ity to dissolve substances such as fats, whether solid or liq-uid. Cleaning solutions containing a detergent or nonaqueoussolvent are more effective for the removal of fats and other oils.

The addition of enzymes that break down proteins enablesthe cleaning solution to remove blood and other gross soilfrom instruments (Barnes, 2002). Enzymes generally breakdown large molecules into smaller water-soluble ones thatcan be rinsed away after cleaning. The enzymes used in manydetergents work best at a neutral pH. Because these enzymesdo not rely on, and indeed may be inactivated by, particu-larly high or low pH, they have the added advantage of notpromoting instrument corrosion. Because enzymes them-selves are macromolecules that can lose their effectivenessover time, when using enzymatic detergents, freshly madesolutions are a must (Natural Toxins Research Center, 2004).Another excellent reason for changing the enzymatic watersolution each time is to prevent cross-contamination (Nelsonet al., 2003).

Surfactants are another important component of thesecleaning solutions. Surfactants lower surface tension, enablingdroplets of solution to disperse more easily and more quicklyand completely coat a surface (Perkins, 1998). Surfactantsalso emulsify oily soils, keeping them dispersed and suspendedso they can be more readily rinsed away. Many cleaning solu-tions contain two or more surfactants.

The Truth and Consequences ofEnzymatic DetergentsBettyann Hutchisson, BSN, RN, MSOT

Candy LeBlanc, BSN, RN

Enzymatic detergents are widely used to clean gastrointestinal endoscopes before high-level disinfection.

Although proper use of enzymatic detergents may appear straightforward, common misuses include failure

to dilute the enzymatic detergent, overdilution of enzymatic detergent, use of expired enzymatic detergent,

inadequate exposure time, and failure to rinse the enzymatic detergent from the instrument being cleaned.

Each type of misuse has its own rationale. In these studies, the authors show by high-performance liquid

chromatography that the type of enzymatic detergent and the dilution and rinsing of enzymatic detergents

affect the amount of residual high-level disinfectant (ortho-phthalaldehyde) left on test segments of flexible

endoscope insertion tubes. The authors also qualitatively demonstrate that proteinaceous material, which is

stained a dark color by ortho-phthalaldehyde (OPA), remains on colonoscopes that have been cleaned with

improperly diluted or rinsed enzymatic detergents. These findings emphasize the importance of diluting and

using enzymatic detergents exactly as directed by their manufacturers to reduce bioburden and residual

amounts of high-level disinfectant on flexible endoscopes.

Received February 1, 2005; accepted March 24, 2005.About the authors: Bettyann Hutchisson, BSN, RN, MSOT, is Clinical Education Consultant; and Candy LeBlanc, BSN, RN, is Manager, ProductConsulting, Advanced Sterilization Products, Irvine, California.Author correspondence to: Bettyann Hutchisson, BSN, RN, MSOT, 2255 Eldridge Parkway, No. 1712, Houston, TX 77077 (e-mail:bhutchis@aspus.jnj.com).

The goal of cleaning endoscopic devices beforesterilization or high-level disinfection is to reducethe amount of bioburden on the instrumentbeing cleaned (Society of Gastroenterology

Nurses and Associates [SGNA], 2000, 2004). To make appro-priate decisions to facilitate the removal of visible and non-visible soil, staff members must have a sound knowledge ofthe items they are cleaning and the tools available to accom-plish this cleaning. Such knowledge leads to an enhancedeffectiveness of the high-level disinfection or sterilization pro-tocol being followed (Lind, 2003).

Background

An ideal cleaning solution should be inexpensive, readilyavailable, and not harmful to the device being cleaned or theperson cleaning it (Lind, 2003). Tap water is only margin-ally successful in cleaning instruments because of its inabil-

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Molecules of surfactant can be electrically charged or neu-tral. Anionic surfactants are negatively charged in solution(Perkins, 1998). They have excellent cleaning properties andcreate a lot of suds. Laundry, dishwashing, and personal clean-ing products are examples of household anionic detergents.

Nonionic detergents do not form ions in solution. Theyclean most surfaces well and generally are effective even inhard water. Nonionic detergents are low sudsing. Automaticdishwasher detergent and laundry detergent are examples ofhousehold nonionic detergents.

For all the components in cleaning solutions to work well,they must be in the correct concentrations (Wasek, 2003);therefore, accurate dilution of cleaning solutions accordingto manufacturers’ instructions is important. Usually, 0.5 or1.0 ounce of enzymatic detergent is used per gallon of water.

Although proper use of enzymatic detergents is straight-forward, detergents also can be used improperly (Chobin &Erickson, 2003; Wasek, 2003;). Common misuses include fail-ure to dilute the enzymatic detergent, overdilution of deter-gent, use of expired enzymatic detergent, inadequate exposuretime, and failure to adequately rinse the enzymatic detergentfrom the instrument being cleaned. Each type of misuse hasits own rationale, including:

• Use of undiluted enzymatic detergent commonly occurs inthe precleaning stage, when the undiluted detergent is suc-tioned into the endoscope and may or may not be followedby water. The false rationale is that the higher concentrationof enzymatic detergent is more effective in reducing biobur-den before cleaning.

• Overdilution commonly occurs during cleaning in settingsin which a “recipe card” of volumes of water and enzymaticdetergent established for proper dilution of the detergent isnot posted as a visual reminder. The false rationale is thatindividual technicians have different preferences of volumesto be used and that volume is of no consequence because “alittle goes a long way.”

• Use of expired enzymatic detergent occurs commonly wherelarge inventories of detergent are in storage. The incorrectbelief that the enzymatic detergent is only soap, so the expi-ration date is inconsequential, is behind this particularmisuse.

• Inadequate exposure time commonly occurs when the tech-nician cleaning endoscopes is quick and efficient but doesnot allow for adequate contact time as stated on the label,particularly in the channels of endoscopes. The incorrectbelief behind such inadequate exposure is that for properprocessing, mere exposure of an endoscope to enzymaticdetergent would suffice.

• Lack of rinsing is common when using an automatic en-doscope reprocessor (AER). The rationale is that becausethe AER rinses the instrument before high-level disin-fection, manual rinsing to remove enzymatic detergent isunnecessary.

Cleaning of endoscopes goes in tandem with high-level dis-infection. An aqueous solution of ortho-phthalaldehyde(OPA) is used widely as a high-level disinfectant duringendoscope reprocessing because of its excellent materialscompatibility, safety, and ease of use. Because OPA stainsproteinaceous material, residual bioburden appears blackafter exposure to OPA. This characteristic of OPA, but notof other high-level disinfectants, can be used to qualitativelyassess the presence of residual proteinaceous material in

endoscopes after reprocessing. Ortho-phthalaldehyde itselfcan be quantitatively assessed by analytical chemistry tech-niques. We report the results of two experiments designed tolook at the types of enzymatic detergents and the effect ofcleaning conditions on the amount of OPA and the presenceof stainable proteinaceous material recovered after high leveldisinfection of colonoscopes.

Methods

Quantitative Assessment of Residual OPATwelve 10- to 12-cm segments of flexible endoscope inser-tion tube (Pentax Medical Company, Montvale, NJ) wereexposed to bioburden similar to that which would be pres-ent in a clinical setting and were then allowed to air dry.After drying, the segments were divided into three groupsof four, labeled “Nonionic 1 (expired),” “Anionic,” and“Nonionic 2” based on the detergent type to be used. Eachgroup was then manually cleaned with the designated testdetergent under one of four use conditions:

1. One ounce of detergent per 4 gallons of water, followed bywater rinses

2. One ounce of detergent per 1 gallon of water, followed bywater rinses

3. One ounce of detergent per 1 gallon of water, with nowater rinse

4. Undiluted detergent, followed by water rinses

The manufacturers’ instructions for both test detergentsspecified that 1 ounce of detergent should be used per gal-lon of water.

After being cleaned, the segments were again air dried andthen exposed to 0.55% OPA solution (Advanced SterilizationProducts, Irvine, CA) at room temperature (20°C) for 12 min-utes. After being exposed to the OPA, the test samples wererinsed with sterile water according to the manufacturer’sdirections for use. The rinsed segments were then placedindividually in glass test tubes containing 100 mL of 0.87%physiological saline. These test tubes were then placed in a37°C incubator. After 24 hours, an aliquot from each testtube was analyzed for OPA residual by high performanceliquid chromatography (HILC Waters 2690 with UV Detec-tor, Waters Corporation, Milford, MA).

Qualitative Assessment of ResidualsFive Pentax colonoscopes received bioburden during colono-scopies performed at Presbyterian Hospital of Dallas (Dallas,TX). The colonoscopes were precleaned in the procedureroom by wiping the exterior of the insertion tube with prop-erly diluted enzymatic detergent and suctioning the detergentsolution through the endoscope channels. The colonoscopeswere then manually cleaned with the designated test deter-gents as follows:

• Endoscope 1: 1 ounce of Nonionic Enzymatic Detergent1 per 1 gallon of water, followed by water rinses

• Endoscope 2: 1 ounce of Nonionic Enzymatic Detergent2 per 1 gallon of water, followed by water rinses

• Endoscope 3: 4 ounces of Nonionic Enzymatic Detergent2 per 1 gallon of water, followed by water rinses

• Endoscope 4: 1 ounce of Nonionic Enzymatic Detergent1 per 1 gallon of water, with no rinse

• Endoscope 5: Undiluted Nonionic Enzymatic Detergent 1,followed by water rinses

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For both detergents, the manufacturers’ instructions directedthat 1 ounce of detergent be used per 1 gallon of water.

The colonoscopes were then processed in PresbyterianHospital of Dallas’ AER using OPA solution as the high-leveldisinfectant. The scopes did not receive a final air purge oralcohol flush at the end of the reprocessing cycle. They werehung vertically to dry. An absorbent, white cloth was placedon the floor of the endoscope cabinet to catch effluent drip-ping from the distal tips of the endoscopes.

Results

Residual OPAFigure 1 shows the amounts of OPA remaining on disinfec-ted endoscope segments previously cleaned with enzyme-containing detergents under various conditions. Under allconditions, cleaning with anionic detergents was associatedwith at least twice as much residual OPA as cleaning withnonionic detergent.

Residual Proteinaceous MaterialOrtho-phthalaldehyde reacts with residual bioburden andother proteinaceous material to form dark stains. The photo-graphs in Figure 2(A–E) show stains on absorbent cloth thatcaught fluid dripping from hanging colonoscopes as theyair dried. The colonoscopes were cleaned as indicated andthen underwent high-level disinfection with OPA solution.The amount of staining varied, depending on the cleaningconditions.

Discussion

This study demonstrates the importance of using nonionicsurfactant enzymatic detergents only as specified by theirmanufacturers. The cleaning conditions used in the studywere selected because anecdotes of similarly improper use—and the false rationale behind such use—are well known(Chobin & Erickson, 2003; Wasek, 2003). Our study illus-trates the rationale behind the use of improperly dilutedenzymatic detergents is erroneous, and such improper useresults in serious, negative consequences.

Residual OPAThe low-sudsing character of the nonionic detergent made iteasy to rinse. In contrast, the anionic surfactant detergentwas high-sudsing, making it difficult to rinse at all dilutions.This difference in ability to rinse provided the most plausi-ble explanation for the lower OPA residual seen with non-ionic detergent compared with anionic detergent for all dilu-tions examined. Overall, OPA residuals were at least twiceas high after washing with anionic detergent as after non-ionic detergent washing. For dilutions of fresh (not expired)anionic enzymatic detergent, higher concentrations of deter-gent and detergent not rinsed according to the manufacturer’sdirections generally led to higher OPA residuals. Residuallevels of OPA should be of concern to instrument-processingtechnicians and supervisors because they indicate improperprocessing of scopes and the potential for the negative con-sequences of trapped bioburden.

Proteinaceous ResidueNo staining of proteinaceous material by OPA was observedafter high level disinfection of endoscopes that had beencleaned with properly diluted nonionic detergent and thenrinsed with water. In contrast, staining was observed withthe endoscope that had been cleaned with properly diluteddetergent, but not rinsed. Significant staining also was ob-served with endoscopes cleaned with underdiluted and un-diluted nonionic detergent and then rinsed as usual. Theseresults provided a visual illustration of the importance ofusing detergent as directed by the manufacturer.

The residual material that stained the white cloth was aresult of liquid that dripped from the endoscope because nofinal air or alcohol flush was performed at the end of thereprocessing cycle. This demonstrates that in improperlycleaned endoscopes, small amounts of such residual materialmight be left on interior and exterior surfaces of endoscopesas they dry. This visual illustration of residual material stainedby OPA is a message to technicians and supervisors that theyshould evaluate current cleaning procedures to ensure suc-cessful high-level disinfection and complete removal of anybioburden on instruments, ensuring patient safety. In addi-tion, the possibility of build-up over time could raise concernsabout the effectiveness of future cleaning processes afterrepeated improper cleaning, as well as the negative effect onthe optimal functioning and lifetime of the endoscope itself.

Improving the Process to Enable BetterUse of Enzymatic DetergentOur study underscores the importance of using nonionicenzymatic detergents precisely as directed by their manufac-turers. Implementation of two simple, practical changes could

F I G U R E 1 . Bioburden was dried onto 10- to 12-cm segments offlexible endoscope tubing. Tubing was washed with expired nonionicenzymatic detergent (Nonionic 1 [expired]), anionic enzymatic detergent (Anionic), or a second, fresh nonionic enzymatic detergent(Nonionic 2). These detergents were diluted 1 oz to 4 gallons of water(blue bars), 1 oz to 1 gallon water (red and yellow bars), or not diluted(green bars). After washing, all but three samples were rinsed withwater (yellow bars show no rinse). Tubing segments were air dried and exposed to 0.55% ortho-phthalaldehyde solution for 12 minutes at20°C, rinsed, and air dried. They were then incubated in 0.87% salineat 37°C for 24 hours, after which the saline was analyzed for the presence of ortho-phthalaldehyde by high performance liquid chromatography.

Ortho-phthalaldehyde (OPA) Remaining onFlexible Endoscope Tubing

0.000

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

Nonionic #1 EXPIRED Anionic Nonionic #2

Detergent

mg

of O

PA

/ pe

r gr

am o

f pol

yure

than

etu

bing

mat

eria

l

1 oz/4 gal

1 oz/gal

No rinse

Undiluted

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F I G U R E 2 . Photos show the white cloth positioned below endo-scopes manually cleaned with nonionic enzymatic detergents andwater rinsed (unless indicated otherwise) as follows: (A) detergent 1properly diluted (1 oz/gallon water), (B) detergent 2 properly diluted (1 oz/gallon), (C) detergent 2 underdiluted (4 oz/gallon water), (D) detergent 1 properly diluted (1 oz/gallon) but not rinsed before high level disinfection, and (E) detergent 1 undiluted.

A

C

D

E

B

help with precleaning and cleaning in many endoscopy suites.For precleaning, every morning an appropriately dilutedgallon of nonexpired enzymatic solution could be placed ineach procedure room. The properly diluted enzymatic solu-tion is then poured from the gallon container into a smallercontainer for immediate suctioning of solution through thechannels of the endoscope directly after use, before bioburdenhas a chance to dry in the channels.

In the cleaning room, a permanent marker or piece of tapecould be used to mark in the sink the amount of water nec-

essary to submerge an endoscope. Then a “recipe card” couldbe posted specifying how many pumps of nonexpired enzy-matic detergent should be added to that amount of water(Figure 3). Fresh water should be used for every endo-scope. To achieve a reliable reduction of bioburden, theendoscope should remain submerged in the detergent, andthe channels should be in contact with the solution for theamount of time specified on the detergent’s label. The endo-scope should then be rinsed with fresh water to remove theenzymatic detergent.

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Conclusions

Although it is true that when used correctly, enzymatic clean-ers are very effective in removing soil and organic matter, italso is true there are serious negative consequences associ-ated with enzymatic misuse. In these studies, nonionic deter-gents are associated with much less residual OPA after high-level disinfection than are anionic detergents. We believe thisdifference is attributable to the low-sudsing and easy-to-rinsecharacteristics of the nonionic detergents compared with thehigh-foaming nature of the anionic detergents. Furthermore,if nonionic detergent is not rinsed after cleaning, or if it isunderdiluted or undiluted for cleaning, OPA-stained liquidwill drip from the distal tip of the cleaned, high-level disin-fected endoscopes. This will be evidenced by staining of theabsorbent cloth, indicating bioburden remains on the endo-

scope after cleaning, and this residual material may interferewith successful high-level disinfection. These findings are evi-dence that to achieve the best possible outcomes, nonionicenzymatic detergents used for cleaning gastrointestinal endo-scopes should be fresh and properly diluted and used as spec-ified by the manufacturer.

AcknowledgmentThe authors thank Harriett Chan-Myers, Tina Yu, JoshHagerman, and Joseph Ascenzi, PhD, for their assistance.

ReferencesBarnes, R. (2002). Enzymes. Communique, May/June, 8–9.Chobin, N., & Erickson, S. E. (2003). Endoscopy and infec-

tion control. Infection Control Today, April, 14–20.Lind, N. (2003). Common sense cleaning. Communique,

November/December, 6–7.Perkins, W. S. (1998). Surfactants: A primer. America’s Tex-

tiles International. Retrieved July 29, 2004, from http://www.p2pays.org/ref/03/02960.pdf

Position Statement: Multi-society guideline for reprocessingflexible gastrointestinal endoscopes (2003). Gastroin-testinal Endoscopy, 58(1), 1–8.

Rutala, W. A. & Weber, D. J. (2004). Reprocessing endo-scopes: United States perspective. Journal of HospitalInfection, 56, 527–539.

Society of Gastroenterology Nurses and Associates, Inc.(SGNA). (2000). Standards of infection control in repro-cessing of flexible gastrointestinal endoscopes. Gastro-enterology Nursing, 23(4), 180–187.

Society of Gastroenterology Nurses and Associates, Inc.(SGNA). (2004). Guideline for the use of high-level dis-infectants and sterilants for reprocessing of flexible gas-trointestinal endoscopes. Gastroenterology Nursing, 27(4),198–206.

Wasek, S. (2003). 11 Common endoscope handling mistakes.Outpatient Surgery, June, 52–59.

F I G U R E 3 . An enzymatic detergent recipe card should beposted as a reminder of the correct amount of water and enzymaticdetergent to be used while cleaning scopes.

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