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♨️ Sterilization Methods

Sterilization destroys all forms of microbial life, including bacterial spores. Choosing the right method depends on the device material and the manufacturer IFU.

⏱ About 10 minute read

What sterilization means

Sterilization is the complete destruction or elimination of all forms of microbial life, including highly resistant bacterial spores. It is an absolute term — an item is either sterile or it is not. This differs from disinfection, which reduces microorganisms but may not kill all spores.

The method selected must be validated for the device and is dictated by the manufacturer's instructions for use (IFU), which always take precedence.

Steam sterilization (moist heat)

Steam under pressure is the most common, economical, and preferred method for heat- and moisture-stable items. It works by denaturing and coagulating cell proteins.

🔑 Common steam parameters

  • Gravity displacement: 250°F (121°C) for ~30 min, or 270°F (132°C) for ~15 min.
  • Pre-vacuum (dynamic air removal): 270–275°F (132–135°C) for ~3–4 min, plus drying.

Four factors must all be present: time, temperature, moisture (steam), and direct contact.

Immediate Use Steam Sterilization (IUSS)

Formerly called "flash" sterilization, IUSS is used only when there is insufficient time to process by conventional means (e.g., a dropped, single instrument urgently needed). It is not intended for routine processing, implants (except documented emergencies), or to compensate for inadequate instrument inventory.

Low-temperature sterilization

Heat- and moisture-sensitive devices (plastics, electronics, many endoscopes) require low-temperature methods:

  • Hydrogen peroxide gas plasma / vaporized H₂O₂ — fast cycles, leaves no toxic residue; cannot process cellulose (paper, linen) or long/narrow lumens beyond stated limits.
  • Ethylene oxide (EO/EtO) — highly penetrating, excellent for complex lumens, but toxic, flammable, and requires lengthy aeration to remove residuals. EO is a known carcinogen, so exposure monitoring is required.
  • Ozone and peracetic acid (liquid chemical, point-of-use for immersible devices) are additional options.
⚠️ Low-temperature methods have strict lumen length and diameter limits. Always verify the device against the sterilizer IFU.

Monitoring sterilization

Every load must be monitored using a combination of indicators:

  • Physical/mechanical monitors — printouts and gauges of time, temperature, and pressure.
  • Chemical indicators (CIs) — change color when exposed to process conditions. External CIs (e.g., autoclave tape) confirm a pack was processed; internal CIs confirm the sterilant penetrated.
  • Biological indicators (BIs) — contain highly resistant spores (Geobacillus stearothermophilus for steam/H₂O₂; Bacillus atrophaeus for EO/dry heat). A BI is the only monitor that directly proves microbial kill.

🔑 Bowie-Dick test

A pre-vacuum steam sterilizer must pass a daily Bowie-Dick air-removal test in an otherwise empty chamber before the first processed load.

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