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Ethylene Oxide sterilization is a low
temperature
sterilization
process designed to sterilize instruments or devices that are
sensitive to heat and/or moisture. ETO is a colorless gas that is
flammable and explosive. The four essential
parameters
(operational ranges) are: gas concentration (450 to 1200 mg/l);
temperature (37 to 63°C); relative humidity (40 to 80%) (water
molecules carry ETO to reactive sites); and exposure time (1 to 6
hours). These influence the effectiveness of ETO sterilization.
Within certain limitations, an increase in gas concentration and
temperature may shorten the time necessary for achieving
sterilization.
The basic ETO sterilization cycle consists of five
stages (i.e., preconditioning and humidification, gas introduction,
exposure, evacuation, and air washes) and takes approximately 2-1/2
hrs excluding aeration time. Mechanical aeration for 8 to 12 hours
at 50 to 60°C allows desorption of the toxic ETO residual contained
in exposed absorbent materials. Most modern ETO sterilizers combine
sterilization and aeration in the same chamber as a continuous
process. These ETO models minimize potential ETO exposure during
door opening and load transfer to the aerator. Ambient room
aeration also will achieve desorption of the toxic ETO but requires
7 days at 20°C. There are no federal regulations for ETO sterilizer
emission; however, many states have promulgated emission-control
regulations.
Microbicidal Activity:
The excellent microbicidal activity of ETO has been
demonstrated in several studies and summarized in published
reports. ETO inactivates all microorganisms although bacterial
spores (especially
Bacillus
atrophaeus) are more resistant than other microorganisms.
For this reason B. atrophaeus is the recommended
biological indicator. Like
all sterilization processes, the effectiveness of ETO sterilization
can be altered by lumen length, lumen diameter, inorganic salts, and
organic materials. For example, although ETO is not used commonly
for reprocessing endoscopes, several studies have shown failure of
ETO in inactivating contaminating spores in endoscope channels or
lumen test units and residual ETO levels averaging 66.2 ppm even
after the standard degassing time. Failure of ETO also has been
observed when dental handpieces were contaminated with Streptococcus
mutans and exposed to ETO. It is recommended that dental handpieces
be steam sterilized.
Uses:
ETO is used in healthcare facilities to sterilize
critical items (and sometimes semi-critical items) that are moisture
or heat sensitive and cannot be sterilized by steam sterilization.
The use of ETO evolved when few alternatives existed for
sterilizing heat- and moisture-sensitive medical devices; however,
favorable properties account for its continued widespread use. Two
ETO gas mixtures are available to replace ETO-chlorofluorocarbon
(CFC) mixtures for large capacity, tank-supplied sterilizers. The
ETO-carbon dioxide (CO2) mixture consists of 8.5% ETO and 91.5%
CO2. This mixture is less expensive than ETO-hydro
chlorofluorocarbons (HCFC), but a disadvantage is the need for
pressure vessels rated for steam sterilization, because higher
pressures (28-psi gauge) are required. The other mixture, which is
a drop-in CFC replacement, is ETO mixed with HCFC.
Following the sterilization cycle:
ETO is absorbed by many materials. For this reason,
following sterilization the item must undergo aeration to remove
residual ETO. Guidelines have been promulgated regarding allowable
ETO limits for devices that depend on how the device is used, how
often, and how long in order to pose a minimal risk to patients in
normal product use.
Disadvantages / hazardous:
The main disadvantages associated with ETO are the
lengthy cycle time, the cost, and its potential hazards to patients
and staff; the main advantage is that it can sterilize heat- or
moisture-sensitive medical equipment without deleterious effects on
the material used in the medical devices. Acute exposure to ETO may
result in irritation (e.g., to skin, eyes, gastrointestinal or
respiratory tracts) and central nervous system depression. Chronic
inhalation has been linked to the formation of cataracts, cognitive
impairment, neurologic dysfunction, and disabling polyneuropathies.
Occupational exposure in healthcare facilities has been linked to
hematologic changes and an increased risk of spontaneous abortions
and various cancers. ETO should be considered a known human
carcinogen.
Damaging to ozone:
HCFCs are approximately 50-fold less damaging to the
earth’s ozone layer than are CFCs. The EPA will begin regulation of
HCFC in the year 2015 and will terminate production in the year
2030. Two companies provide ETO-HCFC mixtures as drop-in
replacement for CFC-12; one mixture consists of 8.6% ETO and 91.4%
HCFC, and the other mixture is composed of 10% ETO and 90% HCFC. An
alternative to the pressurized mixed gas ETO systems is 100% ETO.
The 100% ETO sterilizers using unit-dose cartridges eliminate the
need for external tanks.
ETO Exposure:
ETO toxicity has been established in a variety of
animals. Exposure to ETO can cause eye pain, sore throat,
difficulty breathing and blurred vision. Exposure can also cause
dizziness, nausea, headache, convulsions, blisters and vomiting and
coughing. In a variety of in vitro and animal studies, ETO has been
demonstrated to be carcinogenic. ETO has been linked to spontaneous
abortion, genetic damage, nerve damage, peripheral paralysis, muscle
weakness, and impaired thinking and memory. Occupational exposure
in healthcare facilities has been linked to an increased risk of
spontaneous abortions and various cancers. Injuries (e.g., tissue
burns) to patients have been associated with ETO residues in
implants used in surgical procedures. Residual ETO in capillary
flow dialysis membranes has been shown to be neurotoxic in vitro.
OSHA has established a PEL of 1 ppm airborne ETO in the workplace,
expressed as a TWA for an 8-hour work shift in a 40-hour work week.
The “action level” for ETO is 0.5 ppm, expressed as an 8-hour TWA,
and the short-term excursion limit is 5 ppm, expressed as a
15-minute TWA. Several personnel monitoring methods (e.g., charcoal
tubes and passive sampling devices) are in use. OSHA has
established a PEL of 5 ppm for ethylene chlorohydrin (a toxic
by-product of ETO) in the workplace. Additional information
regarding use of ETO in health care facilities is available from
NIOSH. See the complete recommendations
on sterilizer and disinfection at
www.cdc.gov
“Guideline for Disinfection and Sterilization in Healthcare
Facilities, 2008”.
ATS, Inc. provides
products
and
services to assist your
office in its endeavor for sterility assurance, protecting yourself,
your patients and staff from the spread of harmful communicable
diseases.
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