipeline Supplies
- Check that hoses are connected and pipeline gauges read about 50 psi.
*4. Check Initial Status of
- Close flow control valves and turn vaporizers off.
- Check fill level and tighten vaporizer’s filler caps.
*5. Perform Leak Check of Machine
- Verify that the machine master switch and flow control valves are OFF.
- Attach"Suction Bulb" to common (fresh) gas outlet.
- Squeeze bulb repeatedly until fully collapsed.
- Verify bulb stays fully collapsed for at least 10 seconds.
- Open one vaporizer at a time and repeat"c" and"d" as above.
- Remove suction bulb, and reconnect fresh gas hose.
* 6. Turn On Machine Master Switch and all other necessary equipment.
* 7. Test Flowmeters
- Adjust flow of all gases through their full range, checking for smooth operation of floats and undamaged flowtubes.
- Attempt to create a hypoxic O2/N2O mixture and verify correct changes in flow and/or alarm.
* 8. Adjust and Check Scavenging System
- Ensure proper connections between the scavenging system and both APL
(pop-off)valve and ventilator relief valve.
- Adjust waste gas vacuum (if possible).
- Fully open APL valve and occlude Y-piece.
- With minimum O2 flow, allow scavenger reservoir bag to collapse completely and verify that absorber pressure gauge reads about zero.
- With the O2 flush activated, allow the scavenger reservoir bag to distend fully, and then verify that absorber pressure gauge reads <10 cm H2O.
* 9. Calibrate O2 Monitor
- Ensure monitor reads 21% in room air.
- Verify low O2 alarm is enabled and functioning.
- Reinstall sensor in circuit and flush breathing system with O2.
- Verify that monitor now reads greater than 90%.
10. Check Initial Status of Breathing System
- Set selector switch to"Bag" mode.
- Check that breathing circuit is complete, undamaged and unobstructed.
- Verify that CO2 absorbent is adequate.
- Install breathing circuit accessory equipment (e.g., humidifier, PEEP valve) to be used during the case.
11. Perform Leak Check of the Breathing System.
- Set all gas flows to zero (or minimum).
- Close APL (pop-off) valve and occlude Y-piece.
- Pressurize breathing system to about 30 cm H2O with O2 flush.
- Ensure that pressure remains fixed for at least 10 seconds.
- Open APL (pop-off) valve and ensure that pressure decreases.
Manual and Automatic Ventilation Systems
12. Test Ventilation Systems and Unidirectional Valves
- Place a second breathing bag on Y-piece.
- Set appropriate ventilator parameters for next patient.
- Switch to automatic ventilation (Ventilator) mode.
- Fill bellows and breathing bag with O2 flush and then turn ventilator ON.
- Set O2 flow to minimum, other gas flows to zero.
- Verify that during inspiration bellows delivers appropriate tidal volume and that during expiration bellows fills completely.
- Set fresh gas flow to about 5 L/min.
- Verify that the ventilator bellows and simulated lungs fill and empty appropriately without sustained pressure at end expiration.
- Check for proper action of unidirectional valves.
- Exercise breathing circuit accessories to ensure proper function.
- Turn ventilator OFF and switch to manual ventilation (Bag/APL) mode.
- Ventilate manually and assure inflation and deflation of artificial lungs and appropriate feel of system resistance and compliance.
- Remove second breathing bag from Y-piece.
13. Check, Calibrate and/or Set Alarm Limits of all Monitors
Pressure Monitor with High and Low Airway Alarms
Respiratory Volume Monitor (Spirometer)
14. Check Final Status of Machine
- Vaporizers off
- APL valve open
- Selector switch to"Bag"
- All flowmeters to zero
- Patient suction level adequate
- Breathing system ready to use
The interface serves to prevent potentially dangerous increases or decreases of pressure in the anesthetic waste gas disposal system from reaching the patient’s breathing circuit. In order to do this, the interface has three components: positive pressure relief, negative pressure relief, and a reservoir.
Irrespective of the type of disposal system used (i.e., active or
passive), positive pressure relief must be provided to protect the
equipment and patient if occlusion of the scavenging system outlet occurs.
If the scavenging system outlet becomes occluded, the
Interfaces can be divided into two types: open and closed, depending on
the means to provide positive and negative pressure relief. An open
reservoir interface is one that is always open to atmosphere and contains
no valves. It relies on open ports for positive and negative pressure
relief. A closed interface uses
The open reservoir interface (Figure 9) should be used only with an
active disposal system. Because the discharge of waste gases from the
breathing system is usually intermittent and flow through an active
disposal assembly is continuous, a reservoir is needed to accommodate the
surges of gas that enter the interface at a flow rate greater than that at
which the disposal system removes them. The reservoir allows the flow rate
in the disposal system to be kept just above the average, rather than at
the peak flow rate of gases from the
A closed interface is one in which the connection(s) with the atmosphere is(are) through valve(s). A positive pressure relief is always required to allow release of gases into the room if there is an obstruction of the scavenging system downstream of the interface. If an active disposal system is to be used, a negative pressure relief valve is necessary to allow entrainment of room air when the pressure falls below atmospheric.
Figure 9. Open reservoir scavenging interface. Reproduced by permission of North American Dräger, Telford, Pennsylvania).
The interface typically consists of a manifold with four ports and two relief valves (Azar and Eisenkraft 1993; Dorsch and Dorsch 1994). Figure 10 shows the flow of waste gases from the breathing circuit as it enters the intake ports of the interface. This figure shows the pathway of gas flow in an active scavenging system that uses a facility’s vacuum source (wall suction) for gas disposal (Huffman 1991).
As gas is drawn through the suction nipple, located on the right of the
drawing in Figure
10, it flows through the manifold and past the two relief valves. The
upper relief valve limits positive pressure, and the lower valve limits
negative pressure. A
The rate of gas flow through the interface is controlled by adjusting
the needle valve in such a way that the reservoir bag is not allowed to
become filled. In the ideal situation, this rate of flow should maintain
the volume in the reservoir bag between empty and
The purpose of these valves is to protect the breathing circuit from extremes of pressure. The positive pressure relief valve will not be activated if the flow is properly adjusted and the contour of the bag is observed to monitor its volume. In an active scavenging system, any unused nipple must be capped or the vacuum will draw in room air and also provide the opportunity for waste gases to diffuse into the room.
Figure 10. The flow of waste gases through the scavenging interface that is connected to a vacuum source. (Reproduced by permission of Datex·Ohmeda, Madison, Wisconsin).
A passive scavenging system for waste gas evacuation, shown in Figure 11, uses the facility’s ventilation system instead of the vacuum system to dispose of waste gases. In this configuration, flow of waste gases through the interface is basically the same as in the active system. Gas pressure is limited by positive and negative relief valves. Transfer of the waste gases from the interface to the disposal system relies solely on the pressure of the waste gases since a vacuum is not used.
In a passive system the adjustment knob must remain in the down position to close the needle valve. As shown below, a 19 mm corrugated hose is used to connect the interface with the room’s ventilation exhaust grille (Azar and Eisenkraft 1993). A passive system (unlike an active system) is not connected to a vacuum or source of negative pressure and does not need to be adjusted regularly.
Figure 11. The flow of waste gases through the interface in a passive scavenging system.
(Reproduced by permission of Datex·Ohmeda, Madison, Wisconsin).