Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
Field of the Invention
~his invention relates to the disinfection of medical
apparatus; more particularly to the disinfection of heat-
and liquid-sensitive medical apparatus by the use of iso-
propanol in the vapor phase.
Description of the Prior Art
Conventional hospital sterilization practices call for
the use of steam or ethylene oxide gas. There are limitations,
however, on the types of equipment that may be subjected to
these sterilants. Steam may cause damage to heat-sensitive
materials such as plastics, rubber and the like. Ethylene
oxide gas sterilization, while carried out at lower temperature s
than steam sterilization, generally requires a relatively
long aeration period or "turn-around time". Certain types
of medical apparatus, especially expensive items, cannot be
out of service for that period of time. As to this latter
apparatus, when steam sterilization is also prohibited
because of material limitations, the hospital generally
resorts to the manual application of liquid disinfectants.
Even this procedure has serious drawbacks, however, because
parts of an instrument being disinfected in such manner may
be subject to chemical attack and/or other degradation by
the li~uid disinfectant, especially when immersion is used
as thc app ication technique.
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Specific types of medical apparatus that are not subject
to steam and/or ethylene oxide gas sterilization for the
reasons mentioned above include endoscopes, respiratory
therapy equipment and anesthesia equipment, wrapped or
unwrapped.
Endoscopes are instruments for the visual examination
of body cavities, such as bronchoscopes, laparoscopes,
arthoscopes, and upper and lower GI endoscopes. Fiberscopes
or flexible fiberoptic endoscopes are those endoscopes
having fiberoptic lighting; these are particularly adapted
to bending and generally provide a brighter light than
standard endoscopes. Endoscopic accessory or related
equipment includes cytology brushes and biopsy forceps used
in gastrointestinal endoscopy. The need for efficient and
effective disinfection and cleaning of endoscopic equipment
has been highlighted due to infections related to use of
this ~ind of equipment in hospitals. Nosocomial (hospital-
acquired) infections have been specifically associated with
inadequately cleaned respiratory equipment.
~he Ad Hoc Committee of Infection Control in the
Handling of Endoscopic Equipment, coordinated by the
Association for Practitioners in Infection Control (APIC),
in January 1978 established the following guidelines for the
cleaning and disinfection of flexible fiberoptic endoscopes
used in gastrointestinal endoscopy:
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"l. Scrupulous mechanical cieaning of insertion
tube and channels, using a detergent, is
imperative. This must be done immediately
after use to prevent the drying of secretions.
2. Inspection of equipment for damage.
3. Disinfection of endoscopic insertion tube and
all channels, performed with a chemical
substance having disinfecting action sufficient
to ki~ll all microorganisms (gram-positive
and gram negati~e bacteria, fungi mycobacteria,
and lipoph~ c and hydrophilic viruses~ except
bacteri~al spores when used according to manu-
factu~er's instructions.
4. ~de~uate rin$ing must follow such disinfection.
~t sh~uld be emphas~zed that adequate rinsing is
necessar~ to prevent possible residual toxic
e~fects of the disinfectant chemical and/or
aetergent. The r;~sks of toxicity with regard
to parti~cular disinfectants and/or detergents
need further exploration.
5. The inserti`on tube and inner channels should be
t~x~ughly and immediately air dried after
cleani`ng and prior to storage. (Bacteria will
mult~ply i'n a moist environment2.
6. Instruments to be stored.
7. Ethylene oxide sterilization is not generally
p~acti`cal. If used, it is imperative that
met~culous cleaning be accomplished as
described in ~uideline 1, and that it be fol-
lowed by adequate aeration.
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8. Because of the spring-like structural config-
uration, accessories such as biopsy forceps and
cytology brushes have been shown to be
extremely difficult to clean and disinfect.
After immediate surface cleaning with a deter-
gent/disinfectant, and rinsing, it is advisable
to use either steam under pressure or gas
Cethylene ox;de sterilization) or any other
treatment wh~ch has the capability of penetrating
the spring-like structures.
It IS emphasized that the heat treatments des-
cribed be applied only to accessories such as
~opsy- forceps, not to fiberoptic devices.
Improved structural configurations of the
accessor~es and~or more efficient cleaning
methods- need further exploration."
These guideli~nes illustrate some of the special con-
s~dexations and pro~lems ~n disinfecting flexible fiberoptic
endoscopes (fiberscopes~. Liquid disinfectants, detergents,
di~stilled water, steam and ethylene oxide gas (when pos-
siblel, haye thus been used in ~arying combinations to
acco~plis~ dis;nfection of this type of equipment. Even when
d~si~nfecti~n has ~een adequate, time-consuming air drying is
xe~u;xed ~nd ~nstruments are not immediately available for
xe-use. Presently~, endoscopic equipment is either simply
cleaned before re-use or is disinfected by immersion in some
li~qu~d ~Qcl~dal agent. Simple cleaning is not an adequate
process t~ p~qtect against cross infection. While dis-
~n~ectin~ by immexs~on in a liquid agent can be effective,
~i~t does not permi~t packaging of the item to protect it from
xec~ntaminat~on, i`n handl;~ng, transit or storage. Further-
mo~e, rt o ten damages the device, and generally requires
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copious rinsing with sterile distilled water to remove the
residual agent before use. Additionally, immersion and
rinsing are at the discretion of the worker and are frequently
inadequate. Liqu~ds also exert a dissolving action on
certain polyvinyl chlorides, silicones, acrylics, resins,
lens cements and other materials of the endoscopes. De-
tergents:can ~e abrasi~e and corrosive. The cumulative
e.ffects dim~nis-h.the use-life of the equipment.
An ~ptimum cleaning and dis~nfection process for endo-
scopes, .i~clud~ng fi~eroptic endoscopes and related equip-
~ent, would thexefore incorporate the following features:
l. Operate at low temperatures
2. Operate at atmospheric pressure or below (vacuum)
3. Lea~e no resi`dual chemical
4. Provide moisture-free articles following disin-
~ect~Qn
5. ~equire no aexation time
6. ~royide adequate penetratior. of springs and
~ntersti`ces ~y disinfectant
7. PxoYide adequate bactericidal action.
One Qb~ect~ve of this i~nvention, therefore, is.to
proyi~e. a. ~u~ck, penetrating, low-temperature treatment of
arti`cles ~t atmospheric pressure or ~elow (yacuum) which
.: destroy$ ~i~nfect;~ous organ~sms, yields essentially moisture-
: 25 f~ee a~ti~les without aerat~on t;me, and leaves no residual
agent.
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Another objective is to provide an efficient and
uniform treatment for all endoscopic (including fiberoptic)
and accessory equ~pment, as well as for other articles which,
cannot because of their structure or the materials of which
they consist ~e sterilized ~y conventional methods, or
cannot be disinfected ~y immersion. ,
Nathan U. S. Patent No. 867, 831 discloses the use of
alcohol fumes- to sterilize beer vessels. The vapors con-
dense w~thin a pressurized cham~er during sterilization.
The condensate will also dissolve resins formed in the beer-
manufacturing process., These high pressure, moisture and
resi~n-diss~lvi~ng features, which are favorable to beer
yessels, would damage endoscopic equipment.
Gibson U. S. Patent No. 246,494 uses alcohol vapors and
steam to restQre feathers. This ~s also a high temperature,
pressure process contraindicated for endoscopes.
~artner U. S. Patent No. ~03,853 teaçhes the use of a
methyl alcoh41 ~n approximately 55% concentration or ethyl
, alc~h~l and ~ater vapor in large quantities. The sterili-
zat,i~o,n cycle comprises essentially the following steps: (1)
exhausti~on of a steril~zation chamber to a pressure-gauge
yacuum of 7QQ mm; (,2~ introducing a mixture of water and
methy1 a,lc~hol ,i~to the chamber and vaporizing the same;
(31 a timed exposure (e.g., about 20 minutes~ after vaporizatior
i`s co~pleted; (4) admission of air to atmospheric pressure;
~51 all valved access to the chamber is closed and temperature
is m,ai~ntai~ned constant for 1 1/2 hours from initiation of
treatment; and, finally (6) a half-hour sweep of a strong
cu~rent of air through the chamber. The articles are preferably
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subjected to pressure after completion of this complicated
cycle. The teaching emphasizes the importance of large
vapor quantity and exhausting the chamber of air to a high
degree before introducing the disinfectant in order to
accomplish disinfection. -Thus biocidal activity is de-
pendent on laxge quantities of alcohol and water vapors
operating under a high vacuum. At 55% concentration, vapor
biocidal activity without this extremely high exhaustion
would be inadequate for disinfection. The large vapor
quantities required would also penetrate and exert haxmful
dissolving action on synthetic endoscopic materials.
Thus the alcohols and methods of these patents are
unsuitable for disinfection of endoscopic equipment in
~.odern hospital practice.
SUMMP.RY OF THE INVENTION
A process that is suitable or the disinfection of such
heat-sensitive and liquid-sensitive hospital equipment has
now been found to comprise the topical employment of
vaporized isopropanol usually in admixture with water vapor
in preferably minor ~roportion. The term "heat-sensitive"
as used herein refers to materials or articles which cannot
be exposed to a temperature greater than 150F. (65.56C.).
"Liquid-sensitive" as used herein refers to those materials
or articles which are adversely affected by contact with
liquids. The process of the present invention may be
applied to any medical item or device that heretofore could
not be sterilized at all; items which could not be sterilized
routinely after each use; or those which need not be sterilized
but only disinfected.
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A process that is suitable for the disinfection of such
heat- and liquid-sensitive hospital equipment has now been
found to consist in the topical employment of vaporized
isopropanol usually in admixture with water vapor in pref-
erably minor proportion. While isopropanol has been known
as a strong liquid disinfectant, its solubility in water
permitting its easy dilution, its high molecular density in
liquid phase and its resultant propensity to attack components
of the aforesaid heat- and liquid-sensitive hospital equipment
such as endoscopes had limited its usefulness for such
disinfection. Thus, even though isopropanol in the liquid
phase is known as a disinfectant (see for example U.S.
Patents Nos. 2,832,664 and 3,992,147; ~or the liquid steril-
ization of surgical catgut and seed husks, it was found to
be incompatible with such sensitive articles of hospital
equipment as endoscopes. For example, when the synthetic
(i.e. plastic or elastomeric) materials of the endoscopic
instruments are placed in the high density liquid environment,
liquid isopropanol or other alcohol will be absorbed into
the plastic indefinitely until the plastic is saturated with
the liquid, resulting in damage to the material. The plastic
(synthetic resinl is dissolved by the action of the liquid
alcohol, and components and additives of the resin (silicone,
polyvinyl chlorides, resins, cements, acrylics, polycarbonates,
etc.) are leached into solution.
On the other hand, isopropanol vapor will not leach
these materials. The maximum e~fects would be swelling from
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absorption of the vapor with subsequent recovery when
removed from that environment.
The process of the invention comprises as a first step
generating isopropanol vapor from a solution of isopropanol
and water. Small volume percentages of butanol and morpholine
also may be added to the solution. ~he concentration of
isopropanol may range from 40 to 100% isopropanol, with an
optimum concentration of 70%. The vapor is generated at a
temperature in the range of 45C. to 65C., a preferred
temperature being about 55C., that is, sufficiently high to
produce a significant vapor pressure, but below boiling
point so that equili~rium is reached. The vapor is intro-
duced into a chamber in which the articles to be disinfected
are placed. The cycle may be run at atmospheric pressure or
a vacuum (from about 25 to 35 mm. mercury absolute) may be
drawn in the chamber prior to introduction of the vapor.
Articles are exposed to the isopropanol vapor until disin-
fection is achieved. This may be in 4 minutes, and does not
e~ceed two hours. At the end of the cycles, the vapor is
exhausted from the chamber. There is no need for aeration;
vaporization will flash off any condensed isopropanol.
There is generally no residual agent; if any possible agent
remains it would be negligible in amount or effect.
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DESCRIPTIO~ OF THE PREFERRED EMBODIMENTS
optimal conditions for isopropanol vapor phase disin-
fection are 70% by volume isopropanol and 30% by volume
water at 55C. The effective temperature range for the
process is based on a maximum temperature, about 65C.
(determined by the heat resistance of the article) and a
minimum temperature, about 45C., below which impractically
long exposure times are required. The temperature of 55C.
(131F.) was selected because vir'tually all synthetic
(plastic/elastomericl materials commonly used in endoscopic
equipment are stable and unaffected by that temperature~
The 70% by volume isopropanol/ 30% by volume water mixture
is selected because this is the mixture most readily avail-
able. Higher concentrations will follow chemical and
biocidal kinetics with a modest increase in activity u2 to
100% by volume isopropanol and a rapid decrease in activity
occurring at less than 40% by volume isopropanol in 60~ by
volume water. Small volume percentages of butanol (e.g., up
to about 6~) and/or morpholine (e.g., up to about 5%) when
added to the isopropanol/water mixture tend to increase the
biocidal activity of the vapor.
Example
Tests were conducted under the just-described conditions
by placing an amount of the isopropanol/water mixture in a
stexilization chamber substantially in excess of that
needed in order to ensure vapor phase saturation.
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The organisms used in the tests were Pseudomonas
aeruginosa and Staphlococcus aureus. Glass plates and
penicylinder carriers were innoculated from a broth culture
to a population of 108 organisms per carrier, which provided
a condition of high population of resistant organisms
protected by much organic debris. Penicylinder carriers
are standard challenge detectors, used in hospital steril-
ization "packs" (packages of wet or dry, hard or soft
goods or articles to be sterilized) to determine the
bacteria ~ill achieved in a cycle. Penicylinders are a
testing requirement to satisfy the EPA relative to the
effectiveness of a disinfecting agent.
Plate carriers were exposed in uncovered petri dishes.
Isopropanol vapor phase disinfection was then carried out in
an atmospheric cycle. The isopropanol-water mixture was
vaporized into a closed chamber, at atmospheric pressure,
for 16 minutes.
Other plate carriers of the same organism populations
were again exposed under the same conditions of temperature
and concentration. This time, the vapor phase disinfection
was run in a vacuum cycle for 16 minutes. A vacuum of
approximately 28 inches of mercury was drawn in the closed
chamber and then the isopropanol-water mixture was vaporized
into the chamber and pressure restored to atmospheric.
After exposure, each carrier was cultured separately to
determine if all the carrier organisms were killed. Table A
gives the results of these experiments as a function of
exposure time, and also indicates the comparative effective-
ness of the atmospheric pressure cycle and the vacuum
cycle.
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TABLE A
10ORGANISMS ON GLASS PLATE: .
55 C. 70% V~V ISOPr~oPANOL, 3096 V/V WATER
VACUUM CYCLE
Organisms Surviving
Time P. Aeruginosa S. Aureus
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8 Minutes .O TNTC*
16 Minutes 0 10
ATMOSPHERIC PRESSURE CYCLE
4 Minutes TNTC TNTC
16 Minutes O TNTC
* - Too numerous to count
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The results shown in Table A indicated that Pseudomonas
aeruginosa was the least resistant organism and it was
therefore dropped from further tests. In the subsequent
experiments reported below in Table B, only Staphlococcus aureu ,
was innoculated in a 108 population per penicylinder carrier,
this micro-organism being especially suitable for testing
inasmuch as it is the resistant pathogen commonly found to
be the causative factor in nosocomial infections. Again,
six carriers were exposed in an open petri dish and six were
exposed sealed in a "peel pouch". A 70~ by volume isopropanol
and 30% by volume water mixture was placed in the chamber in
an amount in excess of that calculated to ensure vapor phase
saturation. The mixture was vaporized in the chamber at a
temperature of 55 C. The experiment was run in a substantiall
atmospheric pressure cycle, and then duplicated in the
vacuum cycle. Table B shows the results, again as a
function of time, with a comparison of atmospheric pressure
and vacu~m cycles:
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TABLE B
: S. AUREUS, 108/CARRIER
55 C. 70% v/v ISOPROPANOL/30% v/v WATER
VACUUM CYCLE
Time Bare Pouch
_
16 Minutes 5 of 6 Positive Growth 6 of 6 Positive Growth
32 Minutes 2 of 6 Positive Growth 1 of 6 Positive Growth
32 Minutes All Negative Growth All Negative Growth
32 Minutes All Negative Growth All Negative Growth
64 Minutes All Negative Growth All Negative.Growth
64 Minutes All Negative Growth All Negative Growth
64 Minutes All Negative Growth All Negative Growth
70 Minutes All Negative Growth All Negative Growth
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ATMOSPHERIC PRESSURE CYCLE ,.
.
Time Bare Pouch
32 Minutes 5 of 6 Positive Growth 6 of 6 Positive Growth
64 Minutes 2 of 6 Positive Growth 3 of 6 Positive Growth
100 Minutes 1 of 6 Positive Growth All Negative Growth
10~ Minutes 3 of 6 Positive Growth 4 of 6 Positive Growth
128 Minutes 1 of 6 Positive Growth All Negative Growth
128 Minutes 6 of 6 Positive Growth 5 of 6 Positive Growth
128 Minutes 4 of 6 Positive Growth 5 of 6 Positive Growth
128 Minutes All Negative Growth All Negative Growth
160 Minutes All Negative Growth All Negative Growth
. 160 Minutes All Negative Growth All Negative Growth
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The above Tables thus indica~e that adequate disin-
fection with a bacteriological kill greater than 50% can be
obtained in from 64 to 100 minutes (1 to 2 hours); and
complete sterilization in from 128 to 160 minutes (2-3
hours). .
Utilizing the features of isopropanol vapor compatible
with heat and li~uid sensitive equipment such as endoscopes,
as discussed above, and the disinfection/sterilization data
of the test results, it is possible to achieve an effective
disinfection cycle for this type of equipment by the use of .
isopropanol and water in the vapor phase.
