NO MAGIC NUMBER FOR INSTRUMENT-SET WEIGHT
By Becki Harter, CST, RCST. CRCST, FEL
Over the years, many articles have been writtenon the management of instrument-set weight in the central sterile/sterileprocessing (CS/SP) department. Regulatory standards and professional clinicalorganizations have published the no magic number concept for instrumentset(s) in the sterilization process for years, giving the reader the idea thatthe weight of the instrument set(s) did not really matter in the overallprocess. I have struggled to make this concept work in clinical practice andfound the battle too daunting to win. Instrument sets that exceed therecommended weight by manufacturers of sterilizers have created and continue tocreate hardships in CS/SPD such as (but not limited to):
Now multiply that by all the sets that areprocessed in a shift and your personnel have the potential to lift theequivalence of 3,500 to 4,700 pounds in one shift.
I began to research the issue of weight and foundthat there is, indeed, no magic number but that there is a number supported byscientific data that supports SAL requirements for our patients safety. Therecommended weight of 16 to 20 pounds comes from the physical properties andrequirements to achieve SAL of 10 to the minus six in a sterilization process. Ifound that the healthcare environment largely misunderstands or does not knowthe importance of weight in the sterilization process. All forms ofsterilization have specific weights by which SAL is measured and achieved.Whereas weight is not the only factor, it is a very important factor in asuccessful sterilization process. The idea that SAL can be achieved simply byplacing items in a sterilizer and pressing a button and sterilization magicallyoccurs no matter what is placed inside the sterilizer is dangerous and cannot besupported by scientific data to be true.
To understand the importance of a 16 to 20 poundweight limit for instrument set(s) we must go back to the beginning. Beforegravity displacement, dynamic air removal or steam-flush pressure pulse steamsterilizers, dry heat, convection heat and ETO/EO or plasma sterilizers therewas a sterilization unit that worked much like a pressure cooker. It had a valveto release pressure and a gauge to measure that pressure. Once the pressure hadreached the set-upon point for a specific amount of time, the valve was releasedand the cycle was completed. But there was no real data to support terminalkill, just that a terminal kill process had occurred and an assumption or hopebased on basic principle was that any viable microorganisms were killed andwould not cause infection or harm in patients.
This practice has been abandoned because ofscientific growth and understanding of microbial growth; what kills and whatdoes not at a specific rate (F value) at a specific time (D value). The standardhealthcare sterilization cycles we have today are based upon how long it takesat a specific temperature to kill microorganisms at a 10 to the minus sixth logthat has been determined not to produce disease in the compromised tissue ofpatients.
Moisture requirements for instruments in steamloads are minimal, and only in few cases is moisture added to an instrument tofacilitate the sterilization process (i.e., it is recommended that sterile wateris added to cleaned/disinfected lumen instruments in gravity displacementsterilizers prior to sterilization by instrument manufacturers). As a standard,however, moisture in or on instruments prior to a steam sterilization process isnot recommended because moisture can create a growth medium for microorganismand has the potential to form a biofilm on instruments. Moisture found in setspost-sterilization for wrapped sets or sets in closed containers is notrecommended because of the possibility the set can become contaminated andbecome the breeding ground for microorganisms.
Remember, most microorganisms need three thingsto grow: warmth, moisture and a dark environment. All three of theserequirements are met inside of a wrapped sterilization tray or in a closedcontainer if standards of practice are not followed. But where does the weightcome in and why does it matter?
Once time and temperature parameters weredetermined it had to be determined what kind of set load would best support theSAL. In that process it was found that a set containing 99 instruments that didnot exceed 15 to 17 pounds best supported the SAL level and minimized the riskof wet packs related to set density and configuration. Autoclave manufacturerstest our sterilizers with a 16-pound test pack and have based the standardhealthcare cycles on that data. Whereas a set can weigh greater than 16 to 20pounds and can be validated in a sterilization cycle, the sterilization cyclesrequired to achieve SAL in a set weighing over 20 pounds often requires a cyclethat falls outside of what is achievable in healthcare and falls outside thepublished standard healthcare cycles preset by autoclave manufacturers thatfollow the healthcare standard based upon scientific data to support a 10 to theminus sixth log of kill.
The argument has been submitted that cycles canbe changed. This is true; they can be changed. But your autoclave manufacturerwill not stand behind any cycle that it has not validated and if a healthcaresystem chooses to go outside of what the sterilizer manufacturer has recommendedand pre-set, the healthcare system must validate that process according to AAMIST8 guidelines.
CS/SPDs do not validate but verify parametersusing biologicals such as Bowie Dick or Dart test and indicators/integrators.Healthcare device manufacturers validate medical devices and healthcare verifiesthat according to published standards of practice. If an SPD decides to operateand accept medical devices that fall outside the standard it must accept allliability and it is worth noting that your warranty on your sterilizer (ifapplicable) will be void. In addition, by operating outside the standardhealthcare cycles to include standard weights, you could be causing yourfacility to violate federal, state and local regulations and jeopardize yourfacilities insurance coverage.
The standard cycles that we have in healthcaretoday are based on the SAL of 10 to the minus six. If instrument sets aregreater than 20 pounds, they must be validated for SAL, which will be difficultto do within the published standard healthcare cycles because they are based ona maximum weight of 16 to 20 pounds. There is no doubt in this consultantsmind that if we as a healthcare industry do not adhere to all standardsconcerning sterilization to include:
Guidelines for sterilization to include weightrequirements/ recommendations are found in:
Out of all the reasons we should, to include:
There is one reason that stands out among themall, and that is our patients safety. Every manufacturer or healthcareprofessional, who has ever said that there is no magic number for weightfor sterilization of instrument set(s), is correct. The number is not magic atall and it never has been. However, the way weight has been dealt with in thepast has treated the sterilization process like a Houdini in that the assumptionwas made that weight of any proportion did not bear any negative consequence inthe sterilization process. It has been assumed that we can place any proportionof weight and density in a sterilization process and abracadabra it comesout sterile! Not so. It is based upon scientific data that supports SAL and morecritically, positive patient care outcomes.
What is the magic number? There isnt one. Butwhat is the actual number? Its 16 to 20 pounds. Its not magic. It is a hatof scientific principles with a wand of supporting data on a table spread withthe standards of practice with an audience of patients that depend on us fortheir safety.
Becki Harter, CST, RCST, CRCST, FEL, ispresident/CEO of Indianapolisbased Sterilization by Design and is the 2003winner of the AAMI Becton Dickinson Career Achievement Award.