IDI - Irish Decontamination Institute

Recommendations by the Quality Task Group
[9] Cleaning and Disinfection in the Ultrasonic Bath (Part 2)

In ultrasonic baths different energy fields are generated depending on the position of the ultrasonic transducers (figure 1). The specified level for filling the baths must absolutely be observed as this affects the energy input. Moreover, ultrasonic shadowing occurs depending on the quantity, shape and position of the sterile items and permit a more or less beneficial effect. In principle, inserts or mesh trays whose meshes are not too narrow should be chosen. These must be placed on the positioning rollers of the unit and under no circumstances directly on the floor of the bath. The mesh trays should not be overfilled. Nor should silicone mats be used as they impede the ultrasonic effect. The load should be chosen such that the mesh trays can be placed directly without reloading into the washer-disinfectors immediately after ultrasonic treatment. Jointed instruments should be opened and complex instruments may need to be dismantled, while observing the manufacturer's instructions. To achieve an optimal cleaning result, these LOADING INSTRUCTIONS must be strictly observed.

The effect of disinfectants, and also the cleansing ultrasonic effect, depends on the extent of contamination and is adversely affected by extensive contamination. Therefore the baths should be regularly renewed. The FREQUENCY of renewal depends on how often the bath is used and on the degree of contamination. Baths with visible contamination should be renewed possibly several times each day. Otherwise, daily renewal is recommended.

Normal drinking water can be used for the ultrasonic bath. But some manufacturers recommend the use of softened water or demineralised water. It has been demonstrated in practice that preference should be given to SOFTENED WATER.

Fig. 1:	Field distribution and intensities of the cavitation field at one level of a commercial ultrasonic bath, showing the thermistor sensor (Rudolf Reichl, NMI Naturwissenschaftliches und Medizinisches Institut at Tübingen University)

Experience from the practical setting:

• Mesh trays with highly contaminated instruments should always be pre-cleaned in the ultrasonic bath as otherwise they will not be properly cleaned in the washer-disinfector.
• Once a week all trays with instruments are subject to pre-treatment in the ultrasonic bath.
• Instruments are preferably processed in a tunnel washer with integrated ultrasonic bath.
• Hardened protein residues and rust are removed by using in the ultrasonic bath a general cleaning agent containing phosphoric acid. This also reinforces the passive layer and curtails susceptibility to rust. But only hardened instruments may be treated thus.
• Biopsy forceps are in principle cleaned in the ultrasonic bath and then rinsed, dried, packed and sterilised.
• Gynaecological instruments, e.g. specula, are often not cleaned properly. They must generally undergo pre-treatment.
• Microinstruments that can only be cleaned manually are cleaned in the ultrasonic bath.