Because cleaning endpoints are not defined in AAMI TIR 30:2011, a major challenge faced by instrument manufacturers is determining how clean is clean. However, based on references provided in the compendium, a level for each of five markers, specifically protein, carbohydrate, hemoglobin, endotoxin, and bacterial spore reduction, can be determined (Table 1). These can be used as reasonable reference points.
Recent studies have determined the efficacy of cleaning processes for an assortment of reusable medical devices. The case studies summarized below provide examples of a supportable approach to demonstrate the effectiveness of a manual cleaning process of surgical instruments.
The purpose of the studies was to assess the efficacy of sponsor-proposed cleaning protocols (i.e., cleaning protocols proposed by manufacturers of reusable medical devices) based on the level of residual soil marker.
|Device Category||Soil Marker||Reference|
|Critical Orthopedic||Whole blood, serum, milk powder, and saline|||
|Semi-Critical Rectal and Esophageal||Peanut butter, evaporated milk, butter, flour, lard, dehydrated egg yolk, saline, printer’s ink, blood, Huckers artificial soil (fecal equivalent)|||
Study design, test methodology
The study, conducted at NAMSA laboratories, included critical and semi-critical devices; the devices under consideration were tested using soils that emulate biological soils that are appropriate for cleaning efficacy studies (Table 1). The cleaning procedure developed was based on the type of contamination expected on the device, design features, and the potential for the patient to come in contact with pathogens. For example, the appropriate test soils for verifying cleanliness of devices that enter the sterile body cavity (Table 2, Devices A and C through J) are different than those for devices that contact the mucosa and/or intact skin (Table 2, Device B).
The evaluations were conducted per a NAMSA protocol that is based on AAMI TIR30:2011 and AAMI TIR12:2010.3
Cleaning: Three soiled devices of each type were subjected to the sponsor-proposed cleaning procedure immediately after soiling. Each device was cleaned using freshly prepared cleaning solutions for a total of three or five cycles, depending on the device type. One common positive control (soiled but not cleaned) and one common negative control (not soiled and not cleaned) was included for each device type. After cleaning, each device was visually inspected for remaining soil. The volume and temperature of the cleaning solutions and rinse water were reported. While all device manufacturers specified the use of an enzymatic cleaner, the cleaning agent and process used was specific to the device manufacturer. Enzymatic solutions were prepared using manufacturers’ instructions for device soaking and then again for device sonication. The temperature of the cleaning solution was recorded prior to use.
Manual cleaning processes might employ sponges, soft bristle brushes, and/or pipe cleaners. Cleaning action might include wiping, scrubbing, and/or flushing depending on the protocol put forth by the device manufacturer. Mechanical cleaning utilized a commercial washer/disinfector.
|Test Article Device Category||Cleaning
|Benchmark (average)Protein Level(µg/cm2)||Test Article Device Protein Level(µg/cm2)||Benchmark (average)Hemoglobin Level(µg/cm2)||Test Article Device Hemoglobin Level(µg/cm2)|
|6.4||0.72||2.2||<2 .1=".1" td="td"> 2>|
|6.4||0.55||2.2||<2 .1=".1" td="td"> 2>|
|6.4||< 0.50||2.2||< 2.0|
|6.4||< 0.49||2.2||< 2.0|
Device Extraction: For each device type, three test devices, one positive control, and one negative control were extracted individually in bags filled with 12 mL of USP grade 0.9% sodium chloride (NaCl). Devices were extracted using 20 minutes of sonication followed by agitation by hand for 30 seconds. After each extraction, the solution was thoroughly mixed and decanted. The extraction procedure was repeated an additional two times (for a total of three extractions) using fresh solvent. The extracts were used for protein and hemoglobin analysis. Running tap water was used to rinse the devices for a period of three minutes prior to and after sonication. The volume of the rinse water ranged from 3,400 to 3,510 mL and the temperature of the rinse water ranged from 36 to 37 C.
Protein Analysis: A Pierce kit was utilized.4 A 150 μL aliquot of the 200 μg/mL, 20 μg/mL and 2.5 μg/mL bovine serum albumin (BSA) standards, the test extracts, and the blank solution were placed in individual wells in a 96-well plate; 150 μL of working reagent was added to each well. The plate was gently agitated by hand and incubated at 37 C for two hours. The plate was removed from the incubator and allowed to cool to room temperature. The plate was analyzed by a UV-visible spectrometer at 562 nm. The absorbance of the standards and test extracts were corrected for the blank solution absorbance; and a standard curve was generated to determine the protein concentration of the extracts.
Hemoglobin Analysis: An ASTM Method was utilized.5 A 2.0 mL aliquot of 10-3 M copper (II)-phthalocyanine complex solution and 2 mL of pH 2.0 buffer solution were placed in separate test tubes. A 5 mL aliquot of test extracts, hemoglobin standards, or a 0.9% NaCl control was added to each test tube and mixed. A 250 µL aliquot from each test tube was added to a 96-well plate. Using an eight-channel micropipette, 50 µL of 0.2 M solution of potassium peroxymonosulfate was added to each well to start the reaction. Since the reaction is time dependent, solutions were plated in rows of eight with the first four wells containing the hemoglobin standards and control, followed by test extracts.
After 0.2 M solution of potassium peroxymonosulfate was added to the last row in the plate, the plate sat at room temperature for 25 minutes.
The plate was then analyzed by a UV-visible spectrometer at 603 nm. Absorbance of the standards and test extracts were corrected for respective control absorbance and a standard curve was generated from each row on the plate to determine the hemoglobin concentration of the extracts.
Conversion: Units of µg/mL were converted to µg/cm2 by multiplying times the volume of extraction fluid used for each device (mL) and dividing by the device surface area (cm2).
No debris was observed during inspection of the cleaned devices. Results are summarized in Table 2, page 21.
As indicated, on a review of published data2 for various types of reusable devices, after device cleaning, the average levels of the two soil markers under consideration were:
• Protein: < 6.4 µg/cm2
• Hemoglobin: < 2.2 µg/cm2
As additional studies are performed and more data becomes available, these benchmark levels will become more definitive.
In all but one instance, the proposed cleaning methods evaluated utilizing protein and hemoglobin analysis met the acceptance criteria (the benchmark, average level).
Device C exceeded the average residue level for hemoglobin. It should be noted that the device in question is of a fairly complex design and would present greater inherent cleaning challenges. The method of cleaning was revised and the repeat testing (product G) showed a marked improvement.
Each device manufacturer must set testing and acceptance criteria that are appropriate to the configuration, materials of construction, and end-use requirements of each specific device under consideration. The rationale for testing and the rationale for acceptance criteria must be carefully considered and documented for the device in question.
1. Kanegsberg B, Kanegsberg E, Broad J. Update: Guidance for Cleaning Validation of Reusable Medical Devices, Controlled Environments. 2012:July/August;34-35.
2. AAMI TIR30:2011. A compendium of processes, materials, test methods, and acceptance criteria for cleaning reusable medical devices.
3. AAMI TIR12:2010. Designing, testing, and labeling reusable medical devices for reprocessing in health care facilities: A guide for medical device manufacturers.
4. Pierce Micro BCA Protein Assay Kit (Thermo Scientific).
5. ASTM F 756-08:2008. Standard Practice for Assessment of Hemolytic Properties of Materials.