Sterilization, Disinfection, and Instrument Processing
This domain follows an instrument from the dirty field back to the sterile shelf. The exam tests the Spaulding classification, why cleaning always precedes any microbicidal step, the parameters that make each sterilization method work, and how a load is monitored and released. Expect stems that hinge on a single number or on the difference between disinfection and sterilization.
Spaulding classification
Critical items enter sterile tissue or the vascular system and require sterilization (instruments, implants, needles). Semicritical items contact mucous membranes or nonintact skin and require high-level disinfection at minimum (endoscopes, laryngoscope blades, respiratory equipment). Noncritical items contact intact skin and need low-level disinfection (blood pressure cuffs, stretchers, bed rails).
Cleaning first, always
Organic soil - blood, fat, saline - protects organisms and inactivates chemical germicides, so no method works over debris. Instruments are transported moist, kept from drying, and cleaned with an enzymatic detergent, then rinsed, inspected, lubricated, and packaged with a chemical indicator inside and out.
Methods and parameters
Steam gravity displacement runs near 121°C (250°F) at 15 psi for roughly 15–30 minutes; the prevacuum cycle runs near 132–134°C (270°F) for 3–4 minutes. Ethylene oxide works at low temperature for heat-sensitive items and requires aeration to remove toxic residue. Hydrogen peroxide plasma and peracetic acid are low-temperature alternatives. Glutaraldehyde 2.4% gives high-level disinfection in about 20 minutes at 20–25°C but needs roughly 10 hours for sterilization - a frequent exam distractor.
Monitoring and release
Mechanical monitoring reads gauges and charts; chemical indicators confirm exposure to process parameters but never prove sterility; biological indicators are the release authority. Steam uses Geobacillus stearothermophilus; ethylene oxide and dry heat use Bacillus atrophaeus. Every load is documented and traceable to the patient.
Worked example
A steam load's biological indicator incubates positive. Correct response: quarantine and recall every item from that load - even those already distributed - notify the surgeon and infection prevention, take the sterilizer out of service, review the cycle record, and repeat the BI before returning the unit to use. A positive chemical indicator alone would merely mean the item did not go through the cycle.
Traps that cost marks
Confusing high-level disinfection with sterilization; treating a chemical indicator as proof of sterility; forgetting EO aeration; mixing up which biological indicator belongs to which method.