Patent Application
20150247281
This disclosure relates to reducing the incidence of water remaining on steam sterilized packages in a medical setting.
Items used in medical settings such as gowns, sheets, drapes, and instruments used during surgery or other aseptic procedures are used on a daily basis. If these items are not received from a manufacturer in a sterile state, it is necessary for the medical facility to sterilize them before use. If these items are not disposable and are used more than once, it's required that they be sterilized prior to reuse. In order to sterilize medical items, they are normally first packaged within a protective sheet material wrap and then subject to the steam sterilization procedure. Occasionally, packages emerge from the sterilization process with moisture visible on the wrap. If this occurs, the tray must be rejected.
It is also important to maintain the sterility of the items inside the sterilized, wrapped package until the package is opened. Therefore, a wrap must be able to resist the penetration of bacteria, and must act as a filter to particles that can carry bacteria. Bacterial filtration efficiency (BFE) is a measure of how easily bacteria can pass through the sheet material used to wrap the medical items. A higher BFE indicates that the wrapped, sterilized items should remain bacteria free for a longer period of time than similar sterilized items wrapped with a lower BFE wrap material.
Appropriate protective sheet material includes those as shown, for example, in U.S. Pat. No. 5,635,134 to Bourne, et al. which discloses a multi-ply sterilization wrap which is formed by joining one or more sheets of sterilization wrap (e.g., two separate sheets or one sheet folded over) together to form two similarly sized, superposed panels that allow convenient dual wrapping of an article. As another example, US patent publication 20010036519 by Robert T. Bayer discloses a two ply sterilization wrap that is formed of a single sheet of sterilization wrap material which is folded to form two similarly sized, superposed panels that are bonded to each other. As yet another example, US patent publication No. 20050163654 by Stecklein, et al. discloses a sterilization wrap material that has a first main panel and a second panel that is smaller than the main panel. The second panel is superposed and bonded to the central portion of the main panel such that it is contained entirely within the main panel to reinforce the main panel and/or provide additional absorbency. U.S. Pat. No. 8,261,963 to Gaynor et al., discloses a multi-panel sterilization assembly that includes a barrier panel composed of a permeable sheet material having barrier properties, panel attachment means for securing the barrier panel into a package; and a fold protection panel. The barrier panel includes: a first surface and a second opposing surface; a first end generally defining a pre-determined fold line; a second end opposite the first end; a first edge that is generally perpendicular to the pre-determined fold line; a second edge that is generally opposite the pre-determined fold line; and a third edge that is generally perpendicular to the pre-determined fold line. Sterilization wraps may also have a single ply only and these are suitable for use with this disclosure.
Sterilization wraps are commonly made from non-woven materials made by the spunbonding and meltblowing processes and are often electret treated to increase the bacterial filtration efficiency. Electret treatment is described, for example, in U.S. Pat. No. 5,592,357.
Items subjected to steam sterilization can sometimes emerge from the sterilization process still containing visible water. These water-containing steam sterilized packages are referred to as “wet packs” and require re-sterilization, costing the medical facility time and money. Reduction in wet packs while maintaining an acceptable BFE level is highly desirable.
The present disclosure describes a surfactant treatment for a polyolefinic nonwoven fabric used to wrap items to be sterilized. The surfactant treatment consists essentially of carbon, hydrogen and oxygen atoms. The surfactant treated sterile wrap has a BFE after electret treatment and after sterilization of at least 97 percent. This treatment should produce fewer wet packs than the same fabric after electret treatment and after sterilization but without such surfactant treatment.
This disclosure also describes a sterilization wrap that has the dried residue of an aqueously applied surfactant treatment. The surfactant treatment is essentially free of silicon, potassium, phosphorus and sulfur, and the sterilization wrap has a BFE after electret treatment and after sterilization of at least 97 percent.
Lastly, a method of reducing medical wet packs post sterilization is provided. This method has the steps of providing a nonwoven fabric, applying a surfactant treatment consisting essentially of carbon, hydrogen and oxygen atoms to the nonwoven fabric, drying the fabric, electret treating the fabric, wrapping items to be sterilized in the fabric and sterilizing the wrapped items.
It is to be understood that the following description is only exemplary of the principles of the present disclosure, and should not be viewed as narrowing the pending claims. Those skilled in the art will appreciate that aspects of the various embodiments discussed may be interchanged and modified without departing from the scope and spirit of the disclosure.
Medical trays containing surgical instruments are wrapped, generally with a nonwoven fabric wrap, and steam sterilized. If, after sterilization, any visible moisture is observed on the wrap or inside the tray, the tray must be rejected. Sterilized trays should be wrapped in materials having high bacterial filtration efficiency (BFE) so that they remain bacteria free until they are opened for use.
One exemplary sterilization wrap is a spunbond/meltblown/spunbond (SMS) material like that described in U.S. Pat. No. 8,261,963. The basis weight of such SMS material(s) may be from 1 ounce per square yard or “osy” (which is approximately 33 grams per square meter or “gsm”) to about 3 osy (100 gsm). For example, the basis weight of the SMS material(s) may be from 1.2 osy (40 gsm) to about 2 osy (67 gsm). As another example, the basis weight of the SMS material(s) may be from 1.4 osy (47 gsm) to about 1.8 osy (60 gsm). The basis weight may be determined in accordance with ASTM D3776-07. Multiple plies or layers of SMS material may be used to provide basis weights ranging from about 2 osy (67 gsm) to about 5 osy (167 gsm).
As used herein the term “nonwoven fabric or web” means a web having a structure of individual fibers or threads which are interlaid, but not in an identifiable manner as in a knitted fabric. Nonwoven fabrics or webs have been formed from many processes such as for example, meltblowing processes, spunbonding processes, and bonded carded web processes. The basis weight of nonwoven fabrics is usually expressed in ounces of material per square yard (osy) or grams per square meter (gsm) and the fiber diameters useful are usually expressed in microns. (Note that to convert from osy to gsm, multiply osy by 33.91).
As used herein the term “spunbonded fibers” refers to small diameter fibers which are formed by extruding molten thermoplastic material as filaments from a plurality of fine, usually circular capillaries of a spinneret with the diameter of the extruded filaments then being rapidly reduced as by, for example, in U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S. Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. 3,502,763 to Hartman, and U.S. Pat. No. 3,542,615 to Dobo et al. Spunbond fibers are generally not tacky when they are deposited onto a collecting sheet. Spunbond fibers are generally continuous and have average diameters (from a sample of at least 10) larger than 7 microns, more particularly, between about 10 and 20 microns. The fibers may also have shapes such as those described in U.S. Pat. No. 5,277,976 to Hogle et al., U.S. Pat. No. 5,466,410 to Hills and U.S. Pat. Nos. 5,069,970 and 5,057,368 to Largman et al., which describe fibers with unconventional shapes.
As used herein the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten threads or filaments into converging high velocity, usually hot, gas (e.g. air) streams which attenuate the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting sheet to form a web of randomly dispersed meltblown fibers. Such a process is disclosed, for example, in U.S. Pat. No. 3,849,241 to Butin et al. Meltblown fibers are microfibers which may be continuous or discontinuous, are generally smaller than 10 microns in average diameter, and are generally tacky when deposited onto a collecting sheet.
The permeability of the wrap material may range from 25 to about 500 cubic feet per minute (CFM) as characterized in terms of Frazier permeability. For example, the permeability of the wrap material may range from 50 to about 400 cubic feet per lo minute. As yet another example, the permeability of the wrap material may range from 100 to about 300 cubic feet per minute. The Frazier permeability, which expresses the permeability of a material in terms of cubic feet per minute of air through a square foot of area of a surface of the material at a pressure drop of 0.5 inch of water (or 125 Pa), was determined utilizing a Frazier Air Permeability Tester available from the Frazier Precision Instrument Company and measured in accordance with Federal Test Method 5450, Standard No. 191A. When the wrap material contains SMS material(s) having basis weights ranging from about 1 osy (33 gsm) to about 2.6 osy (87 gsm), the permeability of the wrap material may range from about 20 cubic feet per minute to about 75 cubic feet per minute when determined generally in accordance with ISO 9237:1995 (measured with an automated air permeability machine using a 38 cm2 head at a test pressure of 125 Pa,—exemplary air permeability machine is TEXTEST FX 3300 available from TEXTEST AG, Switzerland). If multiple plies or layers of SMS material are used to provide basis weights ranging from about 2 osy (67 gsm) to about 5 osy (167 gsm), the permeability of the wrap material may range from about 10 cubic feet per minute to about 30 cubic feet per minute when determined generally in accordance with ISO 9237:1995.
There are a number of methods of characterizing the air filtration efficiencies of nonwoven webs. One method uses a TSI, Inc. (St. Paul, Minn.) Model 8130 Automated Filter Tester (AFT). This test (the TSI test) is less expensive than the BFE test, and while less accurate, gives directional and relative indications of filtration efficiency. The Model 8110 AFT measures pressure drop and particle filtration characteristics for air filtration media. The AFT utilizes a compressed air nebulizer to generate a sub-micron aerosol of sodium chloride particles which serves as the challenge aerosol for measuring filter performance. The characteristic size of the particles used in these measurements was 0.1 micrometer. Typical air flow rates were between 31 liter per minute and 85 liters per minute. The AFT test was performed on a sample area of 140 square cm. The performance or efficiency of a filter medium is expressed as the percentage of sodium chloride particles which penetrate the filter. Penetration is defined as transmission of a particle through the filter medium. The transmitted particles were detected downstream from the filter. The percent penetration (% P) reflects the ratio of the downstream particle count to the upstream particle count. Light scattering was used for the detection and counting of the sodium chloride particles.
Bacterial filtration efficiency (BFE) employs a test where samples are challenged with a biological aerosol of Staphylococcus aureus and the results employ a ratio of the bacterial challenge counts to sample effluent counts, to determine percent bacterial filtration efficiency (% BFE). For the tests herein, a suspension of S. aureus was aerosolized using a nebulizer and delivered to the test article at a constant flow rate. The aerosol droplets were drawn through a six-stage, viable particle Andersen sampler for collection. This test procedure allows a reproducible bacterial challenge to be delivered to the sterilization wrap and complies with ATSM F2101 (Nelson Lab #373162). The testing herein was performed by Nelson Laboratories, Inc., Salt Lake City, Utah, according to “Bacterial Filtration Efficiency,” Procedure No. SOPARO007L.1. The acceptable BFE for a sterilization wrap is desirably at least 97 percent, more desirably 98 percent and still more desirably 99 percent or greater.
The Andersen sampler is known in the art and is used to collect viable samples of airborne bacteria and fungal spores. The samples can act as a measure of the number of bacteria or fungal spores in the air at a specific location and time. The sampler works through impaction in which air is drawn through a sampling head with 400 small holes at constant rate (in this case 28.3 L/min or 1 cubic foot per minute) for a known period of time. Before sampling a media plate is placed inside the sampling head and as air is pulled through the holes heavier particles such as bacteria and fungal spore's impact on the agar surface and stick there. The air continues through the sampler and into the pump. After sampling the plate can be removed for culturing.
It has been found that electret treatment increases the BFE of a fabric. Electret treatment is described, for example, in U.S. Pat. No. 5,592,357. Electret treatment is used to produce an intense corona current at reduced voltages to help reduce the potential for arcing and provide a more efficient, stable discharge at atmospheric pressure, for electrostatically charging an advancing web or film. Once ionization occurs, excess charged particles cannot be lost until they collide with a solid body, preferably the remaining electrode, achieving the desired result. It has been found that this applies to both AC and DC voltages.
Placement of a thin non-electron absorbing gas layer in the vicinity of an electrode is advantageously accomplished by various means. For example, the charging bar can be replaced with a longitudinally extending tube having spaced apertures for delivering a gas to the discharge-forming elements of the electrode. These discharge-forming elements can include either a series of pins which extend through the spaced apertures of the tube, or a series of nozzles which project from the surface of the tube. In either case, this places the gas in the vicinity of the pins, or the nozzles, which in turn receive appropriate biasing voltages for developing the electric field which is to produce the improved discharge. Alternatively, the charging shell can be replaced with a hollow body which similarly incorporates a series of apertures, and a cooperating series of pins or nozzles, to achieve a similar result.
Of all the methods available for sterilization, moist heat in the form of saturated steam under pressure is the most widely used and the most dependable. Steam sterilization is nontoxic, inexpensive, rapidly microbicidal, sporicidal, and rapidly heats and penetrates fabrics. The basic principle of steam sterilization, as accomplished in an autoclave, is to expose each item to direct steam contact at the required temperature and pressure for the specified time. Thus, there are four parameters of steam sterilization: steam, pressure, temperature, and time. The ideal steam for sterilization is dry saturated steam and entrained water (dryness fraction ≧97%). Pressure serves as a means to obtain the high temperatures necessary to quickly kill microorganisms. Specific temperatures must be obtained to ensure the microbicidal activity. The two common steam-sterilizing temperatures are 121° C. (250° F.) and 132° C. (270° F.). These temperatures (and other high temperatures) must be maintained for a minimal time to kill microorganisms. Recognized minimum exposure periods for sterilization of wrapped healthcare supplies are 30 minutes at 121° C. (250° F.) in a gravity displacement sterilizer or 4 minutes at 132° C. (270° F.) in a pre-vacuum sterilizer. Sterilization for the BFE tests herein took place at 134° C. (273° F.).
The criteria for deciding that a wet pack exists after sterilization is two-fold; firstly, is the tray's weight after (i.e. post) sterilization higher than the pre-sterilization weight by 3 percent or more? Secondly, is there any sign of moisture visible on the top of the tray or inside of the tray after sterilization? If the answer to either or both of these questions is “yes” then the tray is a wet pack.
Surfactant treatments for the nonwoven sterile wrap were investigated, in the belief that a more wettable wrap would result in fewer wet packs since the moisture would spread out on the wrap, thus covering more surface area and evaporating more easily and quickly. The wrap used in the testing was a 2.57 osy (87 gsm) SMS except for Sample 1 which was a 1.85 osy (62.7 gsm) SMS. The surfactant treatment was applied to the wrap by a dip and squeeze (saturation) process, using an aqueous formulation containing the surfactant. The amount of surfactant treatment in weight percent is indicated in the Sample descriptions below for the treated and dried wrap. The wrap having the dried surfactant treatment residue was subjected to electret treatment as indicated in the Table. The trays were wrapped using the double layer wrap and according to the method of U.S. Pat. No. 5,635,134, sterilized at 134° C. (273° F.) and tested for wet packs. TSI and BFE were tested according to the procedures above.
Samples with treatments that were tested include the following:
Electret conditions:
As can be seen from the results, the first four samples, containing elements other than simply carbon, hydrogen and oxygen, had a very small increase in TSI after electret treatment. This indicates that the BFE results would likely also be poor as shown by sample 2 and for this reason the more expensive BFE test was not run on the other samples with poor TSI results. Beginning with sample 5, however, the difference between the pre- and post-electret TSI was significant. The BFE data that was collected also showed good results, pre- and post-sterilization. The wet pack results were good, except for sample 8 which had a very high add on amount of the Pluronic® P123 treatment.
Electret treatment is used, as discussed above, to increase the BFE of a fabric. This treatment also increases the TSI. It is not believed that differing electret treatment conditions had a great effect on these result and is reported merely for thoroughness. The data shows that the treatments containing other than carbon, hydrogen and oxygen (C—H—O) atoms do not show an appreciable increase in TSI after electret treatment, indicating that they do not allow the fabric to hold a charge and are therefore unsuitable for electret charging. Samples 1, 2 and 4 have little or no positive change in TSI after electret treatment. Note that sample three does show an average increase in TSI but the range of results is extremely wide, leading to questions about repeatability and the value of such results. The successful candidates display large increases in TSI after electret treatment, showing that they allow the web to absorb the charge needed to increase the barrier to microbial infiltration.
Regardless of the mechanism of operation, it is clear that the treatments for Samples 5-9 that are surfactants containing only carbon, hydrogen and oxygen (C—H—O) atoms are superior to other treatments containing silicon, phosphorus, sulfur and the like, though amounts above 1.5 appear to be less promising. Treatments that are C—H—O surfactants that are essentially free of silicon, potassium, phosphorus and sulfur provide superior TSI NaCl filtration and reduced wet packs compared to the other treatments 1-4, except at very high treatment amounts. The preferred amount of surfactant add on is between a positive amount and 1 weight percent or at most
1.5%. Treatments limited to having only C—H—O surfactants also produce fewer wet packs when compared to the same base fabric without any treatment (i.e. Sample 10).
As used herein and in the claims, the term “comprising” is inclusive or open-ended and does not exclude additional unrecited elements, compositional components, or procedure steps.
While various patents have been incorporated herein by reference, to the extent there is any inconsistency between incorporated material and that of the written specification, the written specification shall control. In addition, while the disclosure has been described in detail with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various alterations, modifications and other changes may be made to the disclosure without departing from the spirit and scope of the present disclosure. It is therefore intended that the claims cover all such modifications, alterations and other changes encompassed by the appended claims.
