6.2 Reprocessing Steps & High-Level Disinfection (HLD)

6.2 Reprocessing Steps & High-Level Disinfection (HLD)

Quick Answer: Reprocessing reusable medical devices—especially flexible endoscopes—via High-Level Disinfection (HLD) is a strictly regulated, multi-step sequential workflow: Point-of-use pre-cleaning, Leak testing, Manual enzymatic cleaning, Rinsing, HLD application (using OPA, Glutaraldehyde, or Peracetic acid), Final rinsing, Alcohol flush & forced-air drying, and Vertical storage. High-level disinfectant solutions must undergo Minimum Effective Concentration (MEC) testing prior to every load to verify active microbicidal concentration.

Flexible endoscopes (e.g., colonoscopes, gastroscopes, bronchoscopes, duodenoscopes, transesophageal echocardiogram [TEE] probes) present unique infection prevention challenges. They are complex semi-critical instruments featuring long, narrow internal lumens, flexible elevator channels, control valves, and optical components that cannot tolerate high-temperature steam autoclaving.

Failure at any single link in the reprocessing chain—such as delayed point-of-use pre-cleaning, missed leak tests, inadequate lumen brushing, expired Minimum Effective Concentration (MEC) test strips, or humid horizontal storage—can lead to microbial survival, biofilm formation, and widespread patient exposure to bloodborne pathogens or multidrug-resistant organisms (MDROs).

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The 7-Step Sequential HLD Reprocessing Workflow

The CDC, SGNA (Society of Gastroenterology Nurses and Associates), AAMI (ANSI/AAMI ST91), and APIC mandate a standardized 7-step sequence for reprocessing semi-critical devices:

1. Point-of-Use Pre-Cleaning (Procedure Room):

   • Performed immediately upon removal of the scope from the patient, while still connected to the light source and suction pump.
   • Wipe the exterior insertion tube with an enzymatic detergent solution using a lint-free sponge or cloth. Aspirate/flush enzymatic detergent solution continuously through internal suction and biopsy channels until clear.
   • Purpose: Prevents blood, mucus, glycoprotein secretions, and bioburden from drying on external surfaces and inside internal channels. Dried bioburden forms a protective matrix (biofilm) that shields microorganisms from chemical disinfectants.

2. Leak Testing (Decontamination Room):

   • Performed in the dedicated decontamination room prior to submersing the endoscope in cleaning liquid.
   • Attach the mechanical or automated leak tester to the scope's electronic connector. Pressurize the inner chassis. Inspect the pressure gauge (dry leak test) and submerge the scope in clean water (wet leak test), flexing the distal tip in all directions while observing for continuous streams of air bubbles.
   • Purpose: Identifies microscopic tears, holes, or seal breakdowns in the outer sheath or internal channels. Fluids entering the inner chassis damage expensive electronics/optics and create un-cleanable internal reservoirs where bacteria like Pseudomonas can proliferate.

3. Manual Enzymatic Cleaning & Brushing:

   • Fully submerge the scope in a freshly prepared solution of multi-enzymatic detergent diluted according to manufacturer instructions for use (IFU) regarding water temperature and concentration. Thoroughly brush all accessible channels, ports, and elevator wire mechanisms using dedicated, single-use, channel-sized cleaning brushes until no visible debris remains.
   • Rule of Cleaning: “You cannot disinfect or sterilize an item that is not clean.” Chemical high-level disinfectants cannot penetrate thick layers of organic material or dried bioburden.

4. Rinse (Post-Cleaning):

   • Thoroughly rinse the scope exterior and flush all internal lumens with clean utility water to remove residual enzymatic detergent and loosened soil. Detergent residues can neutralize high-level disinfectant chemicals.

5. High-Level Disinfection (HLD Soak or AER):

   • Submerge the device in an FDA-cleared HLD solution for the exact contact time and temperature specified by the disinfectant manufacturer IFU, or process in an Automated Endoscope Reprocessor (AER).
   • Quality Check: Verify that the HLD chemical passes Minimum Effective Concentration (MEC) testing prior to starting the cycle.

6. Final Rinsing, Alcohol Flush, and Forced-Air Drying:

   • After HLD immersion, rinse the scope thoroughly with sterile water, bacteria-free water, or utility-filtered water (0.2-micron filter) to remove toxic chemical residues. Flush channels with 70-90% ethyl or isopropyl alcohol to act as a drying agent. Purge all channels with compressed medical-grade instrument air or HEPA-filtered air.
   • Purpose: Alcohol lowers surface tension and evaporates residual water droplets. Eliminating moisture is vital because residual water inside dark scope lumens allows opportunistic environmental water bacteria (e.g., Pseudomonas aeruginosa, Stenotrophomonas maltophilia, non-tuberculous mycobacteria) to multiply rapidly overnight.

7. Safe Storage and Vertical Hang Standards:

   • Store reprocessed endoscopes hanging vertically in a dedicated, secure, well-ventilated scope storage cabinet (preferably HEPA-filtered positive pressure cabinet). Removable parts (valves, caps) must be detached and stored alongside the scope.
   • Prohibitions: Scopes must never be stored coiled, laid flat in transport cases, or touching cabinet walls or floor.

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Comparison of Chemical Agents for High-Level Disinfection

Facilities select FDA-cleared liquid chemical germicides based on material compatibility, contact time, staff safety, and turn-around requirements.

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Minimum Effective Concentration (MEC) Quality Assurance

High-level disinfectants are reused over multiple days (e.g., 14-day or 28-day shelf life). However, repeated introduction of wet endoscopes dilutes the active chemical concentration over time.

• Mandatory MEC Testing: Prior to processing each load (or at minimum daily per facility protocol), staff must test the active chemical concentration using product-specific chemical test strips.
• MEC Threshold: For example, glutaraldehyde solutions typically have an MEC threshold of 1.5% to 2.0%, while OPA has an MEC threshold of 0.3%.
• Quality Control Rules for Test Strips:
  1. Test strips must be specific to the exact chemical formulation (do not use glutaraldehyde strips on OPA).
  2. Document open date and expiration date on the strip bottle (strips expire within 90–120 days of opening).
  3. Perform positive (diluted) and negative quality control testing on new strip bottles according to manufacturer instructions.
  4. If the test strip indicates the solution has fallen below the MEC (fails color indicator test), immediately discard the chemical solution, even if the 14-day or 28-day reuse life period has not expired.

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Duodenoscopes and Carbapenem-Resistant Enterobacteriaceae (CRE)

Duodenoscopes are specialized endoscopes used in Endoscopic Retrograde Cholangiopancreatography (ERCP) to diagnose and treat biliary and pancreatic duct disorders. They feature a complex, movable elevator mechanism at the distal tip designed to control accessories.

• Outbreak Risk: The sealed elevator channel and wire mechanism contain microscopic crevices that are extremely difficult to clean manually. Multiple global outbreaks of Carbapenem-Resistant Enterobacteriaceae (CRE) (e.g., Klebsiella pneumoniae, E. coli) were linked to contaminated duodenoscopes despite full compliance with standard HLD IFU.
• Enhanced CDC Supplemental Reprocessing Options: CDC recommends facilities performing ERCP adopt supplemental quality control measures:
  1. Double High-Level Disinfection (two full consecutive HLD cycles).
  2. Liquid chemical sterilization or Ethylene Oxide (EtO) gas sterilization.
  3. Microbiological culturing of duodenoscope channels to detect residual bacterial growth prior to release into clinical inventory.
  4. Transitioning to duodenoscopes with disposable or removable endcaps/distal components.