Cleaning Challenges: Can Extended Soil Dry Times Be Reversed?

Abstract

Background: Cleaning is essential to ensuring the safe processing of reusable medical devices, and most manufacturers' instructions for use (IFUs) specify that clinical soil should not be allowed to dry on devices. If soil is allowed to dry, the cleaning challenge could be increased due to change in soil solubility. As a result, an additional step could be needed to reverse the chemical changes and return a device to a state where cleaning instructions are appropriate.

Methods: Using a solubility test method and surrogate medical devices, the experiment described in this article challenged eight remediation conditions to which a reusable medical device might be exposed if soil is dried on a device. These conditions included soaking with water or neutral pH, enzymatic, or alkaline detergent cleaning agents, as well as conditioning with an enzymatic humectant foam spray.

Results: The results demonstrated that only the alkaline cleaning agent was able to solubilize the extensively dried soil as effectively as the control, with a 15-minute soak being as effective as a 60-minute soak.

Discussion: Although opinions vary, the overall data demonstrating the risk and chemical changes that occur when soil dries on medical devices are limited. Further, in cases in which soil is allowed to dry on devices for an extended time outside of the guidance from leading practices and manufacturers' IFUs, what additional steps or processes may be necessary to ensure that cleaning can be effective?

Conclusion: This experiment demonstrated the effectiveness of a soaking step with an alkaline cleaning agent as an additional step if soil is dried on reusable medical devices, thus reversing the effect of an extended soil dry time.

This study was performed to assess the impact of an extended soak time with a variety of cleaning agent types, in order to determine their effectiveness at reversing the molecular changes on dried soil to ensure effective cleaning. Guidance documents (e.g., the Association of periOperative Registered Nurses' Guidelines for Perioperative Practice,¹ ANSI/AAMI ST79:2017²) highlight the increased challenge to the cleaning process if soils are allowed to dry for extended periods due to soil changes (e.g., coagulation).

In manufacturers' instructions for use (IFUs), point-of-use treatment typically is described as the first step in the safe and effective processing of reusable medical devices. This treatment usually is performed in the procedure room by healthcare personnel (e.g., perioperative staff) to include the removal of gross soil. Additional guidance is provided on keeping soil from drying on devices during subsequent transport to a designated processing area. Most IFUs also include the recommendation that users clean devices as soon as possible after use to minimize the potential for greater cleaning challenges.

The experiment described in this article challenged conditions in which point-of-use treatment is not performed or if the treatment is not effective at preventing soil from drying while waiting for decontamination to be performed.

Review of Literature

The cleaning of medical devices arguably is the most critical step in processing, as residual organic material left on devices can reduce the effectiveness of high-level disinfection and sterilization.² The chemical changes in clinical soils left to dry over time can lead to an increased patient risk of exposure to inadequately cleaned devices. Overall, scientific support for these risks is lacking, specifically regarding an understanding of the soil chemistry and effect of drying over extended periods of time in a variety of environmental conditions.

Although essential, water alone will not be effective for cleaning medical devices. It requires additional mechanisms of action (e.g., altering the surface tension between water and device surfaces). Water is best suited as an effective solvent in combination with a cleaning agent (e.g., detergent), which will be of particular importance in a scenario in which soil is allowed to dry.

Cleaning agent formulations can include a variety of chemicals, surfactants, and enzymes that are intended to be used to remove both organic and inorganic material from a substrate. These chemistries typically are water soluble and can come in a variety of preparations (e.g., liquid, aerosol, foam, wet wipes). They often are classified by their active chemistry (i.e., neutral pH, alkaline, acidic) or by the application that they are intended to be used during device processing (e.g., point of use, precleaning, ultrasonic, automated washer).

Cleaning chemistries typically contain surfactants designed to aid in the cleaning process. Surfactants reduce surface tension and increase the solubility of soils by detaching the soil from the surface of the device and emulsifying in solution, thereby facilitating removal. Surfactants can have different charges (e.g., anionic, nonionic, cationic, amphoteric), allowing them to have targeted attachment to soil components. Surfactants aid in removing the soil from the surface, as their hydrophobic tail bonds to the soil and their hydrophilic head keeps them in the water; this is the mechanism of emulsion that enables surfactants to emulsify soil.³

Neutral pH products (range pH 6–8) are a broad category of detergents that typically contain surfactants and other additives. The combination of these additives aids in the cleaning process, but these chemistries also are considered to be more compatible with device materials. Many of these cleaning chemistries also include enzymes that are designed to catalyze the breakdown of certain soil components and render them easier to remove from surfaces.⁴

Enzymatic cleaning chemistries include one or more enzymes in their formulations and can vary in pH range. Proteolytic enzymes break down long-chain–like molecules of proteins into shorter fragments (peptides) and, in some cases, eventually to their components (amino acids). Cleaning chemistries can also contain other enzymes such as lipases (enzymes active on lipids) and amylases (enzymes active on starches).⁵ Although these are all types of enzymes, it is understandable to deduce that their addition to a cleaning formulation may result in varying levels of effectiveness depending on the product and its use.

Mild alkaline detergents (pH 9–11) can aid in dissolving organic materials such as protein and fat residues.⁶ Alkaline detergents are excellent at removing most soil contaminants (e.g., proteins, lipids, carbohydrates). Alkaline solutions, depending on their formulation and use, can also be corrosive to certain materials and can dull and etch shiny metals (e.g., brass/copper, aluminum) or cause physical damage (e.g., corrosion, pitting, crazing) over time, thus shortening device life.⁷

Enzymes may also be added to alkaline detergents, and the potency of an enzymatic detergent can increase with pH, especially if an alkaline protease has been used in the formulation.⁸ However, if the formulation is too alkaline, it may cause enzymes to denature. In general, the higher the pH, the more aggressive the detergent can be on the surface of the device and in the removal of soil, but this will also be product specific.³

Research Design

Compared with other steps in a manual cleaning process (e.g., brushing, flushing), a soaking step is less burdensome. For the experiments described here, devices that had been soiled and dried for an extended period of time (72 hours) were soaked using a variety of cleaning chemistries. The percent solubility was measured before and after soaking to determine the effectiveness of the cleaning chemistries.

The following chemistry types were selected to determine whether an extended soaking time would increase the soil solubility once dried: critical water (as defined in AAMI TIR34:2014⁹), an alkaline enzymatic, a neutral pH detergent, three enzymatic detergents, and an enzymatic humectant foam spray.

Methods

Two surface types were evaluated within this experiment. A stainless steel coupon with dimensions of 25 × 50 × 6 mm and a surface area of 34 cm² was used to represent how device materials alone interact with test soil, and a stainless steel hemostatic clamp (VWR, Radnor, PA) with a surface area of 159 cm² was used to represent the interaction of test soil with complex device features (i.e., box hinge, mated surface). Henceforth, the hemostatic clamp will be referred to as the device feature.

Prior to testing, the coupons and device feature samples were cleaned by soaking in a cleaning agent (CIP 100; Steris, Mentor, OH) for 60 minutes and brushing to remove all residual soil until visibly clean. Coupons and device features then were rinsed under critical water for one minute and allowed to dry completely before presoiling weights were taken (~24 h).

The test soil chosen for the experiments was modified coagulated blood¹⁰ soil due to worst-case clinical exposure equivalency.¹¹ The test soil was prepared by blending 100 mL fresh egg yolk (Eggland's Best, Malvern, PA), 100 mL heparinized sheep's blood (Rockland, Royersford, PA), and 2 g dehydrated hog mucin (Sigma-Aldrich, St. Louis, MO). To reverse the anticoagulation properties for heparin, 0.05 g protamine sulphate (Thermo Scientific, Waltham, MA) was added to each 5 mL of soil, mixed, and used in the test system within 10 minutes.

The average protein concentration of modified coagulated blood was determined to be approximately 560,214 μg/mL using the BCA protein residual test and, therefore, was in excess of the maximum protein concentrations found on clinically used devices (117,758 μg/cm²).¹² The appropriate soil volume calculated for the coupon was 82,042 μg, delivered via a micro pipettor (Eppendorf, Hamburg, Germany) as 0.22 mL and smoothed across the coupon surface using the pipette tip to achieve a uniform thickness. The minimum soil volume (0.048 mL) was calculated for the device feature but did not provide sufficient coverage of the samples' complex features. To address this, the soil volume amount was increased to 0.15 mL and applied using a micro pipettor, delivering the soil to one surface and into the complex features (i.e., box hinge, mated surface, serrated clamp).

Coupons and device features were soiled and allowed to dry in an environmental chamber (Thermo Scientific) set to 22°C/71.6°F, 50% relative humidity, for 72 hours. A total of 33 samples were soaked in the cleaning agent for 60 minutes, for both coupons and device features. In addition, 33 coupons and device features were soaked for a shorter duration (15 min), in the alkaline enzymatic.

To evaluate an increased cleaning challenge for the device feature, the box hinge of the hemostatic clamp remained in the closed position for the chemistry soak, with the exception of the enzymatic humectant foam spray and the 15-minute alkaline enzymatic soak. This closed orientation was intended to simulate a worst-case situation in which attention to the device orientation may not be prioritized. In the closed position, the ability for the liquid to penetrate the soil and lift it into suspension would decrease. Because foam is not as likely to penetrate as liquid, the chemistry was applied with the box hinge in an open position for an appropriate challenge for these two scenarios.

In addition to the 72-hour dry control used to establish the most challenging drying time, a range of other controls with varying drying times were evaluated to assess at what point the soil solubility changed.

The solubility test was performed using gravimetric analysis to determine percent soil remaining. After soaking in the prescribed cleaning agent for the allotted time, the samples were placed into preheated (box hinge in open position for device feature), 45°C/113°F, extraction bag (Whirl-Pak, Madison, WI) filled with the appropriate volume of extraction fluid (150 mL critical water, as defined in AAMI TIR34:20149) for the coupons and 500 mL critical water for the device feature, allowing for complete submersion. The test system was validated with water as the solute to establish an acceptable challenge of soil adhesion. Extraction bags with samples were warmed in a water bath at 45°C/113°F for 60 minutes. Samples then were removed from the extraction bags slowly so as not to shear soil from sample surface. The samples were placed on a polypropylene drying sheet and allowed to dry completely before postextraction weight was recorded to determine percent soil retained.

Results

For the experiment, the soil solubility results for the various pretreatment methods were compared with the levels observed for the control dried samples (no soaking step), which demonstrated the point at which solubility decreased statistically on drying using a 95% confidence interval. The calculated inflection point for the coupon was 8 hours (3.6% soil remaining) and 48 hours for the device feature (10.9% soil remaining) (Figure 1).

Figure 1.

Effect of dry time and soil solubility (n = 12 control samples).

The results from the soaking studies are summarized in Table 1. Overall, the coupons demonstrated much greater soil remaining than the device feature tested and the formulations varied considerably. Soaking in water alone was not found to be very effective at reducing the percent soil remaining for either the coupons or device feature samples. Soaking in the neutral pH cleaning agent performed better than water alone, but the percent soil remaining did not reach the criteria set by the controls in increasing soil solubility.

Table 1.

Mean percent soil remaining, according to cleaning agent.

The performance of the enzymatic cleaning agents to increase soil solubility varied among formulations. Enzymatic 1 reduced the percent soil remaining to 8.11% and 24.86% for the coupons and device features, respectively, compared with enzymatic 2 (4.20% and 14.62%) and enzymatic 3 (0.11% and 12.22%). Although increased performance was observed compared with the water and neutral pH soaks, only one of the three enzymatic chemistries achieved the benchmark of the controls and only for the coupons. Enzymatic 2 reduced the soil retention to an amount that was statistically similar to the 8-hour controls (P = 0.838), and enzymatic 3 had a statistically significant decrease in the soil retention of the coupon samples. The device feature samples had a similar result compared with the 48-hour control, where the optimal enzymatic cleaning agent (enzymatic 3) demonstrated a 1.36% soil reduction compared with control (P = 0.239).

The impact of the application method was shown by comparing the liquid enzymatic cleaning agents with the enzymatic foam spray. The performance of the three neutral enzymatic cleaning agents showed greater statistical significance (P =0.001), with the enzymatic humectant foam spray demonstrating a reduced performance (34.14%) compared with even the worst-performing soak (enzymatic 1; 24.86%).

Coupon samples pretreated for 60 minutes with the alkaline enzymatic cleaning agent had a statistically significant decrease in soil retention of 2.93% (P = 0.008) compared with the 8-hour control. Device feature device samples under these same conditions showed a statistically similar percent soil retention to nonpretreated samples dried for 48 hours, decreasing the soil retention by 1.54% (P = 0.339). Both coupons and device features soaked in the alkaline cleaning agent for the short time of 15 minutes demonstrated the cleaning agent to be effective at reversing solubility changes similar to the 60-minute soak time, as long as the cleaning agent had access to device features (i.e., box hinge opened) (Figure 2).

Figure 2.

Percent soil remaining following exposure to cleaning agent (n=33 samples).

Discussion

The intent behind the point-of-use treatment step, as defined by medical device manufacturers' IFUs and leading practice guidance, is to appropriately condition the device as it awaits further processing. Instructions might entail complete removal of visible soil, conditioning the device to remain in a moist state, or a combination of the two. The actions to prevent soil from drying on a device are intended to keep the device in a condition in which the cleaning instructions validated by the manufacturer are the most effective. It is well established that dried soil is more difficult to remove from surfaces than wet soil. Understanding the efficiency of the variety of methods that can be recommended, including the use of cleaning detergents, to prevent or even reverse the impact of drying is important.

Cleaning chemistries demonstrate a wide variety of performance and should be used to appropriately address the soil chemistry remaining on the device regardless of the condition. Currently, no standards define the performance of cleaning agents used to clean reusable medical devices. Cleaning agent manufacturers do provide safety information regarding the use of chemistries, but information often is variable or lacking on other aspects to ensure their safe use on devices (e.g., residual toxicity levels, efficacy of soil removal).¹³ Understanding the chemistry as it applies to the situation in which it is being used therefore is important.

For example, with enzymatic cleaning agents, exposure time is a critical performance requirement. Although enzymes are designed to speed up a chemical reaction, the reaction may have a time requirement for optimal performance that is sometimes not achievable for routine device processing requirements (e.g., extended soak times³). As seen in the current study, although enzymatic cleaning agents can be effective at denaturing and solubilizing non–water-soluble proteins found in dried soil, they do not completely reverse the chemical changes and may require additional soaking time or manual cleaning steps to fully remove residual soil, especially when using on devices with complex features.

Alkaline cleaning agents use saponification and degradation mechanisms to remove residual soil, and the more alkaline the cleaning agent, the more aggressively it will clean the device. Alkaline detergents can be more efficient at removing most soil contaminants (e.g., proteins, lipids, carbohydrates) and have been demonstrated in the literature to be more reliable at removing the risks of prion contamination compared with enzymatic detergents when presoaked and rinsed.¹⁴ However, alkaline solutions can also cause damage to certain materials and thus may shorten the lifespan of devices. As a result, their use will be depend on the IFUs provided by medical device manufacturers. In general, the higher the pH, the more aggressive a cleaning agent will be on the surface of a device and at removing soil.³

It is not practical for medical device manufacturers to validate every possible cleaning agent that healthcare workers could use on a device. Device manufacturers are not required to list specific cleaning agents in their IFUs.¹⁵ Instead, they provide guidance and cleaning instructions to optimize the efficiency at which devices are processed, while balancing the human factors that may introduce risk. The cleaning validation typically is performed using cleaning agents with limited performance characteristics (e.g., neutral pH) on dried soil, which is representative of the testing done in the current study. In addition, mild alkaline cleaning agents often are used to process devices in end-of-life testing. By using the most aggressive cleaning agent to determine end of life and the least aggressive cleaning agent to validate the cleaning IFU, the healthcare facility is not required to use a specific cleaning agent during processing.

It would not be appropriate, and is not the intent of this discussion, to recommend against device processing leading practices, such as removal of gross soil at the point of use, not allowing devices to dry before cleaning, or manufacturer simulation of “extended dry time” during cleaning validation studies. Doing so would result in the inclusion of rigorous and excessive device processing steps in IFUs. In turn, this would overburden sterile processing department staff by increasing device processing time and heightening risk of noncompliance with IFUs.

By performing point-of-use treatment, devices stay in the condition validated by the manufacturer. However, within healthcare facilities, unexpected situations can result in extended drying of soil on devices. Therefore, the data collected in this study provide a level of confidence that steps can be taken to reverse the observed solubility changes and ensure efficient cleaning.

As demonstrated by the data, a 60-minute soak in a mild alkaline enzymatic cleaning agent was the most effective option for reversing soil drying when device features were not readily exposed. A 15-minute soak in a mild alkaline enzymatic cleaning agent was effective when all device features were exposed. Of important note, the specific device manufacturer's IFU must be consulted prior to initiating this additional soak in a mild alkaline enzymatic cleaning agent solution, in order to ensure compatibility with this type of cleaning agent.

Medical device manufacturers need to collaborate with device users (including sterile processing department staff) during the device design and clearance process to ensure the feasibility of using and processing devices. A theoretical framework has been developed that involved users of medical devices in the development process.¹⁶ It proposed two streams through which feedback should be solicited. The first stream involved the end user (patient) and professional user (physician). The evidence demonstrated that end users quickly discard devices that do not fulfill their expectations, even though both manufacturers and health professionals may consider that end user requirements have been met.

The same framework can be applied to device-processing technicians in healthcare facilities. Their input should be solicited for feedback on the device's design in terms of ease of processing, feasibility, and comprehension of IFUs. The study by Shah et al.¹⁶ demonstrated that end users may not continue to use a device if it does not meet their needs. The same could be said for the physician using a device on a patient or the device-processing technician who cannot clean, disinfect, or sterilize the device properly. All of these crucial aspects should be considered when designing a new medical device, performing validations, and developing IFUs.

Conclusion

Point-of-use treatment of reusable medical devices represents a critical step in device processing. This step provides assurance that the microbiological quality of a device is maintained from patient to patient. The execution of this step contributes to the safety factor that manufacturers consider when designing and validating cleaning processes for reusable medical devices.

This study demonstrated that potential remediations can be used to help solubilize soil in cases where soiled reusable devices are allowed to dry before being processed. However, this practice should be the exception and not the rule. The microbiological quality of a reusable medical device is the responsibility of everyone who comes in contact with it. Adherence to medical device manufacturers' IFUs is vital to maintaining the integrity of devices so that they may be used safely and effectively in patient care.