Washer-Disinfectors: Cleaning Theory

Achieving reliable cleaning results requires a delicate balance of four factors: action, temperature, concentration, and time. Each element plays a critical role in the overall performance of an automated washer-disinfector. Understanding and managing these factors is essential for thorough cleaning of surgical instruments and medical devices.

 

Definitions

 

Action – The physical contact of both mechanical cleaning and chemistry on the object being cleaned. In an automated washer this is achieved by a combination of the wash pump, rotating wash arms, and spray nozzles.  Action is influenced by things like the chemical makeup of the detergent, washer spray pattern, and water pressure. Action may sometimes also be referred to as mechanics.

Temperature – The amount of thermal energy added to the wash cycle. It is important to achieve a temperature that optimizes the effect of any detergents used in the cleaning process. An automated washer uses electric or steam heaters to control temperature.

Concentration – The amount chemical solution (detergent) added to a wash cycle relative to the volume of water. Higher amount of detergent can reduce the need for increased action and time but may be less cost effective. Concentration may sometimes also be referred to as chemistry. A washer’s dosing system controls the level of concentration used in a wash cycle. 

Time – The duration that an object is exposed to the other three factors.

 

Factors Affecting Wash Action

 

• Water Volume – Enough water to reach all surfaces of the objects being washed and to build up adequate pump pressure. Belimed washers use a dynamic filling concept to ensure there is adequate water for washing but not a wasteful amount.
• Loading Pattern – Improper washer loading techniques can result in inadequate washing action. Washers must be properly loaded to ensure adequate cleaning.
• Water Pressure – The higher the water pressure is the better the cleaning however, pressure should not be so high that objects are being moved around by the water pressure.
• Spray Pattern – The wash arm design and speed of rotation impact the washing action.
• Mechanical Components and Design – Pump design, piping/tubing diameters, rack design, chamber size, etc. all effect cleaning action.
• Excessive Foaming – Impacts the performance of the wash pump. Foam cannot be efficiently pumped and will result in decreased cleaning action. Always make sure instruments are properly rinsed before placing them into an automated washer.

 

Temperature Considerations

 

• Material Stability - Some instruments may be damaged or deformed by excessive temperatures. Ensure the instrument’s Instructions for Use (IFU) are consulted before washing any instrument.
• Type of Soil – Blood is rich in proteins which will coagulate at elevated temperatures. If this type of coagulation occurs it will be extremely difficult to clean the instrument. Always pre-rinse instruments with cool water prior to washing.
• Detergent Chemistry – Alkaline cleaners tend to be more effective the higher the temperature is. Enzymatic cleaners will denature at high temperatures and begin to lose their effectiveness. No matter what detergent is being used, always follow the detergent’s IFU.

 

Concentration

 

• Detergent Chemistry – Cleaning agents are designed to be used at certain concentrations. If too much is used foaming will occur inside of the wash chamber. Excessive foam can interfere with the performance of the wash pump and cause reduced cleaning action. Too little detergent will result in inadequate cleaning. Always follow the detergent’s IFU’s.

 

The longer action, temperature, and chemicals act on an instrument, the better the cleaning result.

One factor may be substituted for another. For example, if less detergent is used it can be compensated for by increasing a cycle’s run time (illustrated below).

 

 

Key Take-Aways

 

• A successful wash cycle requires the proper balance of four cleaning factors: action, temperature, concentration, and time.
• Improper washer loading techniques can result in inadequate washing action. Washers must be properly loaded to ensure adequate cleaning.
• Ensure instruments are properly rinsed before placing them inside a washer. Excessive foaming will reduce cleaning efficiency and possibly cause failed cycles.
• Always reference the detergent’s IFU’s for the correct temperature and dosing quantities.
• Cleaning factors may be optimized but must always stay in balance with one another.