Safely Using Anesthetic Gases By Vince McLeod, CIH & Glenn R. Ketcham, CIH November/December 2003
Meet the Safety Guys! Beginning in the January/February
2004 issue, Vince McLeod and Glenn Ketcham will contribute their expertise to
each issue of ALN. Their column "Safety Guys" will address questions and issues
regarding workplace safety, OSHA, and other topics of particular importance for
lab animal facilities. This column will be open to reader comments and
questions. You may contact the authors with questions or you can send email to
pgalvin@alnmag.com with "Safety Guys" in the subject line.
O
ften our research endeavors involve animal
surgeries. We encounter animals of all sizes, from mice to horses and everything
in between. Surgical anesthesia is carried out in everything from bench top
"knockout boxes" to elaborate operating rooms. Read on to learn the most
commonly used anesthetic agents, their health effects, signs and symptoms of
exposure, how to determine if your anesthesia operations present exposure
concerns and finally what to do to minimize or eliminate exposures.
Common Agents - Health Effects
and Exposure Signs and Symptoms
The main anesthetics in use currently are
nitrous oxide and the class of compounds known as halogenated volatile agents.
The focus of this article is the halogenated agents. These are isoflurane,
enflurane, desflurane, sevoflurane, and halothane.
Although OSHA has not established permissible exposure limits (PEL) for
anesthetic gases, other agencies and organizations have set recommended exposure
limits. ACGIH set Threshold Limit Values (TLV) of 75 parts per million (ppm) for
enflurane and 50 ppm for halothane as 8-hour time-weighted averages (TWA). In
the absence of a TLV, the National Institute for Occupational Health and Safety
(NIOSH) recommended exposure limit (REL) of 2 ppm as an upper limit or "ceiling"
value should be used.
The NIOSH recommendation is based upon studies where halogenated anesthetic
agents have been linked to reproductive effects in women and neurological
effects in exposed workers. These retrospective studies have shown statistically
significant occurrence of excess spontaneous abortions in exposed female workers
and spouses of exposed males.1 Other studies have connected exposure
to the halogenated agents to congenital abnormalities in children of female
workers and increased incidence of hepatic disease. Chronic low-level exposures
such as those encountered in operating rooms have been associated with decreases
in cognitive and motor skills as well as the ability to perform complex tasks.
Acute exposures can produce depression of the central nervous system (CNS)
functions, respiratory, and cardiovascular systems and seizures.2
Typically, the halogenated agents are clear, colorless, volatile,
nonflammable liquids with mild sweet or pleasant odors. However, the reported
odor threshold for halothane, for example, is 33 ppm, which is very close to the
TLV of 50ppm. Therefore, do not rely on the presence of odors for adequate
warning of potential exposures. The signs and symptoms of acute exposures are
redness and tearing of the eyes, dizziness, headache, fatigue, slurred speech,
and reduced respiratory rate. Chronic exposures may include jaundice and an
enlarged and tender liver in addition to the reproductive effects mentioned
above. Irregularities of menstrual periods and alcohol intolerance have also
been reported.
Do You Have a Problem? Testing
and Monitoring for Leaks and Exposures
Air monitoring is the primary tool used to
evaluate potential exposures in the workplace. OSHA recommends conducting air
sampling for anesthetic gases every six months to evaluate worker exposures and
to check the effectiveness of control measures.1 The three basic
types of sampling are personal, area, and source sampling. Personal samples are
collected using small, calibrated air pumps worn by the worker with appropriate
collection media placed near the worker's breathing zone. They give the best
approximation of a worker's exposure level since they represent the actual
airborne contaminant concentration during the sampling period. Personal air
monitoring is the ideal method for determining a worker's time-weighted average
(TWA) exposure and should be used to assess personal exposures during anesthetic
administration and during post-operative recovery. Where several workers perform
the same job, one may sample a representative fraction of the employees instead
of all employees. One approach often used is to sample a number of surgeries
with the highest likelihood of exposure (worst case scenarios). If overexposures
are not found during these operations, it is unlikely that they would be found
during other lower risk events.
Area sampling is useful for evaluating overall air contaminant levels in a
work area and for investigating cross-contamination with other areas in the
facility. Area sampling is performed using the same equipment and media as for
personal sampling. The difference is that it is placed at a specific station for
the sample duration. Area sampling for some contaminants can also be done using
data-logging instruments.
Source sampling is used to detect leaks in the anesthesia delivery and
scavenging systems as well as ineffective capture by the scavenging system. The
only way to do this is with real-time direct reading instruments. For the
halogenated anesthetic agents the instrument of choice is a portable infrared
spectrophotometer. Since instruments of this type provide continuous sampling
and instantaneous feedback, sources of anesthetic gas leakage and effectiveness
of control measures are immediately determined. Although these instruments are
very expensive they can be rented by the week or month from IH equipment
companies.
One effective sampling strategy is to use a progression of the various
monitoring methods. First, use a direct-reading instrument to find and correct
any leaks in anesthetic equipment. Then screen for the levels of contaminants at
the source, in the area and breathing zones while equipment is in use. Identify
any areas or workers with levels above the action level (usually REL or TLV) and
then conduct full shift personal or area monitoring in these suspect areas to
establish the time-weighted average (TWA).
Prevention is the Key
Prudence dictates minimizing exposures to
anesthetic agents. Peak exposures usually occur during induction and the
post-operative recovery phase. The first line of defense is proper ventilation.
Areas used for anesthesia should have separate ventilation systems with no
recirculation. The recommended amount of ventilation is six to ten room air
changes per hour. In addition, properly balance ventilation systems so
anesthesia areas are slightly negative, in terms of air pressure, to surrounding
areas. This prevents any contaminants from flowing or mixing into other nearby
areas.
The second key to preventing potential exposures is to set up and maintain
anesthetic equipment properly. Delivery systems should have some way to scavenge
waste anesthetic gases. This is usually done with either a vacuum or exhaust
system or a chemical absorption filter canister. The later is weighed and
replaced when expended. Regularly scheduled equipment maintenance is the last
step. Leak check and inspect your anesthesia equipment routinely. Pay careful
attention to connection points and any seals and o-rings. Don't forget to have
plenty of replacement parts on hand.
The final key to prevention is to use common sense and keep up with
improvements in equipment design. Perform surgeries using nose cups and in
exhaust hoods whenever possible. Train workers to take care and avoid patient
exhaled air at critical times such as induction and recovery. Rotate personnel
performing surgeries if possible to further reduce any exposures.
Summary
Use of anesthetic agents is serious business.
Following a few basic rules will allow you to work safely with anesthetics. Use
the keys to prevention discussed above. Train your employees on proper equipment
operation and maintenance and the hazards of working with these chemicals.
Knowledge of exposure signs and symptoms is vital. Finally, put a monitoring
strategy in place as a check to make sure everything is working smoothly.
2 Documentation of the Threshold Limit Values and Biological Exposure
Indices, Seventh Edition, 2002, American Conference of Governmental Industrial
Hygienists (ACGIH), Cincinnati, OH
