THE AMERICAN COLLEGE OF VETERINARY ANESTHESIOLOGISTS
Commentary and recommendations on control of waste anesthetic
gases in the workplace
Health Hazards
Conflicting evidence exists in the scientific literature about
the effects of trace levels of anesthetic gases on the health
and performance of operating room personnel. Genetic mutations,
cancer, complications during pregnancy (eg, spontaneous abortions),
hepatic and renal disease, immunological effects, and psychomotor
changes have been linked to exposure to trace gases. In most instances,
definitive proof is lacking.
Even though potential for serious effects on human health
and performance in the operating room is probably small, exposure
to waste anesthetic gases should not be ignored.
Potential hazards exist for all personnel exposed to trace
gases-not just women of childbearing age. Thus, measures to control
waste gases should be directed to protect all personnel, not a
select group.
Any veterinary facility using inhalant anesthetics (ie,
halogenated hydrocarbons and/or nitrous oxide) should institute
and maintain a control program for waste anesthetic gases, based
on the possibility that trace gases may adversely affect human
health.
General Techniques and Procedures for Decreasing Pollution
Anesthesia machines, ventilators, breathing systems, and waste-gas
scavenging systems may contribute to environmental pollution with
waste anesthetic gases. Appropriate checkout methods and routine
maintenance for such equipment should be standard operating procedures
for veterinary facilities that use inhalant anesthetics.
Elimination of the following habits or techniques will decrease
anesthetic gas pollution when inhalant anesthetics are used:
Administering inhalant anesthetics by open drop (eg, periodically
dripping liquid volatile anesthetic onto a gauze sponge) or insufflation
(eg, delivery of a relatively high flow of anesthetic in oxygen
into the trachea or pharynx through a catheter) techniques. If
used, such techniques should be conducted in a fume hood.
Turning on flowmeters and vaporizers before attaching the
breathing system to the patient.
Allowing flowmeters and vaporizers to remain on after the
patient is disconnected from the breathing system.
Using uncuffed endotracheal tubes that do not create a completely
sealed airway or using cuffed tubes without inflating the cuff.
Disconnecting a patient from a breathing system without eliminating
as much of the residual gases as reasonably possible through the
scavenging system. Systems should be flushed with oxygen (eg,
empty the breathing bag through the pop-off valve periodically
after the vaporizer has been turned off and employ an increased
flow rate of oxygen [2-3 times maintenance flow] during recovery
for circle breathing systems). The patient should remain attached
- to the breathing system until extubation occurs.
Spilling liquid anesthetic during the filling of vaporizers,
especially during an anesthetic procedure. Ideally, properly functioning,
agent-specific, keyed filler systems should be used, and at a
minimum, a bottle adapter with a spout to prevent excessive spillage
should be used. Routinely filling vaporizers at the end of the
workday as personnel are leaving the hospital for the night should
reduce exposure to waste gases.
The use of masks and closed containers for delivery of inhalant
anesthetics should be minimized. If employed, these techniques
should be used in well ventilated rooms with nonrecirculating
ventilation systems or under a fume hood.
Scavenging systems should be used with all inhalant anesthesia
delivery systems to which they are adaptable. Unscavenged delivery
systems should not be used except as described previously.
The lowest fresh-gas flow rates, consistent with the proper
function of flowmeters, vaporizers, and breathing systems and
with patient safety, should be used (as opposed to very high fresh-gas
flows). Although scavenging systems should function effectively
for both high and low fresh-gas flows, low flows produce less
waste gases. From the global perspective, low fresh-gas flow rates
are consistent with protection of the earth's environment.
Routine filling of vaporizers should be performed with few
people in the room and in a well-ventilated area. Filling vaporizers
under a ceiling-mounted hood with an active evacuation system
is ideal. Agent specific, keyed filler ports for vaporizers and
corresponding keyed bottle adapters are available. Keyed bottle
adapters with spouts should be employed to prevent excess spillage
of anesthetic during the filling of vaporizers with screw-cap
filler ports.
Scavenging Systems
The use of scavenging devices with anesthesia delivery systems
is the most effective way to decrease waste anesthetic gases;
an efficient scavenging system is capable of reducing ambient
concentrations of waste gases by up to 90%. Anesthesia machines
and breathing systems delivering halogenated hydrocarbon anesthetics
and/or nitrous oxide should not be operated unless they are equipped
with a functional scavenging system.
To be effective, a scavenging system must not leak and must
control the concentration of trace anesthetics in ambient air.
Waste gases should not be discharged into the outside air in an
area where reentry into the building is likely.
Although some variations exist, a scavenging system consists
of a gas collecting device (eg, a scavenging pop-off or overflow
valve), transfer tubing, an interface, additional transfer tubing,
and a gas disposal system. Both passive and active scavenging
systems are effective if set up and used properly.
Passive systems that simply vent gases to floor level and
rely on inhalant anesthetic gases being heavier than air are unacceptable.
Nonrecirculating room-ventilation systems, which provide 12
to 15 air changes/h, can be used for waste-gas disposal by routing
transfer tubing to an exhaust grille. In addition, a nonrecirculating
room-ventilation system is an excellent adjunct to a scavenging
system to reduce the concentration of waste gases that are inadvertently
discharged into the room (eg, breathing system disconnect).
Recovery rooms can be polluted with significant amounts of
waste gases (eg, gases exhaled by the patient after disconnection
from the breathing system). Anesthesia machines with functional
scavenging systems should be used as long as feasible in patients
recovering from inhalant anesthesia. The breathing system should
be flushed with oxygen and the reservoir bag expressed into the
scavenging system before the endotracheal tube cuff is deflated
or the breathing system is disconnected. Ideally, recovery rooms
should have nonrecirculating ventilation systems with a high rate
of air exchange.
Facilities that utilize open-delivery systems that preclude
the use of standard scavenging devices to control waste gases
should allow use of such techniques only under a fume hood or
similar system that allows rapid elimination of waste gases from
the workplace.
Masks with activated charcoal filters can be used by operating
room personnel who are at special risk (eg, pregnancy) with regard
to exposure to inhalant anesthetics (except nitrous Oxide).
Canisters containing activated charcoal can be used as waste-gas
disposal systems in lieu of other types of scavenging systems,
especially when portability is an issue. However, some variation
in effectiveness occurs with different brands of canisters and
with changes in the rate of gas flow through the canister. Activated
charcoal is not effective for adsorption of nitrous oxide. Adsorption
methods of scavenging are recommended only if other more reliable
techniques are not available.
Evaluation of Anesthetic Equipment
One of the most important sources of waste anesthetic gases
is inhalant anesthetic equipment. Anesthesia machines and ventilators,
breathing systems, and scavenging systems should be checked and
maintained to assure that they do not leak anesthetics into the
atmosphere of the workplace.
The routine maintenance procedures for anesthetic equipment
are usually explained in the operations manuals. Many anesthesia
textbooks include guidelines for checkout of machines, breathing
systems, ventilators, and scavenging systems. The specifics of
these evaluations are too extensive for this report. However,
each piece of equipment involved in the delivery of inhalant anesthetics
should be evaluated regularly to assure its function and integrity.
Each veterinarian should become familiar with checkout and
maintenance procedures for the anesthesia equipment that he or
she uses. It is his or her responsibility to learn such procedures,
either by reading the appropriate operations manuals and textbooks
or by consulting an expert.
The Occupational Safety and Health Administration (OSHA) can
require that checkout and maintenance procedures for anesthetic
equipment be logged into a permanent record. Ideally a log of
evaluation and maintenance procedures and leakage testing should
be maintained for each anesthesia machine, ventilator, and vaporizer.
Checkout procedures are important prior to the use of anesthesia
equipment, and personnel operating anesthesia equipment should
be trained to complete checkout procedures and to recognize indications
of equipment malfunction.
Procedures for checkout of anesthesia equipment, depending
on the equipment to be used, should include the following:
Status of the high-pressure system, including the oxygen
supply (cylinder and central pipeline) and nitrous oxide supply
- The nitrous oxide supply should not leak when the cylinder
valve is on and the nitrous oxide flowmeter is off.
Status of the low-pressure system (flowmeter function and
evaluation for leaks in the low-pressure system) - A negative-pressure
leak test should be performed at the common gas outlet or the
outlet of the vaporizer immediately upstream from the breathing
system.
Status of the breathing system (including the condition
of chemical absorbent for carbon dioxide, leak tests, and function
of the pop-off or overflow valve and one-way valves) - The
status of the breathing system should be checked before using
the system on each patient. An appropriate leak test for a circle
system is to close the pop-off valve, occlude the Y-piece, pressurize
the system to 30 cm of h3O with all flowmeters off, and ensure
that the pressure does not decrease for at least 10 seconds. Noncircle
systems can usually be checked for leaks by applying positive
pressure to the system with all ports occluded, with similar guidelines
as for circle systems. The quantity of leakage can be measured
by determining the flow rate of oxygen necessary to maintain a
constant pressure in the system, and the leak rate should be less
than 300 ml/min at 30 cm of h3O.
Status of the scavenging system - The scavenging system
should be properly attached at all connectors, and the appropriate
vacuum should be assured for active systems. If charcoal canisters
are employed for scavenging, they should be changed at appropriate
intervals, according to the directions of the manufacturer.
Status of mechanical ventilators - Ventilators should
be connected properly to the anesthesia machine, and an absence
of leaks should be assured. Ventilators with an inverted bellows
should fill completely (rise to the top of the housing) during
expiration, and ventilators with hanging bellows should not fall
if the patient port is occluded at the end of inspiration.
Monitoring of the Effectiveness of Antipollution Techniques
Monitoring trace-gas concentrations in the workplace provides
a quantitative assessment of the effectiveness of a waste-gas
control program. Measuring the concentration of anesthetic in
the breathing zone of the most heavily exposed workers is the
usual procedure. Currently, no regulations require a veterinary
hospital to measure waste-gas concentrations regularly However,
under the "general duty clause," an employer is required
to provide a reasonably safe working environment for all employees.
In the United States, OSHA requires individual veterinary
hospitals and practices to maintain a system to prevent waste
gases from building up in the area of use and can enforce exposure
limits that are consistent with recommendations offered by the
National Institute of Occupational Safety and Health (NIOSH).
The NIOSH recommends that the maximum time-weighted average concentration
of volatile halogenated anesthetics should not exceed 2 ppm when
used alone or 0.5 ppm when used with nitrous oxide and that nitrous
oxide concentration should not exceed 25 ppm.
An accredited industrial hygiene laboratory is a source for
assistance in establishing an air-monitoring program. Such laboratories
are capable of sampling the air in the workplace and assaying
such samples for inhalant anesthetics. Industrial hygienists can
be found in the yellow pages of the telephone directory under
"occupational safety."
An air-monitoring program is most appropriately started after
anesthesia delivery systems have been equipped with scavenging
systems and after other techniques for minimizing waste gas pollution
are in place. An ideal approach would include frequent air monitoring,
preferably at least semiannual evaluations.
Commercial companies offer personal monitoring systems (badges
to be worn by individual workers) for the detection of nitrous
oxide and halogenated inhalant anesthetics. Purchase of the monitoring
badges may include prepaid laboratory analyses. Companies supplying
these badges claim to accurately detect concentrations in the
range of those recommended by NIOSH. Such monitoring has been
recommended for veterinary practices.
Use of a portable infrared analyzer for detection of anesthetic
gases has been proposed as a way for veterinary practices to monitor
the environment of the workplace. Such a method might be economical
if the monitor were shared by multiple practices.
After establishing procedures for control of anesthetic
gases, the logical next step for veterinary clinics, hospitals,
laboratories, and other institutions is the development of a consistent
monitoring program for waste gases that is suitable, both qualitatively
and economically, for the particular type of practice.
From the American College of Veterinary, Anesthesiologists
(ACVA). Members of the ACVA ad hoc Committee on Waste Anesthetic
Gas Pollution and Its Control were Drs. Janyce Cornick-Seahorn,
Sophie Cuvelliez, Jamie Gaynor, Charles McGrath, and Sandee Hartsfield
(chairman).
Address correspondence to Dr. Hartsfield at the Department
of Small Animal Medicine and Surgery, College of Veterinary Medicine,
Texas A&M University, College Station, TX 77843-4474.
