2.4 Automated Cleaning Methods

Automated cleaning equipment provides standardized, reproducible, and validatable results that are more consistent than manual cleaning alone, and it reduces the technician's contact with contaminated items. It does not fully replace manual cleaning — it supplements it. Heavily soiled or complex instruments are still pre-cleaned by hand before automated processing.

Washer-Disinfectors (WDs)

The primary automated cleaning equipment in most CS departments. A typical cycle runs in sequence:

1. Cold pre-wash / flush — removes gross soil and blood before heat is applied (heat first would coagulate protein).
2. Enzymatic or detergent wash — chemistry applied at the specified temperature.
3. Rinse — one or more rinses remove detergent.
4. Thermal disinfection — water heated to roughly 180-195°F (82-90°C) for a set time.
5. Drying — heated forced-air phase on many models.

Thermal disinfection at these temperatures provides intermediate-level disinfection so items are safe to handle on the clean side, but items that must be sterile still require sterilization afterward. The killing power of moist heat is often expressed as the A0 value, a measure that combines time and temperature; an A0 of 600 is a common minimum target for a washer-disinfector cycle.

Loading a washer-disinfector

• Open all hinged instruments so water reaches box locks.
• Position concave items (cups, basins) on edge or face-down so they drain and do not trap water.
• Do not overload; water and detergent must reach every surface and spray arms must spin freely.
• Separate dissimilar metals (e.g., stainless and aluminum) to prevent galvanic corrosion.
• Use the correct racks and lumen-irrigation adapters for the device.

Ultrasonic Cleaners

Ultrasonic cleaners use high-frequency sound waves (20,000-40,000 Hz / 20-40 kHz) to create microscopic bubbles in the solution. This process is cavitation:

• Sound waves create alternating high- and low-pressure zones.
• In low-pressure zones, tiny bubbles form.
• In high-pressure zones, the bubbles implode against the instrument, generating intense localized energy.
• The implosions dislodge soil from crevices, hinges, serrations, and lumens that brushes cannot reach.

Key points:

• Ultrasonic cleaning is a cleaning process only — it does not disinfect.
• Instruments must be fully submerged; the lid is closed to limit aerosols.
• Never put your hands in an operating unit — cavitation damages tissue.
• Degas fresh solution: run the empty unit for the recommended time to drive out dissolved air, which otherwise cushions and blocks cavitation.
• Change solution at set intervals or when visibly soiled.
• Do not process chrome-plated instruments — cavitation can separate the plating.
• Separate dissimilar metals here too, to avoid electrolysis/ion transfer.

Cart Washers and Washer-Sterilizers

Cart washers are large drive-through or roll-in machines for case carts, transport carts, and big containers; load so spray reaches all surfaces. Washer-sterilizers combine washing and steam in one older-technology cycle; they are being phased out because items finish wet (weakening the sterile barrier) and the cycle is hard to validate — a separate washer-disinfector plus a dedicated sterilizer gives better results.

Verification and Monitoring

Automated equipment must be monitored to prove it works:

The foil test for an ultrasonic cleaner is a practical check: a sheet of thin aluminum foil suspended in the tank should show uniform pitting/perforation after a short cycle, confirming cavitation reaches all areas. Water quality is now governed by ANSI/AAMI ST108 (which superseded TIR34); poor-quality water leaves spots, scale, and stains and can corrode instruments.

Loading Best Practices Summary

Worked Scenario and Traps

Scenario: Cannulated instruments come out of the washer with dried blood inside the lumens. The likely causes are that the lumen-irrigation adapters were not connected, the tray was overloaded so spray could not penetrate, or POU flushing was skipped. The fix is to attach the correct flush adapters, reduce the load, and pre-clean lumens manually.

Common traps: assuming an ultrasonic cleaner disinfects (it does not); forgetting to degas; running chrome-plated or fiber-optic items in the ultrasonic unit; relying on the washer for items the IFU says must be cleaned manually; and skipping daily cleaning-verification checks.

Washer-disinfectors and ultrasonic cleaners are only as reliable as their preventive-maintenance program. Spray arms clog with debris and lint, jets become misaligned, gaskets crack, and detergent dosing pumps drift out of calibration; any of these silently degrades cleaning while the cycle still appears to "pass." That is why routine cleaning-verification testing matters more than the visual appearance of a finished load. Document every cycle's temperature and parameters, log maintenance, and tag and remove from service any machine that fails verification until it is repaired and re-tested.

Manufacturers' Instructions for Use remain the final authority: the IFU specifies which cycle, which racks, which adapters, and whether a given device may be processed automatically at all — when an IFU conflicts with habit, the IFU wins.