The ever present intensity of the pressures that have been exerted on the entire healthcare provider community to control, let alone reduce its operational costs has not spared any department or individual practice from scrutiny. One of those practices was that of the time-related shelf-life policy of sterile packages.

Although there does not appear to be any documented evidence as to how a specific period of time was originally selected for the time-related policy, there is reason to believe that the 30 day period that appears to have been universally adopted may have been established by a study done by the Centers of Disease Control and Prevention more than 30 years ago.1 Once the package exceeded the time-related (30 day) expiration date, the practice called for the package to be opened, broken down, re-assembled and re-wrapped and then sterilized a second time.

In an attempt to eliminate the costs associated with the reprocessing of those outdated packs, many hospitals converted to the event-related shelf-life policy. In their recent sterility assurance document, the Association for the Advancement of Medical Instrumentation (AAMI) defines shelf-life as "event-related and depends on the quality of the packaging material, the storage conditions, the conditions during transport and the amount of handling...There should be written policies and procedures for how shelf-life is determined and how it is indicated on the product".2 (It should be noted that the time-related principle is not even given honorable mention in the document.)

Principles of event-related versus time-related shelf-life

The manufacturers of prepackaged sterile medical devices have been using the principles of event-related shelf-life policy for a prolonged period of time. But the situation in a hospital setting is simply not quite the same. What is over-looked is that the manufacturers’ method of sterilization enables them to use packaging materials that possess the maximum protective capability available and makes it possible for them to say that the "contents are sterile until package is opened or the packing material is damaged". Under those circumstances, the maintenance of sterility is truly event-related.

Thus it seemed reasonable to believe that if hospitals were to be able to replicate the manufacturers’ event-related warranty, the most critical component of their packaging practices that had to be changed was that of the wrapping/packaging material.

As reasonable as that may appear to be, what is interesting is that for all the years that the time-related policy had been used, there have only been two studies published in which the researchers have reported their findings on its effectiveness.

Studies on the qualities of wrapping materials

The first comprehensive study examined the influence that four different qualities of wrapping materials had on the maintenance of sterility of the packs’ contents. Included were peel pouches, both new and used two-ply woven non-barrier reusable wrappers and a non-woven (disposable) barrier quality wrapper. All packages contained either five towels or two surgical gowns and all were sequentially double-wrapped. At monthly intervals for a year, randomly selected packs from each wrapping-storage combination were removed for sampling. Although peel pouches were found to have the lowest contamination probability and used, non-barrier woven wrappers the highest, the difference in the probabilities of contamination between the two was NOT statistically significant. Thus, in terms of event-related shelf-life, the group concluded that storage periods of up to 50 weeks for the double-wrapped packages did not increase the probability of contamination regardless of the wrapping material used.3

In the second study, the same kind of non-barrier, reusable woven wrapper material produced rather unexpected results. In this instance, the researchers were attempting to determine the shelf-life of surgical instrument trays to support the establishment of an event-related shelf-life policy. Six hundred (600) samples on 100 surgical trays, each weighing 15 pounds, were tested. Each tray was sequentially double-wrapped with two 2-ply, reusable, non-barrier quality wrappers. When unloading the cart following sterilization, the back end of the tray was slid from the cart toward the storage shelf where it was permitted to drop approximately 4 inches. The investigators reported finding contamination in only 5 of the 600 samples - a remarkably low rate of .83 percent!4

It is to be noted that in both of these studies, the packs and trays were sequentially double-wrapped. Interestingly enough, the transition from a time-related to an event-related shelf-life policy has challenged the need and/or purpose for doing so. It is reasoned that the new generation of wrapper materials provide the same level of ‘barrier’ protection as that provided by double-wrapping. Of course, from the perspective of cost, single-wrapping eliminates the cost of labor associated with wrapping the package a second time.5

Purpose of double-wrapping

Overlooked in the interim is the original purpose for double-wrapping, which actually is not related to the maintenance of sterility while the package is in storage.

The purpose of the second wrapper is succinctly explained in the renowned Perkins text as follows:

• "Any package in storage will, sooner or later, collect a layer of dust particles on the wrapper making it difficult if not impossible to open the package without danger of contaminating the contents. A double wrapper is essential for packs destined for the operating room or any specialized area in the hospital where asepsis is practiced. The outer dust-protective wrapper should be removed before the pack is admitted to the clean zone".6

One could reasonably conclude that sequential double-wrapping should be an integral part of an event-related shelf-life policy. After all, the longer a package is stored, the greater the likelihood for dust to accumulate and the greater the probability or possibility of contamination. Then, too, the longer the shelf-life, the greater the opportunity for mishandling and exposure to environmental conditions. Under the circumstances, if a particular quality of wrapper material is considered to be an effective ‘barrier’ as a single layer, then there really is no need for the second or outer wrapper to be of equal/like quality. A lesser quality should suffice.

At this point, the question that logically arises focuses on the need for a change from time-related to event-related shelf-policy to be accompanied by both an upgrading in the quality of the packaging material and changes in the wrapping practices.

Other than the two studies cited herewith, it seems that few clinicians, if any, ever undertook the arduous task of determining whether their in-house processed items remained sterile for less than 28 days, or possibly for even 45 to 60 days, and understandably so. Shelf-life testing requires scientifically sound protocols and careful execution, and even so, can be an imprecise venture under the best circumstances. Furthermore, central supply departments are neither equipped nor have the capability to do the sterility testing that would evaluate safe storage times for the myriad of wrapping materials that industry has made available in today’s competitive marketplace. As a result, most of the information upon which an event-related policy may be implemented could be predicated on data developed in a laboratory under controlled conditions rather than on those found in a realistic type of situation.

Sterilization wrap as Class II medical device

At the moment, in the Code of Federal Regulations (CFR) the Food and Drug Administration (FDA) has classified ‘Sterilization Wrap’ as a Class II medical device which it describes as follows: "A sterilization wrap is a device intended to be used to enclose another medical device that is to be sterilized by a health care provider. It is intended to allow sterilization of the enclosed medical device and also to maintain sterility of the enclosed device until used".7 It is further to be noted that as a Class II medical device, performance standards are required. Yet, as of this date, no test(s) has been sanctioned by either a governmental organization or professional/industry association, i.e., AORN, AAMI or ASTM, that could be used to demonstrate the protective capabilities of a wrapping material. Under the circumstances, even if there is a need for the quality of the wrapping material to be upgraded, on what basis is that to be done?

A perfect wrapper

A perfect wrapper would be one that is impervious to extraneous microbes, liquid-proof, free of holes, free of lint, free of memory, strong enough to resist punctures and tears and economical to use. Theoretically, it would be capable of protecting a sterilized product indefinitely. Unfortunately, such wrapper materials also would impede both the passage and withdrawal of the sterilizing agent.

Whatever the changes made in prevailing practices, it is vital that they be viewed from a cost-benefit perspective. If a time-related shelf-life program has been in effect and there have not been any problems with the sterility of the products put into service, there may not be a reason for a wholesale changeover to an event-related policy — let alone any change in wrapping practices.

In those instances where the record indicates certain items are repeatedly being reprocessed because of their being ‘out-dated’, a change in the packaging method may be in order, such as, the use of dust covers. Then again, the situation may be one that could be easily remedied by an adjustment in inventory levels.

1) Standard, PG, Mackel, DC and Mallison, GF, Microbial penetration of muslin and paper-wrapped sterile packs stored in open shelves and in closed cabinets, Applied Microbiology, 1971, 22, 432-437.

2) Steam Sterilization and sterility assurance in healthcare facilities, American Standards National Institute (ANSI)/AAMI ST 46:2002, Section 5.9.4, p. 38, AAMI, Arlington, VA.

3) Klapes, NA, Greene, VW, Langholtz, AC and Huntsiger, C, Effect of Long Term Storage on Sterile Status of Devices in Surgical Packs, Infection Control and Hospital Epidemiology, 1987, Vol 8, 289-293.

4) Widmer, AF, Houston, A, Ballinger, E & Wenzel, RP, A New Standard for Sterility Testing for Autoclaved Surgical Trays, Journal of Hospital Infection, 1992, Vol. 27, pp. 253-260.

5) McCormack, J, Who says two wraps are better than one?, Materials Management in Health Care, 1995, 4, p. 52.

6) Perkins, JJ, Principles and methods of sterilization in health sciences, 2nd edition, 1973, Charles C. Thomas, Springfield, IL, p. 203.

7) CFR 21, Parts 800 to 1299, Revised as of April 1, 2002, Item No. 880.6850 p. 399.