Packaging materials for EO gas ster iIizat ion
Frank €
104
Halleck, PAD
election of materials to package medical and hospital products for ethylene oxide (EO) gas sterilization should be based on specifications supplied by the materials manufacturer and experimentation with both the packaging materials and products to be packaged and sterilized. To assure sterility of a product within the processing time, the packaging material must allow uniform penetration of both the sterilant gas and moisture and allow release of gases after sterilization. Sterilant residuals remaining in products following sterilization can be deleterious to persons having direct contact with the products and also to the product. Hence, suitable methods must be employed to remove residuals and moisture. Selection of a proper packaging material cannot be made without considering thickness and method of sealing as well as evidence of sterility assurance gained by experimentation. TabIe 1 lists a number of available packaging materials-showing thickness and method of sealing-as well as summarizing advantages and disadvantages as related to EO gas sterilization programs. In hospitals, traditional wrapping materials for steam sterilization of medical supplies have been muslin and kraft paper. These same materials are used to package materials for EO gas sterilization. Although muslin and paper are satisfactory packaging materials for gas sterilization, they have two distinct disadvantages. Both materials are porous and highly absorbent, and their opacity does not allow visibility of the package contents. Because of these and other limitations, plastic films and pouches have been employed in hospital central service operations, in operating rooms and by manufacturers of sterile medical products. The following review of various materials that have been used as wrappings for EO gas sterilized packaged medical items discusses advantages and limitations of the materials and cautions against the use of unsatisfactory and untested pack-
AORN Journal, January 1975, Vol 21, N o 1
aging materials.
Textiles are traditional. Textile wraps have been traditional in hospital sterilization processes, and most early tests refer to no other type. Muslin is compatible with both steam and gas sterilization. With some limitations, it also can be employed to wrap items for dry heat sterilization. EO gas will penetrate muslin, assuring that articles so wrapped will be sterilized. A minimum of two layers of muslin (of 140 thread count) is recommended'j because its porosity allows penetration of the sterilant vapor and it is less susceptible to pin holes and tears. For prolonged (30 day) storage, two double layers are preferred for standard operating room packs. For periods in excess of 30 days, stored packs should be placed in hermetically sealed plastic wrappers. Muslin is probably the least expensive of hospital packaging materials
F'rank E Halleck, PhD, is director o f research, American Sterilizer Co, Eric, Pa. He hm a B A and M A front Wesleyan University, Middletown, Conn, and a PhD from Rutgers University, New Brunswick, NJ. This article is reprinted f r o m Packaging Digest, July 1974.
106
since it can be used repeatedly. Nevertheless, caution should be exercised, since frequently used and laundered fabrics may wear thin and not filter out airborne contamination. While muslin is rated high for mechanical strength, it is considered less effective than paper or plastic film as a long term, poststerilization contamination barrier. Microbial penetration of single and double muslinwrapped items was reporteds~*.20 after varied periods and conditions of storage. This was also found to be true in the author's laboratories. Microbial penetration took place through double-layered muslin; however, penetration took much longer in closed cabinets than in open storage, possibly because of reduced air currents in the cabinets. Four muslin layers, equivalent to two doubled layers, for hospital operating room packs retarded microbial penetration throughout 30 days of storage. Jean cloth and broadcloth (like muslin) are permeable to steam and gas, are good dust covers, weigh less, and may be more durable than muslin. Nonetheless, cautions similar to those mentioned for muslin must be observed if jean cloth or broadcloth are used in hospital sterilization operations. In Great Britain, a double layer of linen cloth was the common packaging material for hospital sterilization processes. However, use of this material now is limited because of its relatively high cost and high susceptibility to bacterial penetration.5 One of the most durable textiles, canvas, and similar tightly woven fabrics should not be used to wrap products for sterilization. Such materials cannot be relied upon to assure sterilization of the products they
AORN Journal, January 1975, Vol 21, N o 1
cover because the weave and additives retard passage of sterilant gases. Non-wovens, a new dimension. The newest dimension in sterile goods packaging material is the nonwoven textiles. These are produced with strands of plastic fibers randomly oriented to give the product strength and porosity; yet, the flexibility of woven textiles is retained. Nonwoven textiles currently on the US market include cellulose/nylon/ rayon combinations and a spunbonded olefin (polyethylene). The cellulose / nylon / rayon combination has been demonstrated to be an excellent b i ~ b a r r i e r ,but ~ current tests indicate that its use should be confined to steam sterilization.I8 Spunbonded olefin is highly permeable to EO and moisture, will serve as an extremely effective bacterial barrier, even under the stress of a vacuum,22 and has unusually high tear strength. Other favorable features of some nonwoven textiles include water repellency; resistance to rot, mildew, and molds; chemical inertness; and thermal stability. Greater use of nonwovens as packaging materials for medical supplies can be anticipated if costs are competitive with other acceptable packaging materials and if evidence is published to indicate that (shelf life) sterility maintenance quality is equally reliable or better. Paper used for years. Paper wrappers have been utilized by hospitals and medical product manufacturers for many years because they are readily penetrated by sterilant gases and withstand normal handling and storage. Special papers with specifications for porosity and formulated to meet very rigid quality requirements for uniformity are being used by
manufacturers of sterile medical products. Such papers include the generic types ranging from kraft to parchment and crepe. Many of these are suitable for EO gas or steam sterilization as permeability to sterilant gases has been demonstrated.15 In a recent evaluation,1° crepe and kraft paper met the requirements of acceptable packaging when considered in terms of sterilization rate, elution of gas residues (ie, EO gas and 2-chlorethanol) and shelf life sterility maintenance. Kraft and parchment paper also rated high for shelf life sterility maintenance.21 The 2-79 subcommittee of American National Standards Institute (ANSI) charged with establishing US standards for the aeration of products sterilized with EO gas, has rated paper wraps highly satisfactory for gas sterilization because of their rapid elution of sterilant residues." In Great Britain, detailed specifications for hospital paper wraps have been issued by the UK government, Department of Health & Social Security. Their major requirements are that the papers must be proved efficient barriers to airborne contamination, relatively inexpensive, and esthetically acceptable. Wrappers consisting of layers of the paper are recommended if the sterilized items are to be to red.^ In a biological indicator research study conducted by the author, glassine paper was tested for its permeability to EO gas and moisture because such envelopes are employed to enclose biological indicators used in both hospital and industrial sterility control procedures. The biological indicators, which consisted of paper strips impregnated
AORN Journal, January 1975, Vol 21, No 1
107
with a million spores, were enclosed in glassine packages and exposed to EO concentrations of 200 to 1,200 mg/liter. Tests show that 1) destruction of the Bacillus subtilis var globigii spores was a function of the concentration of the EO gas in the environment and 2) the glassine packaging allowed the penetration of the gas. Since paper products appear to be acceptable for packaging medical items that require gas sterilization, it is imperative to restate that only those papers which have been proven satisfactory by experimental evidence should be employed for hospital or industry practice. Detailed specifications and tight quality control standards, such as described by Cote,3must be adopted before employing a specific wrap in routine operations. As far as hospital procedures are concerned, the reuse of paper wrappers can be unsafeIs since this may compromise the sound principles of aseptic technique. PE film studies. Certain polyethylene (PE) films meet many of the requirements for an ideal medical product packaging material with the added advantage of transparency. Many studies6J2 have demonstrated the ease by which EO and moisture penetrate various PE films. While PE films can be manufactured from three basic types of resins, low, medium or high density, low density films are preferred for EO sterilization as they are highly permeable to the sterilant and easily elute sterilant residues.2 Experiments to demonstrate the difference in permeability of EO gas through low density polyethylene (LDPE) films of varied thicknesses were conducted by the author. Meas-
108
urement of permeability was based upon the time required to reduce a million Bacillus subtilis var globigii spores on a paper strip by 90%, which is called the “D” value by sterilization scientists. Data shown in Table 2 correlate spore destruction with thickness of the packaging film, and more importantly with concentration of the EO sterilant gas. With gas concentrations of 200 mg/liter, 38% more time was required for gas diffusion through a 6 mil film than through a 2 mil film to destroy 90% of the spore population. Increasing the sterilant gas concentration to above 600 mg/liter significantly reduced spore destruction time to the point where the thickness of the packaging material had no apparent influence, except for 20 mil film which is impractical for routine use. Further evidence that PE film can be used as a primary packaging material for medical items will be found in Tables 3 and 4. When PE film of identical thickness was utilized a s the primary wrap in single or double layers, EO gas adequately penetrated the films and effected sterilization of the medical items contained therein. There are limitations when additional packaging materials are used and a mixture of items are contained within a given package. Tables 3 and 4 show examples of sterility failures that could occur if an inexperienced person made a judgment that no advance experimental testing was required based solely upon evidence in literature and technical bulletins. This lack of sterility in the mixed medical item packages points to the need of standardized packaging con-
AORN Journal, January 1975, Vol 21, N o 1
>23
>23
Jean cloth
Linen
tape heat heat heat
2.5
I
I 4
1-2
Parchment
LDPE f i l m
HDPE f i l m
PP f i l m
heat
heat heat tape, heat
I.o
1-2
1-3
1-2
1-3
Polyester
[Mylar) Polyvinyl chloride
Polyvinyl alcohol
Nylon (polyamide
Cellophane
heat
tape, adhesive
I .5-2.0
4
tape
I .3
Crepe
Glassine
tape, adhesive
I .5
4 m i l thick
2
m i l thick
not recommended
not recommended
not recommended
not recommended
not recommended
1-3
not recommended
4 layers
2
layers
layers
4
2-4
2
very transparent, good barrier
durable, chemically stable
transparent, moisture penetrates
transparent, good shrink film, good barrier
transparent, durable good barrier
transparent, excellent barrier
excellent barrier same as LDPE
transparent, durable
high wet strength, good barrier
transparent, excellent barrier
flexible, less noisy, rapid drying, good barrier
inexpensive, disposable, good barrier, rapid elution o f gases
2-4
impermeable, fragile, becomes brittle
low permeability
low permeability
low permeability, elutes EO slowly, plasticizers and additives present
difficult t o seal, poor permeability
difficult t o handle
EO permeates t o o slowly
does not tolerate high temperature
noisy, not t o o flexible, becomes b r i t t l e
very fragile
expensive, less durable than plastic o f muslin
not durable, inflexible, noisy
impervious
very durable
l o t recommended layers
high cost, laundry & storage problems, very poor barrier
wettable, thinning due t o laundering (more durable]
flexible, durable reusable
flexible, durable reusable
! layers, double thickness
tape
wettable, thinning due t o laundering
wettable, thinning due t o laundering
! layers, double thickness
flexible, durable reusable
! layers, double thickness
tape
tape
flexible, durable reusable
! layers, double thickness
tape
Kraft paper
Canvas
>23
23
lmls)
Thickness
Broadcloth
Muslin
Packaging material
TABLE I Packaging materials for medical and hospital productsa Sealing Compatibility with EO gas sterilization advantages method Recommendations disadvantaqes
recommended with limitations b recommended with limitationsb
heat heat
varies
varies
PE/Surlyn
Polyester/PE
-
recommended with limitations b
heat
varies
PE/kraft
heat
varies
(PE/nylon/PE)
1-2
Foi I not recommended
recommended
~~
durable
durable, excellent barrier
durable moisture resistant, excellent barrier
durable, excellent barrier
recommended with limitations b
not recommended
durable, excellent barrier
durable, excellent barrier
durable, excellent barrier
recommended with limitations b
This l i s t does not include a l l currently marketed packaging materials.
b Use of these materials i s dependent upon experimental data.
a
heat, tape
4-0
(Spun bonded olefin) tape
tape
8.5-9.5
(Cellulose/nylon/rayon)
Non wovens
heat
varies
(PE/PP/PE)
Coextrusions
durable, excellent barrier
recommended with limitations b
heat
varies
PE/PVC durable, excellent barrier
durable, excellent barrier
recommended with limitations b
heat
varies
PE/nylon
durable, excellent barrier
recommended with limitations b
heat
varies
PE/cellophane
laminates
highly impermeable
not as flexible as muslin
low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
Polyethylene thickness (mils)
Ethylene oxide
2
concentrations (ms/l)
5.2 3.7 3.4 2.2 I .5 I.5
200 400
600 800
I000 I200
4
4
0 values 4.7 4.5 3.5 2.2 2.0 I .9
20
(minutes)
7.2 4.9 3.8 2.3 2.2 2.2
13.10
TABLE 3 Sterility a as demonstrated b y biological indicatorsb of medical items packaged in a variety of materials and wrapped i n single and double lavers of I and 2 m i l thick Dolvethvlenec. ,
. .
Type o f wrapping material Outer wrap
No of Inner wrap
tests
Spore strip results No sterile/ No exposed
I mil PE single layer
double layer
cloth towel
I
paper muslin
3 I 2 I
cloth towel paper muslin I m i l .. .PE double laver
3/3 6/6
2/2 2/2
3
2/2 5/5
I
2/2
2 mil PE single layer
I mil
2 mil double layer
I mil 2 mil
cloth towel muslin PE single layer PE double layer cloth towel muslin PE double wrap
PE single layer double layer
9/9
12/12 3/3 8/9
4/4 24/27**
8/9
** **
5/8 9/ I4**
Exposure conditions: 700 m g / f ethylene oxide, 54.4C, 1.75
112
AORN Journal, January 1975, Vol 21, N o I
hr
TABLE 4 Sterilitya as demonstrated by biological indicatorsb of medical items packaged i n a variety of materials and wrapped in groups of 2 t o 4 in single and double layers o f I and 2 rnil thick PE. ,pore Strip
Outer Type
wrapper
Item 2
Item I
I
mil PE double layer
2 mil PE single layer
Item 3
Item 4
paper cloth towel
paper
paper
muslin paper cellophane muslin
2 mil PE 2 m i l PE
2 m i l PE 2 rnil PE
I mil PE
I m i l PE
paper muslin
cellophane cloth towel muslin paper I mil nylon
cardboard box
paper
Paper
muslin
2 mil PE
2 mil PE
paper paper
paper paper
cloth towel
a/a 4/7**
cloth towel I m i l PE
cloth towel
paper
a/a
I m i l PE
o/a**
2 m i l nylon
2 mil nylon
3 rnil PE 2 mil nylon
1 I mil PE muslin
2 rnil PE
double laye
results
40 sterile/ 40 exposed
paper paper
cloth towel cloth towel
2 rnil PE
of inner wrapping materials
muslin paper rnil PE m i l nylon
3 2 2 2 2 2
mil PE
paper
m i l PE
4 mil PE
mil PE
m i l PE muslin cloth towel 2 m i l PE
cardboard box 2 m i l PE muslin paper 2 mil PE
3 rnil PE
3 mil PE
2 m i l PE 3 mil PE
muslin
Pa Per muslin cellophane
muslin cellophane
muslin
4 m i l nylon 4 mil PE
PE PE I m i l PE 2 m i l PE
2
mil 2 mil
cardboard box 2 mil PE
2 mil PE paper
4 mil PE
10/10
5/5 13/13
7/7 4/b** 4/b
paper
1 mil PE I mil PE
I mil PE 2 m i l PE 2 m i l PE
paper cloth towel
Paper cloth towel
5/5 3/3 b/8** 3/3 4/7 1/7 a/a 7/7
3 m i l PE
10/10
b/b
I
a
b
Exposure conditions: 700 m g / l ethylene oxide, 54.4"C,
1.75 hr. AMSCO
Medallion cycle@
Biological indicators AMSCO SpordexB spore strips Representative data of experimentation
**
Sterility not achieved
I I
AORN Journal, Januarg 1975, Vol 21, No 1
113
ditions in hospital and industrial operations where prior research. has demonstrated through repeated and reproducable experimentation that the sterilant gas and moisture will reach the item being sterilized and achieve adequate gas and moisture concentrations to result in sterility. Even with research data and standardized packaging, it is imperative that each and every sterilization cycle contain biological indicators within the load to provide assurance that proper gas sterilization conditions have occurred. The US Pharmacopeia (Vol XVIII pp 832-833) also recommends this procedure and understandably so. This is because charts of temperature and time cannot be substituted for actual laboratory demonstration of spore kill as evidence of product sterility. PP film is consideration. Polypropylene (PP) films have been recommended as primary packaging materials for medical items being sterilized.2 These films have many of the attributes of PE films. Reduced flexibility and higher heat sealing temperatures require special attention if PP films are employed in the routine packaging of medical items in hospital or industrial operations. Some PP films offer the dual advantage of being suitable for both ethylene oxide and steam steri1izati0n.I~ However, one may not indiscriminately avail himself of this advantage because the packaged items themselves may not withstand steam sterilization without damage. Other literat~re”.’~ and the results of a study by the author demonstrate that EO and moisture can penetrate PP films to allow sterility of the enclosed items. Nonetheless, caution
114
should prevail since data such as this are no guarantee that articles packaged in PP films will be sterile after gas sterilization. It is incumbent upon hospitals and industrial firms to collect research data that will assure themselves that gas sterilization processes employing PP film do indeed result in sterility of the wrapped products and that standardized operations continuously employ sterility monitoring with biological indicators. PVC blood bags. For over a decade, bags made of polyvinyl chloride (PVC) films have been used for acid citrate dextrose (ACD) solutions, and for the collection, storage, and administration of blood and blood products. PVC films are permeable to ethylene oxide and moisture and 1 to 3 mil films are recommended for packaging medical items.23 However, in contrast to the plastic films previously discussed, PVC films contain additives to the base polymer, polyvinyl chloride, to provide stability and flexibility. Additives such as stabilizers, ultraviolet absorbers, and plasticizers affect the transmission rates of EO gas and moisture.2 Hospitals and industrial firms employing these films (as packaging materials) should be aware of their formulations. Users should confirm efficacy of the films by either their own laboratory testing or by reports from recognized outside laboratories. Such tests or reports should provide assurance that 1) the films will allow sterilization of medical items and 2) the plastic additives and gas sterilization residuals will not leech out and compromise safety of the packaged items. The 2-79 sub-committee of
AORN Journal, January 1975, Vol 21, No 1
Routine use must also take into account proper selection of the EO gas sterilization cycle, the killing of gas resistant spores (biologicaI indicators), and the achievement of sterility of the wrapped medical items. Monitoring each sterilizer load with biological indicators is the only assurance that all sterilization conditions have been met t o achieve sterility of the wrapped products. Notes I. V G Alder, F I Alder, "Preservinq the sterili t y of surgical dressings wrapped in paper and other materials," Journal of Clinical Pathology, 14
( I96 I ) 76-79. 2. J Autian, "Drug packaging in plastics," Drug
I02 (1968) 54-62. 3. H Cote, Das Papier, 19 (1965) 364-351. 4. R B Davis, D T Maunder, "New system for
and Cosmetic industry,
aseptic
pouch packing,"
Modern Packaging, 40
(1967) 157-163. 5. Department of Health & Social Security, Department of heatlh and social security, Specification for paper sterilization plain (London, Eng,
1969). 6. M Dick, C E Feazel, "Resistance of plastics t o ethylene oxide," Modern Plastics, 38 (1960) 148-150. 7. P Dineen, "A comparison o f the resistance t o microbial penetration of muslin, paper and a nonwoven used as CSR wrappers," Laboratory Report, Capehart Hospital Supply Co, Loose-leaf pub, np.
8. E
D
Dyer, e t al, "Bacteriology study of muslin and parchment wrapped sterile supplies," Nursing Research, 15 (1966) 79-80.
9. R Ernst, "Ethylene oxide sterilization." vironmenf Newsletter, Looseleaf pub, np.
fn-
10. W L Guess, "Effects of packaging materials on ethylene oxide sterilization," Bulletin of Paramedic Drug Association,
Looseleaf pub, np. 18. Private Communication
Ferry,
NJ:
Cornell H o t e l and Administration Quarterly, May
1964.
F
20. P G Standard, D C Machel, G "Microbial
penetration
of
muslin
Mallison,
and
paper
wrapped sterile packs stored in open shelves and in closed cabinets," A p p l i e d Microbiology, 22
(1971) 432-437. 21. P G Standard, G F Mallison, C D Machel. "Microbial
penetration
through
three
double wrappers for sterile packs,''
types
20 (1973).
gases, vapors and liquids,"
26 ( 1973) 59-62. 22. A M Tracey, "New packaging for dispos-
ables,
reusable
Topics, 5 1
items
in
hospitals,"
Hospifal
(1973)72-74.
23. R Waach, et al, "Permeability of polymer l n d €ng Chem 47 (1955) 2524-2527.
films t o gases and vapors,"
Congress deudline dufes Feb 10-Postmark
deadline for forms
listing delegates and alternates Feb 15-Postmark
deadline for Con-
gress advance registrations Feb PO-Written change of delegate status to be received at Headquarters Mar 7-Letters
mailed from
Head-
quarters to delegates and alternates outlining duties
Modern Plasfics,
of
A p p l i e d Mi-
crobiology,
12. A Labovitis, "Permeability of polymers to
43
[ 1966) 139-213. 13. E McCullock,
Disinfecfion and Sferilirafion (Philadelphia: Lea & Febiger, 1936).
14. J J Perkins, Principles and Methods of Ster(Springfield, Ill: Charles C Thomas, 1956). 15. J J Perkins, Principles and Methods of Ster-
ilization
118
(Little
Capehart Hospital Supply Co, 1973). 19. F Reiter. "Flexible films for packaging," The
20 (1973) 59-75.
I I. Hospital Research & Testing Institute, "EO sterilization can be safe and effective," Research News,
2 ed (Springfield, 111: Charles C Thomas, 1969). 16. K Porter, "EO: despite call for action, research goes on," Hospitals, 47 (1973) 117-119. 17. Portex Nylon Co, Laboratory Report (Hythe, Kent, Eng: Portex Laboratories Ltd, A u g 4, 1969) ilization,
AORN Journal, January 1975, Vol 21, N o 1
Frank €
104
Halleck, PAD
election of materials to package medical and hospital products for ethylene oxide (EO) gas sterilization should be based on specifications supplied by the materials manufacturer and experimentation with both the packaging materials and products to be packaged and sterilized. To assure sterility of a product within the processing time, the packaging material must allow uniform penetration of both the sterilant gas and moisture and allow release of gases after sterilization. Sterilant residuals remaining in products following sterilization can be deleterious to persons having direct contact with the products and also to the product. Hence, suitable methods must be employed to remove residuals and moisture. Selection of a proper packaging material cannot be made without considering thickness and method of sealing as well as evidence of sterility assurance gained by experimentation. TabIe 1 lists a number of available packaging materials-showing thickness and method of sealing-as well as summarizing advantages and disadvantages as related to EO gas sterilization programs. In hospitals, traditional wrapping materials for steam sterilization of medical supplies have been muslin and kraft paper. These same materials are used to package materials for EO gas sterilization. Although muslin and paper are satisfactory packaging materials for gas sterilization, they have two distinct disadvantages. Both materials are porous and highly absorbent, and their opacity does not allow visibility of the package contents. Because of these and other limitations, plastic films and pouches have been employed in hospital central service operations, in operating rooms and by manufacturers of sterile medical products. The following review of various materials that have been used as wrappings for EO gas sterilized packaged medical items discusses advantages and limitations of the materials and cautions against the use of unsatisfactory and untested pack-
AORN Journal, January 1975, Vol 21, N o 1
aging materials.
Textiles are traditional. Textile wraps have been traditional in hospital sterilization processes, and most early tests refer to no other type. Muslin is compatible with both steam and gas sterilization. With some limitations, it also can be employed to wrap items for dry heat sterilization. EO gas will penetrate muslin, assuring that articles so wrapped will be sterilized. A minimum of two layers of muslin (of 140 thread count) is recommended'j because its porosity allows penetration of the sterilant vapor and it is less susceptible to pin holes and tears. For prolonged (30 day) storage, two double layers are preferred for standard operating room packs. For periods in excess of 30 days, stored packs should be placed in hermetically sealed plastic wrappers. Muslin is probably the least expensive of hospital packaging materials
F'rank E Halleck, PhD, is director o f research, American Sterilizer Co, Eric, Pa. He hm a B A and M A front Wesleyan University, Middletown, Conn, and a PhD from Rutgers University, New Brunswick, NJ. This article is reprinted f r o m Packaging Digest, July 1974.
106
since it can be used repeatedly. Nevertheless, caution should be exercised, since frequently used and laundered fabrics may wear thin and not filter out airborne contamination. While muslin is rated high for mechanical strength, it is considered less effective than paper or plastic film as a long term, poststerilization contamination barrier. Microbial penetration of single and double muslinwrapped items was reporteds~*.20 after varied periods and conditions of storage. This was also found to be true in the author's laboratories. Microbial penetration took place through double-layered muslin; however, penetration took much longer in closed cabinets than in open storage, possibly because of reduced air currents in the cabinets. Four muslin layers, equivalent to two doubled layers, for hospital operating room packs retarded microbial penetration throughout 30 days of storage. Jean cloth and broadcloth (like muslin) are permeable to steam and gas, are good dust covers, weigh less, and may be more durable than muslin. Nonetheless, cautions similar to those mentioned for muslin must be observed if jean cloth or broadcloth are used in hospital sterilization operations. In Great Britain, a double layer of linen cloth was the common packaging material for hospital sterilization processes. However, use of this material now is limited because of its relatively high cost and high susceptibility to bacterial penetration.5 One of the most durable textiles, canvas, and similar tightly woven fabrics should not be used to wrap products for sterilization. Such materials cannot be relied upon to assure sterilization of the products they
AORN Journal, January 1975, Vol 21, N o 1
cover because the weave and additives retard passage of sterilant gases. Non-wovens, a new dimension. The newest dimension in sterile goods packaging material is the nonwoven textiles. These are produced with strands of plastic fibers randomly oriented to give the product strength and porosity; yet, the flexibility of woven textiles is retained. Nonwoven textiles currently on the US market include cellulose/nylon/ rayon combinations and a spunbonded olefin (polyethylene). The cellulose / nylon / rayon combination has been demonstrated to be an excellent b i ~ b a r r i e r ,but ~ current tests indicate that its use should be confined to steam sterilization.I8 Spunbonded olefin is highly permeable to EO and moisture, will serve as an extremely effective bacterial barrier, even under the stress of a vacuum,22 and has unusually high tear strength. Other favorable features of some nonwoven textiles include water repellency; resistance to rot, mildew, and molds; chemical inertness; and thermal stability. Greater use of nonwovens as packaging materials for medical supplies can be anticipated if costs are competitive with other acceptable packaging materials and if evidence is published to indicate that (shelf life) sterility maintenance quality is equally reliable or better. Paper used for years. Paper wrappers have been utilized by hospitals and medical product manufacturers for many years because they are readily penetrated by sterilant gases and withstand normal handling and storage. Special papers with specifications for porosity and formulated to meet very rigid quality requirements for uniformity are being used by
manufacturers of sterile medical products. Such papers include the generic types ranging from kraft to parchment and crepe. Many of these are suitable for EO gas or steam sterilization as permeability to sterilant gases has been demonstrated.15 In a recent evaluation,1° crepe and kraft paper met the requirements of acceptable packaging when considered in terms of sterilization rate, elution of gas residues (ie, EO gas and 2-chlorethanol) and shelf life sterility maintenance. Kraft and parchment paper also rated high for shelf life sterility maintenance.21 The 2-79 subcommittee of American National Standards Institute (ANSI) charged with establishing US standards for the aeration of products sterilized with EO gas, has rated paper wraps highly satisfactory for gas sterilization because of their rapid elution of sterilant residues." In Great Britain, detailed specifications for hospital paper wraps have been issued by the UK government, Department of Health & Social Security. Their major requirements are that the papers must be proved efficient barriers to airborne contamination, relatively inexpensive, and esthetically acceptable. Wrappers consisting of layers of the paper are recommended if the sterilized items are to be to red.^ In a biological indicator research study conducted by the author, glassine paper was tested for its permeability to EO gas and moisture because such envelopes are employed to enclose biological indicators used in both hospital and industrial sterility control procedures. The biological indicators, which consisted of paper strips impregnated
AORN Journal, January 1975, Vol 21, No 1
107
with a million spores, were enclosed in glassine packages and exposed to EO concentrations of 200 to 1,200 mg/liter. Tests show that 1) destruction of the Bacillus subtilis var globigii spores was a function of the concentration of the EO gas in the environment and 2) the glassine packaging allowed the penetration of the gas. Since paper products appear to be acceptable for packaging medical items that require gas sterilization, it is imperative to restate that only those papers which have been proven satisfactory by experimental evidence should be employed for hospital or industry practice. Detailed specifications and tight quality control standards, such as described by Cote,3must be adopted before employing a specific wrap in routine operations. As far as hospital procedures are concerned, the reuse of paper wrappers can be unsafeIs since this may compromise the sound principles of aseptic technique. PE film studies. Certain polyethylene (PE) films meet many of the requirements for an ideal medical product packaging material with the added advantage of transparency. Many studies6J2 have demonstrated the ease by which EO and moisture penetrate various PE films. While PE films can be manufactured from three basic types of resins, low, medium or high density, low density films are preferred for EO sterilization as they are highly permeable to the sterilant and easily elute sterilant residues.2 Experiments to demonstrate the difference in permeability of EO gas through low density polyethylene (LDPE) films of varied thicknesses were conducted by the author. Meas-
108
urement of permeability was based upon the time required to reduce a million Bacillus subtilis var globigii spores on a paper strip by 90%, which is called the “D” value by sterilization scientists. Data shown in Table 2 correlate spore destruction with thickness of the packaging film, and more importantly with concentration of the EO sterilant gas. With gas concentrations of 200 mg/liter, 38% more time was required for gas diffusion through a 6 mil film than through a 2 mil film to destroy 90% of the spore population. Increasing the sterilant gas concentration to above 600 mg/liter significantly reduced spore destruction time to the point where the thickness of the packaging material had no apparent influence, except for 20 mil film which is impractical for routine use. Further evidence that PE film can be used as a primary packaging material for medical items will be found in Tables 3 and 4. When PE film of identical thickness was utilized a s the primary wrap in single or double layers, EO gas adequately penetrated the films and effected sterilization of the medical items contained therein. There are limitations when additional packaging materials are used and a mixture of items are contained within a given package. Tables 3 and 4 show examples of sterility failures that could occur if an inexperienced person made a judgment that no advance experimental testing was required based solely upon evidence in literature and technical bulletins. This lack of sterility in the mixed medical item packages points to the need of standardized packaging con-
AORN Journal, January 1975, Vol 21, N o 1
>23
>23
Jean cloth
Linen
tape heat heat heat
2.5
I
I 4
1-2
Parchment
LDPE f i l m
HDPE f i l m
PP f i l m
heat
heat heat tape, heat
I.o
1-2
1-3
1-2
1-3
Polyester
[Mylar) Polyvinyl chloride
Polyvinyl alcohol
Nylon (polyamide
Cellophane
heat
tape, adhesive
I .5-2.0
4
tape
I .3
Crepe
Glassine
tape, adhesive
I .5
4 m i l thick
2
m i l thick
not recommended
not recommended
not recommended
not recommended
not recommended
1-3
not recommended
4 layers
2
layers
layers
4
2-4
2
very transparent, good barrier
durable, chemically stable
transparent, moisture penetrates
transparent, good shrink film, good barrier
transparent, durable good barrier
transparent, excellent barrier
excellent barrier same as LDPE
transparent, durable
high wet strength, good barrier
transparent, excellent barrier
flexible, less noisy, rapid drying, good barrier
inexpensive, disposable, good barrier, rapid elution o f gases
2-4
impermeable, fragile, becomes brittle
low permeability
low permeability
low permeability, elutes EO slowly, plasticizers and additives present
difficult t o seal, poor permeability
difficult t o handle
EO permeates t o o slowly
does not tolerate high temperature
noisy, not t o o flexible, becomes b r i t t l e
very fragile
expensive, less durable than plastic o f muslin
not durable, inflexible, noisy
impervious
very durable
l o t recommended layers
high cost, laundry & storage problems, very poor barrier
wettable, thinning due t o laundering (more durable]
flexible, durable reusable
flexible, durable reusable
! layers, double thickness
tape
wettable, thinning due t o laundering
wettable, thinning due t o laundering
! layers, double thickness
flexible, durable reusable
! layers, double thickness
tape
tape
flexible, durable reusable
! layers, double thickness
tape
Kraft paper
Canvas
>23
23
lmls)
Thickness
Broadcloth
Muslin
Packaging material
TABLE I Packaging materials for medical and hospital productsa Sealing Compatibility with EO gas sterilization advantages method Recommendations disadvantaqes
recommended with limitations b recommended with limitationsb
heat heat
varies
varies
PE/Surlyn
Polyester/PE
-
recommended with limitations b
heat
varies
PE/kraft
heat
varies
(PE/nylon/PE)
1-2
Foi I not recommended
recommended
~~
durable
durable, excellent barrier
durable moisture resistant, excellent barrier
durable, excellent barrier
recommended with limitations b
not recommended
durable, excellent barrier
durable, excellent barrier
durable, excellent barrier
recommended with limitations b
This l i s t does not include a l l currently marketed packaging materials.
b Use of these materials i s dependent upon experimental data.
a
heat, tape
4-0
(Spun bonded olefin) tape
tape
8.5-9.5
(Cellulose/nylon/rayon)
Non wovens
heat
varies
(PE/PP/PE)
Coextrusions
durable, excellent barrier
recommended with limitations b
heat
varies
PE/PVC durable, excellent barrier
durable, excellent barrier
recommended with limitations b
heat
varies
PE/nylon
durable, excellent barrier
recommended with limitations b
heat
varies
PE/cellophane
laminates
highly impermeable
not as flexible as muslin
low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
may have low permeability
Polyethylene thickness (mils)
Ethylene oxide
2
concentrations (ms/l)
5.2 3.7 3.4 2.2 I .5 I.5
200 400
600 800
I000 I200
4
4
0 values 4.7 4.5 3.5 2.2 2.0 I .9
20
(minutes)
7.2 4.9 3.8 2.3 2.2 2.2
13.10
TABLE 3 Sterility a as demonstrated b y biological indicatorsb of medical items packaged in a variety of materials and wrapped i n single and double lavers of I and 2 m i l thick Dolvethvlenec. ,
. .
Type o f wrapping material Outer wrap
No of Inner wrap
tests
Spore strip results No sterile/ No exposed
I mil PE single layer
double layer
cloth towel
I
paper muslin
3 I 2 I
cloth towel paper muslin I m i l .. .PE double laver
3/3 6/6
2/2 2/2
3
2/2 5/5
I
2/2
2 mil PE single layer
I mil
2 mil double layer
I mil 2 mil
cloth towel muslin PE single layer PE double layer cloth towel muslin PE double wrap
PE single layer double layer
9/9
12/12 3/3 8/9
4/4 24/27**
8/9
** **
5/8 9/ I4**
Exposure conditions: 700 m g / f ethylene oxide, 54.4C, 1.75
112
AORN Journal, January 1975, Vol 21, N o I
hr
TABLE 4 Sterilitya as demonstrated by biological indicatorsb of medical items packaged i n a variety of materials and wrapped in groups of 2 t o 4 in single and double layers o f I and 2 rnil thick PE. ,pore Strip
Outer Type
wrapper
Item 2
Item I
I
mil PE double layer
2 mil PE single layer
Item 3
Item 4
paper cloth towel
paper
paper
muslin paper cellophane muslin
2 mil PE 2 m i l PE
2 m i l PE 2 rnil PE
I mil PE
I m i l PE
paper muslin
cellophane cloth towel muslin paper I mil nylon
cardboard box
paper
Paper
muslin
2 mil PE
2 mil PE
paper paper
paper paper
cloth towel
a/a 4/7**
cloth towel I m i l PE
cloth towel
paper
a/a
I m i l PE
o/a**
2 m i l nylon
2 mil nylon
3 rnil PE 2 mil nylon
1 I mil PE muslin
2 rnil PE
double laye
results
40 sterile/ 40 exposed
paper paper
cloth towel cloth towel
2 rnil PE
of inner wrapping materials
muslin paper rnil PE m i l nylon
3 2 2 2 2 2
mil PE
paper
m i l PE
4 mil PE
mil PE
m i l PE muslin cloth towel 2 m i l PE
cardboard box 2 m i l PE muslin paper 2 mil PE
3 rnil PE
3 mil PE
2 m i l PE 3 mil PE
muslin
Pa Per muslin cellophane
muslin cellophane
muslin
4 m i l nylon 4 mil PE
PE PE I m i l PE 2 m i l PE
2
mil 2 mil
cardboard box 2 mil PE
2 mil PE paper
4 mil PE
10/10
5/5 13/13
7/7 4/b** 4/b
paper
1 mil PE I mil PE
I mil PE 2 m i l PE 2 m i l PE
paper cloth towel
Paper cloth towel
5/5 3/3 b/8** 3/3 4/7 1/7 a/a 7/7
3 m i l PE
10/10
b/b
I
a
b
Exposure conditions: 700 m g / l ethylene oxide, 54.4"C,
1.75 hr. AMSCO
Medallion cycle@
Biological indicators AMSCO SpordexB spore strips Representative data of experimentation
**
Sterility not achieved
I I
AORN Journal, Januarg 1975, Vol 21, No 1
113
ditions in hospital and industrial operations where prior research. has demonstrated through repeated and reproducable experimentation that the sterilant gas and moisture will reach the item being sterilized and achieve adequate gas and moisture concentrations to result in sterility. Even with research data and standardized packaging, it is imperative that each and every sterilization cycle contain biological indicators within the load to provide assurance that proper gas sterilization conditions have occurred. The US Pharmacopeia (Vol XVIII pp 832-833) also recommends this procedure and understandably so. This is because charts of temperature and time cannot be substituted for actual laboratory demonstration of spore kill as evidence of product sterility. PP film is consideration. Polypropylene (PP) films have been recommended as primary packaging materials for medical items being sterilized.2 These films have many of the attributes of PE films. Reduced flexibility and higher heat sealing temperatures require special attention if PP films are employed in the routine packaging of medical items in hospital or industrial operations. Some PP films offer the dual advantage of being suitable for both ethylene oxide and steam steri1izati0n.I~ However, one may not indiscriminately avail himself of this advantage because the packaged items themselves may not withstand steam sterilization without damage. Other literat~re”.’~ and the results of a study by the author demonstrate that EO and moisture can penetrate PP films to allow sterility of the enclosed items. Nonetheless, caution
114
should prevail since data such as this are no guarantee that articles packaged in PP films will be sterile after gas sterilization. It is incumbent upon hospitals and industrial firms to collect research data that will assure themselves that gas sterilization processes employing PP film do indeed result in sterility of the wrapped products and that standardized operations continuously employ sterility monitoring with biological indicators. PVC blood bags. For over a decade, bags made of polyvinyl chloride (PVC) films have been used for acid citrate dextrose (ACD) solutions, and for the collection, storage, and administration of blood and blood products. PVC films are permeable to ethylene oxide and moisture and 1 to 3 mil films are recommended for packaging medical items.23 However, in contrast to the plastic films previously discussed, PVC films contain additives to the base polymer, polyvinyl chloride, to provide stability and flexibility. Additives such as stabilizers, ultraviolet absorbers, and plasticizers affect the transmission rates of EO gas and moisture.2 Hospitals and industrial firms employing these films (as packaging materials) should be aware of their formulations. Users should confirm efficacy of the films by either their own laboratory testing or by reports from recognized outside laboratories. Such tests or reports should provide assurance that 1) the films will allow sterilization of medical items and 2) the plastic additives and gas sterilization residuals will not leech out and compromise safety of the packaged items. The 2-79 sub-committee of
AORN Journal, January 1975, Vol 21, No 1
Routine use must also take into account proper selection of the EO gas sterilization cycle, the killing of gas resistant spores (biologicaI indicators), and the achievement of sterility of the wrapped medical items. Monitoring each sterilizer load with biological indicators is the only assurance that all sterilization conditions have been met t o achieve sterility of the wrapped products. Notes I. V G Alder, F I Alder, "Preservinq the sterili t y of surgical dressings wrapped in paper and other materials," Journal of Clinical Pathology, 14
( I96 I ) 76-79. 2. J Autian, "Drug packaging in plastics," Drug
I02 (1968) 54-62. 3. H Cote, Das Papier, 19 (1965) 364-351. 4. R B Davis, D T Maunder, "New system for
and Cosmetic industry,
aseptic
pouch packing,"
Modern Packaging, 40
(1967) 157-163. 5. Department of Health & Social Security, Department of heatlh and social security, Specification for paper sterilization plain (London, Eng,
1969). 6. M Dick, C E Feazel, "Resistance of plastics t o ethylene oxide," Modern Plastics, 38 (1960) 148-150. 7. P Dineen, "A comparison o f the resistance t o microbial penetration of muslin, paper and a nonwoven used as CSR wrappers," Laboratory Report, Capehart Hospital Supply Co, Loose-leaf pub, np.
8. E
D
Dyer, e t al, "Bacteriology study of muslin and parchment wrapped sterile supplies," Nursing Research, 15 (1966) 79-80.
9. R Ernst, "Ethylene oxide sterilization." vironmenf Newsletter, Looseleaf pub, np.
fn-
10. W L Guess, "Effects of packaging materials on ethylene oxide sterilization," Bulletin of Paramedic Drug Association,
Looseleaf pub, np. 18. Private Communication
Ferry,
NJ:
Cornell H o t e l and Administration Quarterly, May
1964.
F
20. P G Standard, D C Machel, G "Microbial
penetration
of
muslin
Mallison,
and
paper
wrapped sterile packs stored in open shelves and in closed cabinets," A p p l i e d Microbiology, 22
(1971) 432-437. 21. P G Standard, G F Mallison, C D Machel. "Microbial
penetration
through
three
double wrappers for sterile packs,''
types
20 (1973).
gases, vapors and liquids,"
26 ( 1973) 59-62. 22. A M Tracey, "New packaging for dispos-
ables,
reusable
Topics, 5 1
items
in
hospitals,"
Hospifal
(1973)72-74.
23. R Waach, et al, "Permeability of polymer l n d €ng Chem 47 (1955) 2524-2527.
films t o gases and vapors,"
Congress deudline dufes Feb 10-Postmark
deadline for forms
listing delegates and alternates Feb 15-Postmark
deadline for Con-
gress advance registrations Feb PO-Written change of delegate status to be received at Headquarters Mar 7-Letters
mailed from
Head-
quarters to delegates and alternates outlining duties
Modern Plasfics,
of
A p p l i e d Mi-
crobiology,
12. A Labovitis, "Permeability of polymers to
43
[ 1966) 139-213. 13. E McCullock,
Disinfecfion and Sferilirafion (Philadelphia: Lea & Febiger, 1936).
14. J J Perkins, Principles and Methods of Ster(Springfield, Ill: Charles C Thomas, 1956). 15. J J Perkins, Principles and Methods of Ster-
ilization
118
(Little
Capehart Hospital Supply Co, 1973). 19. F Reiter. "Flexible films for packaging," The
20 (1973) 59-75.
I I. Hospital Research & Testing Institute, "EO sterilization can be safe and effective," Research News,
2 ed (Springfield, 111: Charles C Thomas, 1969). 16. K Porter, "EO: despite call for action, research goes on," Hospitals, 47 (1973) 117-119. 17. Portex Nylon Co, Laboratory Report (Hythe, Kent, Eng: Portex Laboratories Ltd, A u g 4, 1969) ilization,
AORN Journal, January 1975, Vol 21, N o 1
