Care of General and Specialty Surgical Instruments
Stainless steel surgical instruments are made of corrosion resistant high-grade specialty steels. The key word here is “resistant”. Corrosion resistant does not mean corrosion proof. One of the special characteristics of these steels is that the manufacturer forms a "passive oxide layer" on the surface, which protects them against corrosion. This makes surgical instruments as corrosion resistant as possible. It is imperative that you must maintain the passive oxide layer to prevent corrosion and maintain your surgery instruments in optimal condition. If this is not done the stainless steel can corrode or stain which can reduce the life of the surgical instrument or render it useless. All “stainless steel” surgical instruments have the same corrosion resistance. When strength and hardness requirements are important factors for instrument function, corrosion resistance is generally lower. Increasing the corrosion resistance would soften the stainless steel. Manufacturers of surgical instruments and surgical instrument containers recommend the use of neutral pH cleaning concentrates. Newly developed neutral pH all-in-one or "combination" cleaning concentrates have been shown to be effective in optimizing the efficacy of the "passive oxide layer". This will provide a longer life for stainless steel surgical instruments. More information and studies regarding the "passive oxide layer" of Surgical Instruments is below.
Virtually all manufacturers of surgical instruments, rigid scopes, flexible scopes, and instrument containers recommend the use of neutral pH cleaning concentrates. Generic Example of this recommendation: Do not use high acidic (pH <4) or high alkaline (pH >10) products for disinfection or cleaning, since these can corrode metal, cause discoloration or stress fractures.
Do not use abrasive pads or cleansers, which will scratch the surface allowing dirt and water deposits to collect. Abrasive cleaning will remove the protective passive layer.
Do not use high concentrations of chlorine bleach to clean or disinfect stainless steel instruments, as pitting will occur. Never use bleach to clean any surgical instruments. The high pH of bleach causes surface deposits of brown stains and might even corrode the instrument. Even high quality stainless steel is not impervious to an acidic bleach solution.
Sort instruments by similar metal for subsequent processing so that electrolytic deposition (galvanic corrosion) due to contact between dissimilar metals will not occur.
Tap water can contain many minerals, which may discolor and stain surgical instruments. It is recommended that de-ionized water be used for the final rinsing to prevent spotting. all-in-one or "combination" cleaning concentrates can be effective in treating unacceptably hard source water and removing hard water encrustation from surgical instruments and equipment. If untreated tap water is used for final rinsing, then the instruments must be dried immediately to avoid staining.
Clean instruments as quickly as possible after use. Do not allow blood and debris to dry on the instruments. If cleaning must be delayed, place groups of instruments in a covered container with appropriate detergent or enzymatic solution to delay drying. The use of pre-soaking enzyme detergent foam spray has been shown to reduce the time expended for manual cleaning and render higher quality outcomes. After surgery, open all box locks and disassemble instruments with removable parts. This will limit blood drying on instruments that may cause them to corrode. The "all-in-one" pre-soak & cleaner foam spray delivers a chemical complex to: maintain hydration of bioburden, prevent corrosion, clean the surface, and condition instruments & scopes. This will significantly reduce manual cleaning and facilitate cleaning lumens inside-and-one. Enzymatic detergent foam spray and/or all-in-one "combination" cleaning concentrates render excellent outcomes and facilitate cleaning instruments and scope inside-and-one, effectively cleaning the surface while cleaning lumens and working channels. This can eliminate or reduce the manual labor expended, rendering lower reprocessing costs and improving turnaround.
Cleaning is the Prerequisite for Sterilization
The reprocessing decontamination process, whether done manually or automatically in a washer-decontaminator- disinfector, can only be effective if cleaning is adequate. Effective disinfection or sterilization: (Generic Sterilization with a Pre-Vacuum Sterilizer (HI-VAC): 270-272° F (132-134° C), 16-minute exposure time, with 4 pulses and a 30-minute dry time. Generic Sterilization with a Gravity Displacement Sterilizer: 270-272° F (132-134° C), 30-minute exposure time, with a 30-minute dry time.) Sterilization of an inadequately cleaned instrument is not possible. Cleaning is the prerequisite for sterilization.
Ultrasonic cleaners are very effective when used with hot water per manufacturer’s recommended temperature and specially formulated detergents. It is recommended that all visible debris and blood be removed from the instrument prior to ultrasonic cleaning. Contact between dissimilar metals can cause corrosion when ultrasonics is applied. Sort surgical instruments according to similar metal types to prevent corrosion. (electrolytic deposition - galvanic corrosion) It is not recommended to clean plated instruments in an ultrasonic cleaner since the ultrasonic vibration and the presence of other sharp instruments may crack or rupture the plating. Ultrasonic Cleaners are not as effective as washer decontaminators in providing the complete "proper sequence of treatments" i.e. final rinse(s) that are purified and/or have temperatures elevated to disinfection levels. Ultrasonic Cleaning can effectively remove: long term encrustation and surgical cements or glues that have dried onto instrumentation. Overloading, and low water temperature, will decrease the effectiveness of ultrasonic equipment.
Ultrasonic cleaners are effective when used with hot water per manufacturer’s recommended temperature and specially formulated detergents. It is recommended that all visible debris and blood be removed from the instrument prior to ultrasonic cleaning. Sort instruments by similar metal for subsequent processing so that electrolytic deposition (galvanic corrosion) due to contact between dissimilar metals will not occur. It is not recommended to clean plated instruments in an ultrasonic cleaner since the ultrasonic vibration and the presence of other sharp instruments may crack or rupture the plating.
To maintain moving parts and protect instruments from staining and rusting during sterilization and storage, they should be lubricated with a water-soluble, preserved lubricant after each cleaning. Most automated washer decontaminators provide the option for lubrication at the end of the final rinse treatment. Since effective ultrasonic cleaning removes all lubricant, re-lubrication is important. A complete "all-in-one" cleaner will provide lubrication. The lubricant should contain a chemical preservative to prevent bacterial growth in the lubricant bath. The bath solution should be made with de-mineralized water. A lubricant containing a rust inhibitor helps prevent electrolytic corrosion of points and edges. Immediately after cleaning, instruments should be immersed or rinsed for 30 seconds and allowed to drain off, not wiped off. A lubricant film will remain through the sterilization to protect them during storage.
Staining and spotting may result if residual chemicals are not completely rinsed from instruments that are subjected to steam sterilization. Following the manufacturer’s recommendations for the proper sequence of treatments (cold water pre-wash, enzyme/detergent wash, purified water rinse/lubrication, and drying) is critical in preventing of staining and spotting. Cleaning concentrates should be "free-rinsing" to avoid spotting instruments.
Studies regarding the "passive oxide layer" of Surgical Instruments
(Guidelines on metals and alloys in contact with food; Council of Europe; published 11.10.2000. Systemic nickel: the contribution made by stainless steel cooking utensils; Contact Dermatitis, Volume 32:2, 1994) of the stainless steel passive layer to prevent corrosion have revealed a reduction in corrosion prevention with the use of cleaning concentrates that are not neutral pH. The use of cleaning agents that deliver an acid rinse will release nickel from the stainless steel and decrease the efficacy of the passive layer. This is most critical on initial reprocessing events of stainless steel surgical instruments. Measurable levels of nickel have been detected. It was also shown that, as the number of subsequent uses increased, the level of nickel release diminished and reached a steady state (measured in the order of μg/l). These observations reflect the changes that occur in the passive oxide layer on first immersion of stainless steels in aqueous media.
What is Stainless Steel ?
Stainless steel is essentially a low carbon steel which contains chromium at 10% or more by weight. It is this addition of chromium that gives the steel its unique stainless, corrosion resisting properties. The chromium content of the steel allows the formation of a rough, adherent, invisible, corrosion-resisting chromium oxide film on the steel surface. If damaged mechanically or chemically, this film is self-healing, providing that oxygen, even in very small amounts, is present. The corrosion resistance and other useful properties of the steel are enhanced by increased chromium content and the addition of other elements such as molybdenum, nickel and nitrogen. Stainless steel has a passive film created by the presence of chromium (and often other alloying elements, nickel, molybdenum) that resists this process. When exposed in air, stainless steels passivate naturally (due to the presence of chromium). But the time required can vary. In order to ensure that the passive layer reforms rapidly after pickling, a passivation treatment is performed using a solution of nitric acid and water.
The passive layer or stainless steel is intended to prevent or resist corrosion. The process is called “Passivation”. “Passivation” and Polishing eliminate the carbon molecules form the instrument surface. This forms a layer which acts as a corrosive resistant seal. Passivation is a chemical process that removes carbon molecules from the surface of the instrument. This chemical process can also occur through repeated exposure to oxidizing agents in chemicals, soaps, and the atmosphere Polishing is a process used to achieve a smooth surface on the instrument. It is extremely important to polish an instrument because the passivation process leaves microscopic pits where the carbon molecules were removed. Polishing also builds a layer of chromium oxide on the surface of the instrument. Through regular handling and sterilization the layer of chromium oxide will build up and protect the instrument from corrosion. In some circumstances, that is why you will notice older instruments less corrosive than new ones. The newer instruments have not had the time to build up the chromium oxide layer. However, improper cleaning and sterilization can cause the layer of chromium oxide to disappear or become damaged thus increasing the possibility of corrosion. That is why it is so important to properly clean, sterilize, and store your instruments.
John Temple
Product Development
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