Anesthetic
Gases: Guidelines for
Workplace Exposure
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:
open-insufflation, semiopen
without nonrebreathing
valves, semiopen with
nonrebreathing valves,
semiclosed, and closed.
Figure 8 illustrates a
circle breathing system.
Oxygen and anesthetic are
transported to the animal’s
lungs from the anesthesia
machine through a face mask
or tracheal tube. An
inflatable cuff on the
distal end of the tracheal
tube facilitates a seal with
the inner wall of the
trachea.
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
fresh-gas flows are
typically used with all
techniques except
closed-system breathing
circuits. During expiration,
excess or waste gas exits
the breathing circuit at the
adjustable pressure-limiting
(APL) or pop-off valve and
escapes into the room unless
it is appropriately
scavenged.
Non-rebreathing systems
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
fresh-gas flows are required
to ensure removal of carbon
dioxide from the system. A
higher fresh-gas flow may
lead to an increase in
ambient waste gas levels.
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 pop-off valve is
connected to the scavenging
interface valve. A waste gas
reservoir bag is attached to
the interface valve and
collects excess anesthetic
gases.
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 [15-17]
of this document. A vacuum
source, if present, is
connected to the interface
valve and waste gas
reservoir bag, where gas is
stored until the vacuum can
move it to the outside air.
If only halogenated
compounds are used, an
activated charcoal
adsorption system can be
used.
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
positive-pressure breath
while the APL or pop-off
valve is closed and
listening for a leak
originating from around the
tracheal tube cuff.
•Occlude the Y-piece if
the breathing circuit must
be disconnected during
surgery.
•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 administernon-anesthetic
gases/agents as long as
clinically necessary, using
high oxygen flow rates
through the breathing
circuit to wash the
anesthetic gases out of the
system and the animal. This
allows exhaled anesthetic
gases to be collected by the
scavenging system.
•It is possible to close
an anesthetic circle and
reduce fresh-gas flow rates.
In a circle system where
oxygen is the only carrier
gas, the amount of fresh gas
flowing to the animal should
be adjusted to closely match
the animal’s metabolic
oxygen requirement.
•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 gas-flow
rates, with substantial
anesthetic spillage. Methods
to minimize this spillage
include tight seals on the
box and placement of the box
near the ventilation port of
a well-ventilated room. The
box can also be connected to
an anesthetic gas-scavenging
system to evacuate the gases
in the box prior to removing
the animal.
•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
gas-specific fittings.
G. CLEAN-UP AND DISPOSAL OF
LIQUID ANESTHETIC AGENT
SPILLS
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
worst-case scenario, and
plan response procedures
accordingly. Only adequately
trained and equipped workers
may respond to spills. When
the situation is unclear or
data are lacking on the
exposure level, the response
needs to be the same as for
high levels of exposure.
Responses to incidental
releases of liquid
anesthetic agents where the
substance can be absorbed,
neutralized, or otherwise
controlled at the time of
release by employees in the
immediate release area, or
by maintenance personnel do
not fall within the scope of
this standard.
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 clean-up of organic
chemicals. "Spill pillows"
commonly used in hospital
laboratories, vermiculite,
and carbon-based sorbents
are some of the materials
commercially available and
regularly used for this
purpose. Caution should be
exercised if broken glass
bottles pose a hazard.
Both enflurane and
desflurane are considered
hazardous wastes under the
EPA regulations because
these chemicals contain
trace amounts of chloroform
(a hazardous substance), a
by-product of the
manufacturing process.
Consequently, sorbents that
have been saturated with
enflurane or desflurane
should be managed as an EPA
hazardous waste material due
to the trace concentrations
of chloroform present.
Isoflurane and halothane do
not contain trace amounts of
chloroform or any other
regulated substance and are
therefore not considered
hazardous wastes by EPA.
To minimize exposure to
all liquid anesthetic agents
during clean-up and to limit
exposure during disposal
procedures, the following
general guidelines are
recommended. The waste
material should be placed in
a container, tightly sealed,
properly labeled, and
disposed of with other
chemical wastes sent to a
facility’s incinerator or
removed by a chemical waste
contractor. After a large
spill has occurred and the
appropriate response action
taken, airborne monitoring
should be conducted to
determine if the spill was
effectively contained and
cleaned up.
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 clean-up and
disposal, the following
general guidelines are
recommended by the
manufacturers of liquid
anesthetic agents: Wear
appropriate personal
protective equipment. (Refer
to section E4 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 clean-up is
complete.
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.
H. AIR MONITORING
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 health-care
environment. The data
provided by monitoring are
necessary to establish
proper engineering, work
practice, and administrative
controls to ensure the
lowest reasonably achievable
gas levels in the operatory
and PACU room air.
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
check-out procedures for
anesthesia equipment, and
education to ensure use of
appropriate work practices.
It does not believe that a
routine monitoring program
is necessary when these
actions are being carried
out. ASA prefers to
use monitoring when
indicated such as in the
event of known or suspected
equipment malfunction. The
Academy of General Dentistry
also emphasizes properly
installed and maintained
analgesia delivery systems.]
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
time-weighted average (TWA)
exposure and should be used
to assess personal exposures
during anesthetic
administration and in the
PACU. Where several
health-care workers perform
the same job, on the same
shift, and in the same work
area, and the length,
duration, and level of waste
gas exposures are similar,
an employer may sample a
representative fraction of
the employees instead of all
employees.
Area sampling is useful
for evaluating overall air
contaminant levels in a work
area and for investigating
cross-contamination with
other areas in the
health-care facility. Source
sampling can be used to
detect leaks in the
anesthesia delivery and
scavenging systems as well
as ineffective capture by
the scavenging system. Thus,
how samples are taken is a
critical point in any safety
program.
The OSHA Chemical
Information Manual contains
current sampling technology
for several of the
anesthetic gases that may be
present in anesthetizing
locations and PACUs.
