Decontamination
The correct pH for instrument reprocessing
Alan Abbatt offers an insight into ensuring the correct pH for detergents, to optimise the decontamination of surgical instruments. He considers why pH is important and examines the available guidance.
The correct pH-value for detergents formulated for decontaminating surgical instruments is a topic which attracts some debate between the manufacturers of the instruments themselves and the detergent manufacturers. Those involved with the production of stainless-steel surgical instruments would argue that there is a need to maintain pH neutral chemistry in order to preserve the lifespan and usefulness of the instruments, i.e. to prevent potential corrosion caused by acidic or alkaline chemical formulations. The alternative argument, and the one often presented by the manufacturers of the detergents, is that with careful research and development, formulations can be designed which are more effective than pH alkaline. The question is, who is correct?
Guidelines In the US, the CDC published its recommendation on Cleaning, A Guideline for Disinfection and Sterilization in Healthcare Facilities (2008). It states: “Ensure that the detergents or enzymatic cleaners selected [for cleaning of patient-care devices] are compatible with the metals and other materials used in medical instruments.” The guidance goes on to say that: “For instrument cleaning, a neutral or near- neutral pH detergent solution commonly is used because such solutions generally provide the best material compatibility profile and good soil removal… Neutral pH detergent solutions that contain enzymes are compatible with metals and other materials used in medical instruments and are the best choice for cleaning delicate medical instruments, especially flexible endoscopes. Alkaline-based cleaning agents are used for processing medical devices because they efficiently dissolve protein and fat residues; however, they can be corrosive.”1-4 The ‘Health T
echnical Memorandum (HTM) 01-01:
Management and decontamination of surgical instruments: Part D – Washer-disinfectors’ states: “For most applications, where compatible, alkaline detergents in the pH range 8.0–11.0 are preferred.”
Corrosion on a stainless steel surgical instrument magnified using an electron microscope
However, the HTM also details that: “The chemical additives used [in washer-disinfectors] should be compatible with the materials of which the load items are constructed and should not cause chemical or physical damage.”5 The European Society of Gastroenterology
and Endoscopy Nurses and Associates (ESGENA) also provide guidelines regarding the pH of detergents. On their website it details: “Detergents with alkaline boosters contain alkaline chemical substances forming a mild alkaline cleaner. Alkaline substances lift off soil and help to dissolve it in the cleaning solution.” These guidelines suggest that, even within the global sterile services community, there is an understanding as to the balance that needs to be struck for pH of detergents between the delicate cleaning required to prevent corrosion and the need to ensure the best possible decontamination of instruments and devices for the safety of patients.6
Why is pH important for decontamination of instruments? pH is a measure of how alkaline or acidic a substance is. pH has a range of 0-14. A pH greater than 7 means the substance is alkaline. A pH less than 7 means the substance is acidic. When the pH is around 7, that indicates that the substance is neutral. Certain substances associated with cleaning and disinfection will be alkaline in nature e.g., phosphate detergents (pH
9), ammonia, mild alkaline enzymatic detergents (pH 9.5 – 10.5) caustic detergents (pH 12) and bleach (pH 13).7 Alkaline cleaners are superior for dissolving soils that are based on fats, oils and proteins. They will break chemical and physical bonds of the contamination and make them easier to remove. This is an important consideration when reprocessing surgical instruments and other essential medical devices for re-use as they are often contaminated with substances such as blood which contain proteins, fats etc.
Cleaning action using alkaline detergents Alkaline cleaners work in a number of different ways including both chemical and physical actions. Saponification (as an example, for fat) is
where hydrolysis occurs between any ester substances found in the contaminants on a surgical instrument and the alkaline solution. As a result of this chemical reaction, triglycerides contained in the natural oils and fats are converted into glycerol and fatty acids. The latter react with the alkaline solution forming a soap like solution. Due to their good solubility in water, this soap is then easily removed by thorough rinsing. Detergency is the use of a detergent to
remove contaminants from a surface by infiltration, solubilising, suspending, dispersing, or emulsifying them. The detergency action is enabled by the presence of surfactants (detergents), that combine with impurities and dirt to make them more soluble or miscible. The surfactants in the detergent reduce the surface tension of the solution, improve the wettability, and help to infiltrate, emulsify or disperse non-dissolvable soiling, which can then be rinsed off by water. Energy is required to facilitate the removal of dirt from a surface. Therefore, the role of surfactants is to reduce the surface energy and subsequently the total energy required to achieve cleaning. Mechanical
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