ANESTHETIC GASES:
|
Generic
or |
Commercial
name |
Year
of |
Currently |
Diethyl
ether |
Ether |
1842 |
No |
Nitrous
oxide |
Nitrous
oxide |
1844 |
Yes |
Chloroform |
Chloroform |
1847 |
No |
Cyclopropane |
Cyclopropane |
1933 |
No |
Trichloroethylene |
Trilene® |
1934 |
No |
Fluroxene |
Fluoromar® |
1954 |
No |
Halothane |
Fluothane® |
1956 |
Yes |
Methoxyflurane |
Penthrane® |
1960 |
Infrequently |
Enflurane |
Ethrane® |
1974 |
Yes |
Isoflurane |
Forane® |
1980 |
Yes |
Desflurane |
Suprane® |
1992 |
Yes |
Sevoflurane |
Ultane® |
1995 |
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
Rowland 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 1986; Kestenberg 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 1967; Askrog 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.
1.
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 the machine
Figure 1. The flow
arrangement of a basic
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
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 incorporates a
2.
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
3.
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
Several
Occupational
exposures can be controlled by the application of a number of
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 rooms and
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.
Active Systems
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
Passive Systems
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 the
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
G -
·
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.
4.
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
During
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'
·
Any
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.
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
a.
Engineering Controls
Waste gas evacuation is required for every
type of breathing circuit configuration (Huffman 1991; Azar 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 (Dorsch 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
b.
Work Practices
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).
2.
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
a.
Engineering Controls
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
b.
Work Practices
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.
a.
Engineering Controls
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
b.
Work Practices
·
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 mask,
4.
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, greater
a.
Engineering
Controls
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 [
b.
Work
Practices
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
·
Occlude
the
·
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 requires high
·
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 predictable
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
·
Wear
appropriate personal protective equipment. (Refer to section E. 4. on personal
protective equipment).
·
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.
a.
Nitrous
Oxide
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.
b.
Halogenated
Agents
Three
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.
3.
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 (i.e.,
·
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),
employers in
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
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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.
Adjustable
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 noninterchangeable
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 as
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 anesthetic
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
High-Pressure System
*2. Check Oxygen Cylinder Supply
a. Open O2 cylinder and verify at least half full (about 1000 psi).
b. Close
cylinder.
*3. Check Central Pipeline
Supplies
a. Check that
hoses are connected and pipeline gauges read about 50 psi.
Low-Pressure System
*4. Check Initial Status of
a. Close flow
control valves and turn vaporizers off.
b. Check fill
level and tighten vaporizer’s filler caps.
*5. Perform Leak Check of Machine
a. Verify that
the machine master switch and flow control valves are OFF.
b. Attach"Suction
Bulb" to common (fresh) gas outlet.
c. Squeeze bulb
repeatedly until fully collapsed.
d. Verify bulb
stays fully collapsed for at least 10 seconds.
e. Open one
vaporizer at a time and repeat"c" and"d" as above.
f. Remove suction
bulb, and reconnect fresh gas hose.
* 6. Turn On Machine Master Switch and all other necessary
equipment.
* 7. Test Flowmeters
a. Adjust flow of
all gases through their full range, checking for smooth operation of floats
and undamaged flowtubes.
b. Attempt to
create a hypoxic O2/N2O mixture and verify correct changes in flow and/or alarm.
Scavenging System
* 8. Adjust and Check Scavenging
System
a. Ensure proper
connections between the scavenging system and both APL
b. Adjust waste
gas vacuum (if possible).
c. Fully open APL
valve and occlude Y-piece.
d. With minimum O2 flow, allow scavenger reservoir bag to collapse completely and verify
that absorber pressure gauge reads about zero.
e. With the O2 flush activated, allow the scavenger reservoir bag to distend fully,
and then verify that absorber pressure gauge reads <10 cm H2O.
Breathing System
* 9. Calibrate O2 Monitor
a. Ensure monitor
reads 21% in room air.
b. Verify low O2 alarm is enabled and functioning.
c. Reinstall
sensor in circuit and flush breathing system with O2.
d. Verify that
monitor now reads greater than 90%.
10. Check Initial Status of
Breathing System
a. Set selector
switch to"Bag" mode.
b. Check that
breathing circuit is complete, undamaged and unobstructed.
c. Verify that CO2 absorbent is adequate.
d. Install
breathing circuit accessory equipment (e.g., humidifier, PEEP valve) to be
used during the case.
11. Perform Leak Check of the
Breathing System.
a. Set all gas
flows to zero (or minimum).
b. Close APL
(pop-off) valve and occlude Y-piece.
c. Pressurize
breathing system to about 30 cm H2O with O2 flush.
d. Ensure that
pressure remains fixed for at least 10 seconds.
e. Open APL
(pop-off) valve and ensure that pressure decreases.
Manual and Automatic Ventilation
Systems
12. Test Ventilation Systems and
Unidirectional Valves
a. Place a second
breathing bag on Y-piece.
b. Set
appropriate ventilator parameters for next patient.
c. Switch to
automatic ventilation (Ventilator) mode.
d. Fill bellows
and breathing bag with O2 flush and then turn
ventilator ON.
e. Set O2 flow to minimum, other gas flows to zero.
f. Verify that
during inspiration bellows delivers appropriate tidal volume and that during
expiration bellows fills completely.
g. Set fresh gas
flow to about 5 L/min.
h. Verify that
the ventilator bellows and simulated lungs fill and empty
appropriately without sustained pressure at end expiration.
i. Check for
proper action of unidirectional valves.
j. Exercise
breathing circuit accessories to ensure proper function.
k. Turn
ventilator OFF and switch to manual ventilation (Bag/APL) mode.
l. Ventilate
manually and assure inflation and deflation of artificial lungs and
appropriate feel of system resistance and compliance.
m. Remove second
breathing bag from Y-piece.
Monitors
13. Check, Calibrate and/or Set
Alarm Limits of all Monitors
Capnometer
Oxygen Analyzer
Pressure Monitor with High and Low Airway Alarms
Pulse Oximeter
Respiratory Volume Monitor (Spirometer)
Final Position
14. Check Final Status of Machine
a. Vaporizers off
b. APL valve open
c. Selector
switch to"Bag"
d. All flowmeters
to zero
e. Patient
suction level adequate
f. 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).