Sterilization vs. Disinfection
Sterilization is the complete destruction or elimination of all forms of microbial life, including bacterial spores. Disinfection reduces the number of viable organisms but does not reliably kill spores. Every item entering a sterile body cavity must be sterilized, not merely disinfected.
Steam Sterilization (Autoclave)
| Parameter | Detail |
|---|
| Mechanism | Saturated steam under pressure denatures microbial proteins |
| Gravity displacement cycle | 250-254°F (121-123°C), approximately 30 minutes |
| Prevacuum (dynamic air removal) cycle | 270-276°F (132-135°C), approximately 4 minutes |
| Best for | Heat- and moisture-stable metal instruments, textiles |
| Not suitable for | Heat-sensitive plastics, electronics, powered equipment, lensed instruments (unless designated steam-safe) |
Ethylene Oxide (EtO) Gas Sterilization
| Parameter | Detail |
|---|
| Mechanism | Alkylation of microbial DNA/protein, preventing replication |
| Cycle time | Several hours for exposure, plus mandatory aeration (up to 8-12 hours or longer) |
| Best for | Heat- and moisture-sensitive items - plastics, electronics, powered equipment, endoscopes |
| Safety concerns | EtO is flammable, toxic, and a known carcinogen; requires aeration before handling and strict engineering controls |
Hydrogen Peroxide Gas Plasma (e.g., Sterrad)
| Parameter | Detail |
|---|
| Mechanism | Vaporized hydrogen peroxide generates free radicals that disrupt microbial cell function |
| Cycle time | Approximately 28-75 minutes depending on system and load |
| Best for | Heat- and moisture-sensitive instruments; low-temperature alternative to EtO |
| Limitations | Cannot process items with cellulose (paper, linen) or long, narrow lumens without a booster/diffusion accessory; no toxic residue or aeration required |
Dry Heat Sterilization
| Parameter | Detail |
|---|
| Mechanism | Oxidation of microbial cells through prolonged heat exposure |
| Cycle | 320°F (160°C) for 2 hours, or higher temperatures for shorter times |
| Best for | Anhydrous oils, powders, and sharp instruments that steam could dull or corrode |
Liquid Chemical Sterilants (High-Level Disinfection Alternative)
Peracetic acid and glutaraldehyde-based systems can achieve sterilization for immersible, heat-sensitive items such as flexible endoscopes, but items must be used immediately since they cannot be wrapped and stored sterile after processing.
Verifying Sterilization
| Indicator Type | Purpose |
|---|
| Mechanical (physical) monitors | Sterilizer gauges, printouts of time, temperature, and pressure for each cycle |
| Chemical indicators (Class 1-6) | Color or state change confirming exposure to sterilizing conditions; placed inside and outside each pack |
| Biological indicators (BIs) | Contain live spores (Geobacillus stearothermophilus for steam, Bacillus atrophaeus for EtO); the definitive test of sterility - run at minimum weekly and with every load containing an implant |
Key Exam Points
- An implant load requires a biological indicator with a rapid-readout result before the implant is released for use, whenever feasible.
- Flash (immediate-use) steam sterilization is reserved for emergencies, not for convenience or lack of instrument inventory.
- Event-related shelf life, not time-related shelf life, is the current standard - a sterile package remains sterile until the integrity of the packaging is compromised.
- Manufacturer's Instructions for Use (IFU) govern the specific validated cycle for each instrument and tray.