Your first-line-of-defense against Preventing Corrosion is maintaining the passive layer of Surgical Instruments. Stainless steel surgery 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 surgery instruments as corrosion resistant as possible. It is imperative that you maintain the passive oxide layer to prevent corrosion and maintain your surgery instruments in optimal condition. If this is not done the stainless steel will be more susceptible to corrosion, pitting and stains.This will reduce the life of the surgery instruments and/or render it useless. Initially, 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 surgery instruments and surgical instrument containers recommend the use of neutral pH cleaning concentrates. Newly developed neutral pH all-in-one or "combination detergent" 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 surgery instruments. Cleaning concentrates with a high or low pH have been shown to erode the passive layer. The most common of these cleaning concentrates utilize an alkaline detergent with an acid neutralizer. Virtually all manufacturers of surgical instruments and surgical instrument containers recommend against using these detergents and recommend using a neutral ph detergent. More information and studies regarding the passive oxide layer of Surgical Instruments is below.
Interpreting Rust Yellow-brown to Dark-brown STAINS or Spots when Cleaning Surgical Instruments and Cleaning Endoscopes Yellow-brown to dark-brown stains or spots on surgical stainless steel instruments are frequently mistaken for rust. These residue deposits (stains or spots arranged in groups or along edges or in crevices) are usually the instrument being exposed to result of high chloride content. They will lead to pitting of the surgical instrument surface if not removed. (see Avoiding High Levels of Chloride below) Excessively hard water can contain high levels of salt sufficient to cause stains or spots that appear as rust. Boilers used to generate the steam for steam sterilizers, if not cleaned properly, will produce contaminated steam which can deposit minerals onto instruments during the sterilization process.
use neutral pH cleaning agents, dry and cool instruments as soon as possible following cleaning & sterilization treatments, whenever possible use purified water (DI or RO) to thoroughly rinse instruments prior to drying & sterilization, avoid exposing the surface protective layer of the instrument to abrasive conditions & treatments, minimize the time instruments are exposed to high temperatures, and avoid using agents containing chloride (do not exceed ~ 120 mg/l, 200mg/l NaCl Sodium Chloride - Salt).
A common problem is the inadvertent use of NaCl Sodium Chloride - Salt containing solutions do 'soaking instruments in surgery to maintain hydration of debris and prevent encrustation.
ALSO AVOID using cleaning agents containing other halogen ion agents (e.g. iodides, bromides).
Use cleaning agents containing "Nonionic Surfactants" whenever possible.
Neutral pH Cleaning Concentrates recommended by Device Manufacturers
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 abrasive Cleaning Concentrates , which will scratch the surface allowing dirt and water deposits to collect. Abrasive cleaning will remove the protective passive layer.
Do not use Cleaning Concentrates with 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 or "Source" Water when Cleaning Surgical Instruments and Cleaning Endoscopes: 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. Cleaning, Conditioning, Disinfection Sterilization of Surgical Instruments when Cleaning Surgical Instruments and Cleaning Endoscopes: Clean instruments, or apply treatment to prevent the drying and encrustation of debris, 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 enzyme-detergent or apply an enzyme-detergent foam spray to delay drying. The use of pre-soaking enzyme-detergent foam sprays have 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" cleaners and the enzyme-detergent foam sprays deliver a chemical complex to: maintain the hydration of bioburden, prevent corrosion, clean the surface, and condition the surface of instruments & scopes. This can significantly reduce manual cleaning and facilitate cleaning the surface of surgical instruments, scopes, and the lumens of cannulated instruments inside-and-one. If used properly, all-in-one enzyme detergent foam sprays and/or all-in-one "combination" cleaning concentrates can render excellent outcomes and facilitate cleaning instruments and scopes inside-and-out. They effectively cleaning the surface while cleaning lumens and working channels. This can eliminate or reduce the manual labor expended, rendering lower reprocessing costs while improving turnaround.
Cleaning 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 surgery instruments may crack or rupture the plating. Ultrasonic Cleaners do not provide the complete "proper sequence of treatments" i.e. purified final rinse(s) that are purified, purged between treatments 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 most effective when used with hot water per manufacturer’s recommended temperature and with "high level" multi-tiered enzyme 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 surgery instruments in an ultrasonic cleaner since the ultrasonic vibration and the presence of other sharp instruments may crack or rupture the plating. Always refer to the printed manufacturer recommendations prior to using Ultrasonics.
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. "all-in-one" cleaning concentrates 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 surgery instruments during storage.
Staining and spotting may result if residual chemicals are not completely rinsed from surgery 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 to prevent stains and spots. A Cleaning Concentrates that will avoid spotting are "free-rinsing" or "rinse clean". 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 concentrates 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 surgical instrument 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. How is the "passive oxide layer" manufactured and maintained during the cleaning of Surgical Instruments and the cleaning of Endoscopes? 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, by the manufacturer, is a process used to achieve a smooth surface on the instrument. Surgical Instruments are polished 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 surgery instrument. Proper cleaning, handling, and sterilization will build up the layer of chromium oxide and protect the Surgical Instrument from corrosion and /or pitting. In some circumstances older instruments have higher resistance to corrosion than new ones. The newer instruments have not had the time to build up the chromium oxide layer. Improper cleaning and sterilization can cause the layer of chromium oxide to disappear or become damaged thus increasing the possibility of corrosion and/or pitting. Proper cleaning and sterilization can cause the layer of chromium oxide to improve over time thus decreasing the possibility of corrosion and/or pitting. Second only to the financial asset value of the working staff, the surgery instrument and scope inventory is the single most financially valuable asset of the healthcare facility. It is important to properly clean, sterilize, handle, and store your instruments.
John Temple, Product Development