Instrument Milk: Surgical Instruments Require Proper Maintenance

Instrument Milk: Surgical Instruments Require Proper Maintenance

By Nancy Chobin, RN, AAS, ACSP, CSPM

Q: During a recent survey, we were questioned by the surveyor if we treated our instruments with a lubricant. We responded that we only use “instrument milk” when the instrument is stiff. The surveyor said we should be using one. Can you advise on this?

A: Most surgical instrument manufacturers recommend regular lubrication of surgical instruments to keep them in good working order. Instruments that require lubrication should be treated with the type of lubricant that is recommended by the instrument manufacturer and that is compatible with the subsequent sterilization process. Water-soluble lubricants are compatible with steam sterilization (AORN, 2016).

The lubricant should always be prepared according to the lubricant manufacturer’s instructions.

The recommended quality of the water used to dilute the lubricant varies with the lubricant manufacturer, but critical water (distilled, deionized, or reverse osmosis [RO]) is usually recommended. AAMI (ST-79; 2017) states, “Instrument lubricants should be specifically designed for their intended use and compatible with the processing method being used. The lubricant manufacturer should provide evidence to support material compatibility and biocompatibility (e.g., lack of cytotoxicity) of the lubricant for its intended use (e.g., following sterilization). Lubricants should be used according to the device manufacturer’s instructions.”

“Diluting with tap water might leave crystals that could interfere with sterilization” (Bartnett, 2008). “Instruments should be cleaned before the lubricant is applied. Cleaning, particularly ultrasonic cleaning, removes lubricants from instruments. Lubricants decrease friction between working surfaces.” (Bartnett, 2008)

“When carefully selected, lubricants can do much more than reduce friction and wear; they can lengthen the useful life of an instrument. Lubricants for medical equipment and invasive surgeries have obvious health and safety requirements. For example, hygiene and environmental regulations require lubricants to be discrete, non-toxic and effective.” (Bartnett, 2008)

The lubricant should be water-soluble and should be recommended for use on instruments. An oil- or grease-based lubricant should never be used, because it will interfere with the sterilization process. Steam, for example, cannot penetrate oil or grease; only water-based surgical lubricants are steam-penetrable. Using an inappropriate lubricant can thus lead to inadequate sterilization of surgical instruments and, ultimately, adversely affect surgical outcomes. Sometimes the lubricant is referred to as “instrument milk” because most of these products are white in color. Some lubricants are available pre-mixed, whereas others are concentrated and must be diluted.

It is important to read the lubricant manufacturer’s IFU to determine the quality and quantity of water that should be used for dilution. “If the lubricant is over-diluted, it will not be effective. Conversely, if a lubricant is too concentrated or too heavily applied, it will result in slippery instruments that are difficult to handle. Devices may also be mistakenly identified as being wet after sterilization if they have concentrated lubricant on them.” (Bartnett, 2008).
Because most instrument lubricants are not microbicidal, they might have a use-by date (expiration date) to limit the use of the product (microorganisms can grow in the solution and then be deposited on the instruments). The lubricant manufacturer’s instructions for use and expiration dating should always be followed.

Instruments can be lubricated manually, or the lubricant can be applied mechanically in an instrument washer. When lubrication is performed manually, the instrument milk bath should be located in the preparation and packaging area, not in the decontamination area where it could become contaminated. For manual lubrication, the instruments should be opened and dipped into the lubricant solution, not allowed to soak. If too much lubrication is used, it can build up and cause instrument joints to stick. The instruments should be placed in the lubricant solution for the length of time specified by the lubricant manufacturer and then allowed to air dry. The lubricant should not be wiped or rinsed off. The container should be washed and thoroughly rinsed before it is reused. For convenience, some automated washers have a preprogrammed lubrication cycle to facilitate routine lubrication. (Bartnett, 2008)

When a container is used to lubricate instruments manually, the lid must be kept on the container and the container must be marked with the lubricant’s expiration date (if one is specified by the lubricant manufacturer).

“It is important to see the lubrication step not merely as an add-on but as a proactive step in the instrument care process that provides a film of protection against wear from metal-on-metal friction of moving joints. If carefully selected, lubricants can lengthen the life of surgical instruments by:
1. “Reducing wear and friction
2. “Preventing staining and rusting during sterilization and storage
3. “Contributing to ease of use
4. “Preventing corrosion due to friction” (Bartnett, 2008)

In summary, do not assume that all instruments should be lubricated. It is important to verify that the instrument manufacturer recommends lubrication; some implant manufacturers, for example, do not recommend that the screws or plates be placed in instrument milk. It is also important to verify in the IFU that the lubricant is compatible with the sterilization process to be used. For example, not all instrument lubricants are compatible with low-temperature sterilization methods. Some lubricants will react with the EO and cause the instrument to “freeze.” Some manufacturers do not recommend lubrication of ophthalmic instruments. This is why reading the lubricant and instrument manufacturer’s IFU is critical.

Nancy Chobin, RN, AAS, ACSP, CSPM, is a sterile processing consultant and educator.

ANSI/AAMI:  ST79:2017. “Comprehensive Guide to Steam Sterilization and Sterility Assurance in Healthcare Facilities.”

Association of periOperative Registered Nurses. Guideline for cleaning and care of surgical instruments and powered equipment. In: Guideline for Perioperative Practice. Denver: AORN, 2016.

Bartnett CA. The optimal selection and use of surgical instrument lubricants. Healthcare Purchasing News, May 2008. Available at:

Chobin N. The Basics of Flexible Endoscope Reprocessing. 2nd ed. Lebanon, N.J.: Sterile Processing University, LLC, 2016.

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