REUSABLE MEDICAL DEVICES
An important note is that enzymatic detergents that contain multiple enzymes, i.e. protease, amylase and lipase may be unstable in the presence of one another; studies have shown relatively rapid destruction of one enzyme by another enzyme in as little as a few months’ storage at room temperature; this degradation may be much faster at elevated temperatures. Alkaline detergents are detergents that contain alkalis as well as surfactants. These alkaline detergents are so-called as they form a solution in water that is high in pH, typically greater than pH 10; they usually contain metal hydroxides such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), producing the hydroxide ion (OH-) in aqueous solution. These detergents demonstrate high efficacy at removing fats, oils and proteins, as the alkali results in hydrolysis of large proteins and lipids, breaking them into smaller water soluble pieces. They are more effective at higher temperatures (greater than 60˚C), but high pH and high temperature may have material compatibility issues (i.e. alkaline corrosion), however this is very much dependent upon the concentration used. Another interesting aspect of alkaline detergents is that they have shown to be capable of the inactivation of prion proteins. Neutral detergents are detergents that form a solution in water that is near neutral pH, typically between 6.5 to 8 (with pH 7 of course being neutral). These detergents are normally used as a two-part cleaning regime – firstly an enzymatic detergent is used, followed by a neutral detergent. These are typically used as an alternative to alkaline detergents where material compatibility could be an issue; as well as being less aggressive than alkaline detergents, there is usually an increased cycle time and a need for a higher temperature for equivalent cleaning efficacy.
Sequestrants and chelating agents
In order to allow a greater spectrum of detergent efficacy in a range of water quality supplies, certain chemicals can be added to addresses these negative effects of hard water and metal ions. These chemicals are typically known as sequestrants. These sequestrants have a specific chemical structure that allows them to bond or react with metal ions in the hard water. A specific form of sequestrant is known as a chelating agent; these chelating agents have a structure like a claw which can bind the free metal ions, and hence make water act as though the metal ions (that impart water hardness) were not present, thus enhancing the effects of the detergent system used. The ions for which chelates are particularly useful are multivalent ions such as Ca, Mg, Fe, Cu, Zn, Ni etc. Chelates typically prevent deposition onto instruments and allow the detergent to perform the cleaning as expected. They can also inhibit scale formation and remove scale deposits, as well as destabilise secondary protein structures and hence contribute towards cleaning. It is important to note that the best
Reduce unnecessary wear and tear in your washer-disinfector with Prolystica HP cleaning chemistries.
chelant or sequestrant for the system is not always the one that can handle the most water hardness; a combination of at least one chelant and at least one sequestrant can typically outperform each individual component. Chelants perform stoichiometrically, meaning that they have a specific molar ratio to the metal ions, whereas sequestrants do not.
Soils typically encountered on reusable medical devices
The soils found on devices to be cleaned may be organic, inorganic or both in nature. Organic soils may be comprised of muscle, skin, connective tissue, fat, grease, proteins (blood), carbohydrates, micro-organisms and other bodily fluids. Organic soils tend to be predominantly proteinaceous in nature. Inorganic soils may consist of rust, scale (hard water deposits), residues from cleaners and residues from medical solutions (iodine, saline, skin preparations). Combination (organic and inorganic) soils may originate from substances such as bone.
Medical device protection Rust (Fe2
O3 ) is a corrosion product
sometimes found on medical devices containing iron (which of course includes stainless steel). Depending upon its oxidation state, this corrosion can be reddish-brown through to black. Some rust can be easily wiped off (sometimes called flash rust), whereas pitting corrosion is referred to as persistent rust, and is very difficult to remove. Detergents can be formulated with corrosion inhibitors to prevent this corrosion. Other components can be formulated together collectively impart not only cleaning, but also allow: Wetting of the surface Sequestration Chelation Soil elevation and help to prevent redeposition
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Choosing a high performance detergent
There is much more to a detergent than just a surfactant in aqueous solution, and the correct formulation can make a significant difference to enhance its cleaning efficacy. Additional components may be added that will enhance the suitability of the product for its intended purpose. Selecting the best detergent clearly requires an appreciation of all of these attributes.
Through a process of scientific studies and washer validation, a number of high level conclusions can be drawn: Alkaline-based detergents are generally better at rendering surfaces non-infectious than enzymatic detergents
Alkaline and enzymatic detergents have been demonstrated to be effective at inactivating transmissible spongiform encephalopathies (TSEs) such as prion proteins
The precise formulation may have more of a bearing on cleaning performance than whether the detergent is classified as alkaline or enzymatic
The suitability of a given detergent formulation will depend upon the washer-disinfector cycle parameters, the particular washer-disinfector used, and the water quality at the point of use
Detergents should be formulated to be low foaming and have the ability to defoam
Have high performance against difficult soils such as proteins
Protect surgical instruments from corrosion and staining
Reduce maintenance costs by minimising pump cavitation
All detergent formulation components should be biodegradable, non-toxic to aquatic life and free from environment-damaging chemicals
Provided in minimal packaging by concentrating the formulation.
CSJ AUGUST 2019
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