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Hi Tristan,
You have asked a very good question. The purpose of a shelf life policy is to protect the patient from unsafe products. Some items, such as some types of suture, degrade naturally over time and have a shelf life that is based the rate of decay. Instrument sets containing metal instruments are a different class of device because under normal circumstances one does not expect the instruments to decay. The primary concern with instrument sets is the sterility of the contents. The wrapper or container protect the instruments inside from microbial contamination. Why does the wrapper or container protect the instruments on one day, but not on the following day? Why does it fail? Can the microbes read the date and know to stay out until after the expiration date?
In 1982 I took over a storeroom that had previously belonged to the Surgery Department. (University of Iowa Hospitals and Clinics) I found sets of surgical instruments from 1945 wrapped with newspaper sitting on the shelves. These sets had over one quarter inch or one centimeter of dust sitting on top of them. On a whim, I brought one of the sets to the Clinical Microbiology lab. We opened the set and they tested the instruments. They were still sterile after sitting undisturbed on the shelf for 37 years! Why didn't the old brittle newspaper fail as a protector of sterile instruments?
It turns out that the answer has to do with the handling of the wrapper or container. These sets had sat undisturbed since the day they were sterilized. When the sterile device is sitting undisturbed, the wrapper is not challenged and the device remains sterile. Handling of the set is when the wrapper may be compromised. Imagine a magnified image of a muslin wrapper. Between the threads are holes. When the wrapper is squeezed and then released, air is forced in and out of the package which can blow micro-organisms into the package. If the wrapper gets wet, micro-organisms can swim right through the paper or cloth wrappers. Dragging a set from a shelf instead of lifting the set from the shelf can force micro-organisms through a wrapper. If a heavy package is dropped, then micro-organisms can be forced through the wrapper. (Experiments have shown this rarely happens with peel-packaged items under 100 grams dropped from table height.)
The types of events listed above create the potential for the wrapper or container to fail. In the past it was believed the safest policy was to assume every item processed by the sterilization team would be handled a minimum of three to five times a week. With the low quality of protection offered by the standard muslin wrappers, this meant an item should be considered as potentially contaminated after a set time - 1 month, 3 months, 6 months; whatever the hospital Infection Control department felt comfortable with. Today, many hospitals have decided to use what is called "Event Related Sterility". This involves a large investment in educating every person in the hospital in understanding what type of events can potentially compromise the wrapper. They also have to know to send the item back for reprocessing! This educating of the staff is easier to do today because the quality of the available wrappers is better than the cloth wrappers used in the past. The modern wrappers work better at protecting items, so the level of control can be relaxed a little. Even better are container systems. With rigid instrument containers, there is almost zero chance of a tear or a hole in the wrapper because the filters are well protected! This is a giant step forward compared to putting a piece of paper or muslin cloth around a set. The return on the investment is that no items are reprocessed unless something happened to the item to potentially compromise the wrapper. With this system, the items are labeled with the load number and sterilizer ID number and the sterilization date. No expiration date is given. I believe a wise material manager will still want to do periodic date checks of items; not for sterility concerns, but to know if the investment is being used well. One of many ways to do this can be to use a one year expiration date and have the staff report all expired items to the manager. A set or pack that sits for a whole year without being used might be an underutilized investment. Perhaps tearing the set down and using the components in frequently used sets might be a better option than having the item remain where it is.
I hope this sheds a little light on the mystery of expiration dating in hospitals.
Regards, Pete Bobb
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