* Reviews the characteristics of the ideal sterilization wrap.
* Provides guidance to infection control and central processing professionals in choosing an appropriate wrap.
The use of sterile surgical instruments is a keystone of surgery. Guidelines from the Centers for Disease Control and Prevention recommend that all surgical instruments should be sterile.1 For more than 75 years, hospitals have been packaging surgical instruments to maintain sterility until instrument use. The sterilization wrap must provide protection against contact contamination during handling and must provide an effective barrier to microbial penetration.
Current Use of Sterilization Wraps
There are several choices in methods to maintain sterility of surgical instruments including rigid containers, peel pouches of plastic and/or paper, and sterilization wraps (woven and nonwoven). While most hospitals use all of these packaging options, the most commonly used method is sterilization wraps.
The original sterilization wraps were 140-thread count muslin cloth. Advantages of these cloths included that they were soft, reusable, inexpensive, absorbent, and drapeable (i.e., able to drape easily over trays). An important disadvantage was that the cloth was woven and, hence, did not provide complete protection against microbial penetration. To minimize microbial contamination of the instruments inside, hospitals initiated double sequential wrapping.
In the 1960s, nonwoven materials were introduced and provided an effective tortuous path that protected against microbial contamination and, when treated, provided liquid resistance capability. However, the material used for these wraps was derived from cellulose and did not possess adequate strength. Hence, sequential wrapping still remained necessary. The introduction of polypropylene allowed the development of wraps that possessed strength, barrier, and repellent properties.
Currently, a popular product offering uses a layered design consisting of spunbond/melt-blown/spunbond (SMS) layers. This fabric consists of three thermally bonded layers; "spunbond" provides the strength and "meltblown" provides the barrier. These multiple layers provide excellent protection from microbial contamination.2
In central processing, double wrapping can be done sequentially or non-sequentially (simultaneous wrapping). The sequential wrap uses two sheets of the standard sterilization wrap, one wrapped after the other. This procedure creates a package within a package. The non-sequential process uses two sheets wrapped at the same time so that the wrapping needs to be performed only once. This latter method provides multiple layers of protection of surgical instruments from contamination and saves time since wrapping is done only once. Multiple layers are still common practice due to the rigors of handling within the facility even though the barrier efficacy of a single sheet of wrap has improved over the years.
|Table 1. Characteristics of an Ideal Sterilization Wrap|
|Barrier effectiveness||Ability to prevent microbial penetration and maintain sterility of surgical pack and prevents penetration of liquids (i.e., repellent)|
|Penetrability (steam)||Allows steam to penetrate|
|Penetrability (e.g., ethylene oxide)||Allows sterilizing gases or plasmas to penetrate|
|Aeration||Allows aeration post-sterilization (e.g., allows ethylene oxide to dissipate)|
|Ease of use||Easy to use by personnel|
|Drapeability||Conforms to equipment pack contours smoothly and closely|
|Flexibility||Enough sizes to accommodate any sized or shaped item|
|Puncture resistance||Resists punctures|
|Tear strength||Resists tears|
|Waste disposal||Adheres to local and state solid waste disposal rules|
|Linting||Minimal linting during use|
|Cost||Low cost in use|
|Transparency||Allows verification of pack's internal contents before opening the pack|
Evaluating Shelf Life
Studies in the early 1970s suggested that wrapped surgical trays remained sterile for varying periods depending on the type of material used to wrap the trays.3-4 Microorganisms were found to penetrate single-wrap muslin as early as three days, and double-wrap muslin and single-wrap two-way crepe paper in 21 to 28 days when stored on open shelves.3 Based on these studies, the Joint Commission on Accreditation of Hospitals (now Joint Commission of Healthcare Organizations) required that hospitals provide an expiration date on wrapped surgical trays, indicating a time when the trays would no longer be considered sterile. In a 1984 article, Mayworm criticized the scientific basis for dating sterile surgical trays. He noted that "time doesn't contaminate products, events do."4 He then listed the following factors, which contribute to the contamination of product: bioburden (contamination in the environment), air movement, traffic, location, temperature, humidity, and the barrier properties of the wrap material. He stressed that when the proper wrap materials along with appropriate sterilization techniques were used, surgical trays should remain sterile unless damaged. Subsequent studies demonstrated that the sterile integrity of surgical packs was maintained for at least one year and no trend was found toward increased probability of contamination over time.5 In this latter study, no differences were observed among the wrapping materials studied (i.e., two-ply reusable, nonbarrier wovens, both new and previously used; disposable, barrier nonwovens; and paper/plastic peel pouches). These studies were conducted under ideal circumstances. Sterility may be more difficult to maintain under actual use conditions where movement and storage conditions may damage wrap materials.6
Characteristics of an Ideal Wrap
The characteristics of an ideal wrap are listed in Table 1.7,8 Key characteristics include the ability to allow the sterilizing agent (e.g., steam, ethylene oxide, hydrogen peroxide gas plasma) to penetrate and then to provide a barrier, which maintains sterility of the wrapped surgical instruments. Failure to allow the instruments to be sterilized and then to maintain their sterility may result in surgical site infections, clearly an unacceptable outcome. Other important desirable characteristics include drapeability, puncture resistance, resistance to tearing, liquid resistance, flexibility, non-reactive, non-linting, non-toxic, stable, no odor, easy to use, transparency, non-restrictive waste disposal, and low cost in use.
Evaluating a Sterilization Wrap
In evaluating wrap products, professionals should evaluate the products based on performance characteristics. The data provided on products should be based on standardized tests and, when possible, be confirmed by independent laboratories. Products may not possess all the characteristics of the "ideal" wrap. Professionals may need to balance the importance of individual characteristics. The intended use of the product in the professional's facility must be assessed. Lastly, the cost and time of training personnel must be considered in the decision to purchase a new product.
Table 2. Questions to Ask in Evaluating a Sterilization Wrap
|Characteristic||Possible Test Methodology|
1. Has the manufacturer assessed linting of the wrap?
Resistance to linting (Gelbo Lint)
INDA Std Test Method 160.1-92
1. Can the manufacturer provide data that the wrap allows steam penetration?
Fractional Kill Steam Penetration
Test/Routine BI Monitoring
|2. Can the manufacturer provide data that the wrap allows ethylene oxide penetration and permits 100% sterilization within the minimum cycle times recommended by AAMI?||
Minimal cycle Ethylene Oxide (EO)
Penetration Test /
Routine EO BI monitoring
|3. Can the manufacturer provide data that the wrap allows hydrogen peroxide/gas plasma penetration?||
Hydrogen peroxide Penetration
Test / Routine BI monitoring
1. Can the manufacturer provide data that the wrap allows aeration (i.e., allow toxic sterilizing gases to dissipate)? Levels should be below the maximum levels permitted by the FDA guidelines.
|Ethylene Oxide Residuals Analysis|
1. Has the puncture resistance and tear strength of the wrap been assessed using an appropriate methodology?
|Grab Tensile - ASTM Test Method D 5034-90; Federal Test method Standard No. 191A, Method 5100.|
Microbial Barrier Effectiveness
1. Can the manufacturer provide current event-related sterility maintenance information on the sterilization wrap?
2. Can the manufacturer provide current time-related sterility maintenance information on the sterilization wrap?
3. Have sterility maintenance studies been conducted by an independent laboratory?
|Event-related sterility maintenance studies and time-related shelf life studies conducted by independent laboratories and as reviewed in the literature.|
|4. If the product is reusable, can the manufacturer provide sterility maintenance information on the wrap up to the maximum number of recommended wash cycles (event-related and time-related)?||As above|
|5. Has the microbial penetrability of the wrap been tested using standardized procedures?||Dry spore Talc Challenge Test|
|6. Does the wrap provide an adequate barrier to penetration by liquids?||Hydrostatic Head Test - Federal Test Standard 191A, Method 5514|
Does the wrap fold away from the surgical pack and not snap back once opened?
ASTM D 5732-95
In cases where an appropriate recycler can be located, is the wrap recyclable?
Currently available products for wrapping surgical instruments are clearly superior to older products. The characteristics of an ideal wrap are well described. Professionals must evaluate individual wraps based on intended use in their facility. New wrap materials are constantly being introduced into healthcare; however, they should be evaluated by using the guidelines provided in this paper.
William A. Rutala, PhD, MPH, and David J. Weber, MD, MPH are from Division of Infectious Diseases, University of North Carolina (UNC) School of Medicine and the Department of Hospital Epidemiology, UNC Health Care System (Chapel Hill, NC). This paper was supported, in part, by an educational grant from Kimberly-Clark. The authors would like to thank Jan Schultz for reviewing this article.