Key Takeaways
- Sterilization kills ALL microorganisms including spores; disinfection kills most but not all organisms
- Steam sterilization (autoclave) is the most common, most reliable, and most cost-effective method
- Standard gravity autoclave settings: 250°F (121°C) at 15-17 psi for 15-30 minutes (wrapped items)
- Prevacuum (pre-vac) autoclave: 270°F (132°C) at 27 psi for 4 minutes (wrapped items)
- Flash/immediate-use sterilization: 270°F for 3 minutes (unwrapped) — used only in emergencies, not routine
- Ethylene oxide (ETO) gas sterilization is used for heat-sensitive and moisture-sensitive items
- Hydrogen peroxide plasma (Sterrad) sterilizes heat-sensitive items faster than ETO with no toxic residue
- Biological indicators (BIs) are the gold standard for verifying sterilization — Geobacillus stearothermophilus for steam, Bacillus atrophaeus for ETO
Last updated: February 2026
Equipment Sterilization & Maintenance
Sterilization and disinfection are fundamental to preventing surgical site infections. The CST exam tests this topic extensively (17 scored questions, 11.3% of the exam).
Decontamination Hierarchy: Spaulding Classification
| Level | Definition | Method | Items |
|---|---|---|---|
| Critical | Contact sterile tissue or vascular system | Sterilization | Surgical instruments, implants |
| Semi-critical | Contact mucous membranes or non-intact skin | High-level disinfection (HLD) | Endoscopes, laryngoscope blades |
| Non-critical | Contact intact skin only | Low-level disinfection | Blood pressure cuffs, OR furniture |
Sterilization Methods
1. Steam Sterilization (Autoclave) — Most Common
| Parameter | Gravity Cycle | Prevacuum (Pre-vac) Cycle |
|---|---|---|
| Temperature | 250°F (121°C) | 270°F (132°C) |
| Pressure | 15-17 psi | 27 psi |
| Time (wrapped) | 15-30 minutes | 3-4 minutes |
| Time (unwrapped) | 10 minutes | 3 minutes |
| How it works | Steam displaces air by gravity | Vacuum pump removes air before steam enters |
| Advantage | Simpler, reliable | Faster, better steam penetration |
| Limitation | Slower; less efficient air removal | More expensive equipment |
Flash/Immediate-Use Steam Sterilization (IUSS):
- 270°F for 3 minutes (gravity) or 3 minutes (prevacuum), unwrapped
- Used only when an instrument is needed urgently and no sterile replacement is available
- NOT acceptable for routine sterilization or implants
- Must be used immediately after cycle — cannot be stored
2. Ethylene Oxide (ETO) Gas
| Parameter | Details |
|---|---|
| Temperature | 85-145°F (29-63°C) |
| Time | 1-6 hours exposure + 8-12 hours aeration |
| Use | Heat-sensitive and moisture-sensitive items |
| Advantage | Penetrates packaging and lumens; effective at low temperatures |
| Disadvantage | Toxic, carcinogenic, flammable; requires long aeration time; OSHA-regulated |
3. Hydrogen Peroxide Plasma (Sterrad)
| Parameter | Details |
|---|---|
| Temperature | 104-131°F (40-55°C) |
| Time | 28-75 minutes depending on cycle |
| Use | Heat-sensitive items (endoscopes, power tools, cameras) |
| Advantage | Fast, no toxic residue, no aeration needed |
| Disadvantage | Cannot sterilize cellulose (paper, linen, cotton) or liquids; limited lumen length |
4. Other Methods
| Method | Use |
|---|---|
| Glutaraldehyde (Cidex) | High-level disinfection (not sterilization unless 10-hour soak) |
| Peracetic acid (Steris) | Liquid chemical sterilization for immersible items; used immediately |
| Dry heat | Items damaged by moisture (powders, oils, petroleum products); 320°F for 1-2 hours |
| Ionizing radiation | Industrial sterilization of disposable items (syringes, sutures, gloves) |
Sterilization Monitoring
| Indicator Type | What It Tests | Examples |
|---|---|---|
| Mechanical (physical) | Machine parameters (temp, pressure, time) | Autoclave printout/chart recorder |
| Chemical | Exposure to sterilization conditions | External indicator tape, internal CI strips (Class 1-6) |
| Biological (BI) | Actual killing of spores — GOLD STANDARD | Spore tests read at 24-48 hrs (or rapid 1-3 hrs) |
Biological Indicator Organisms
| Sterilization Method | BI Organism |
|---|---|
| Steam (autoclave) | Geobacillus stearothermophilus |
| ETO (ethylene oxide) | Bacillus atrophaeus (formerly B. subtilis) |
| Hydrogen peroxide plasma | Geobacillus stearothermophilus |
| Dry heat | Bacillus atrophaeus |
Instrument Processing Workflow
- Point-of-use treatment: Keep instruments moist; spray with enzymatic foam at the point of use
- Transport: In closed, labeled containers to SPD (prevent aerosolization)
- Decontamination: Manual or automated washing (ultrasonic cleaner, washer-decontaminator)
- Inspection: Check instruments for cleanliness, function, sharpness, alignment
- Assembly: Assemble instrument trays per count sheet; add internal chemical indicator
- Packaging: Wrap in sequential double-layer wrap or rigid container; apply external indicator tape
- Sterilization: Load autoclave correctly (allow steam circulation), run cycle
- Storage: Store in clean, dry, limited-access area; check expiration before use
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Test Your Knowledge
What is the standard temperature and exposure time for a gravity steam sterilization cycle with wrapped instruments?
A
B
C
D
Test Your Knowledge
Which biological indicator organism is used to verify steam (autoclave) sterilization?
A
B
C
D
Test Your Knowledge
Flash (immediate-use) sterilization should be used:
A
B
C
D
Test Your Knowledge
Which sterilization method is appropriate for heat-sensitive items like endoscopes but CANNOT be used for cellulose products (paper, linen)?
A
B
C
D
Test Your KnowledgeOrdering
Place the instrument processing steps in the correct order:
Arrange the items in the correct order
1
Sterilization (autoclave)
2
Decontamination (washing)
3
Point-of-use treatment (enzymatic spray)
4
Inspection and assembly
5
Packaging and wrapping
Test Your KnowledgeMulti-Select
Which of the following are disadvantages of ethylene oxide (ETO) sterilization? (Select all that apply)
Select all that apply
Toxic and carcinogenic
Cannot sterilize heat-sensitive items
Requires long aeration time (8-12 hours)
Flammable
Very expensive equipment