Low-Temperature Sterilization Methods

Not all medical devices can withstand the high temperatures and moisture of steam sterilization. Low-temperature sterilization methods were developed for heat-sensitive and moisture-sensitive devices, including flexible endoscopes, powered instruments, cameras, and fiber-optic cables.

---

1. Ethylene Oxide (EtO) Sterilization

EtO is a gas that kills microorganisms by alkylation — it disrupts DNA and proteins, preventing organisms from reproducing.

Parameters:

Advantages:

• Effective on virtually all materials (including plastics, rubber, electronics)
• Penetrates packaging and complex device geometries
• Well-established efficacy data

Disadvantages:

• Toxic and carcinogenic — strict OSHA monitoring required (PEL: 1 ppm TWA, 5 ppm STEL)
• Long total cycle time (exposure + aeration = 12-24+ hours)
• Aeration required to remove toxic EtO residuals from devices before patient use
• Flammable in pure form (mixed with CO₂ or HCFC to reduce flammability)
• Environmental concerns — regulated as an air pollutant
• Cannot be used for items needed urgently due to long cycle times

Biological Indicator:

• Bacillus atrophaeus (formerly B. subtilis var. niger) spores

---

2. Hydrogen Peroxide Gas Plasma (STERRAD)

Uses hydrogen peroxide vapor that is energized into a plasma state by radiofrequency energy. The plasma breaks down the hydrogen peroxide into water and oxygen — leaving no toxic residuals.

Parameters:

Advantages:

• Fast cycles — some as short as 24 minutes
• No toxic residuals — items are ready to use immediately after cycle
• No aeration needed
• Low temperature — safe for most heat-sensitive devices
• Environmentally friendly — byproducts are water and oxygen

Limitations:

• Cannot process cellulose materials (paper, cotton, linen, cardboard) — cellulose absorbs hydrogen peroxide
• Cannot process liquids or powders
• Lumen restrictions — some narrow or long lumens may not be compatible (check device IFU and STERRAD compatibility charts)
• Cannot use woven textile wraps (cellulose) — must use Tyvek or polypropylene packaging
• Higher per-cycle cost than steam sterilization

Biological Indicator:

• Geobacillus stearothermophilus spores (same as steam, but different formulation)

---

3. Vaporized Hydrogen Peroxide (VHP / V-PRO)

Similar to gas plasma but uses vaporized (non-plasma) hydrogen peroxide:

Key Differences from Gas Plasma:

• No plasma phase — uses hydrogen peroxide in vapor phase throughout
• Different cycle parameters and lumen capabilities
• Some models have enhanced lumen penetration with special accessories

Parameters:

Limitations:

• Same cellulose restriction as gas plasma
• Cannot process liquids or powders
• Specific lumen length and diameter restrictions per manufacturer

Biological Indicator:

• Geobacillus stearothermophilus spores

---

4. Ozone Sterilization

Uses ozone (O₃) generated from oxygen and water:

Parameters:

Advantages:

• Generated from oxygen and water — no toxic chemical storage
• Low temperature
• No aeration needed
• Relatively gentle on instruments

Limitations:

• Limited material compatibility data compared to steam and EtO
• Some materials (natural rubber, certain plastics) may be damaged
• Longer cycle times than hydrogen peroxide methods
• Not as widely adopted in U.S. healthcare facilities

Biological Indicator:

• Geobacillus stearothermophilus spores

---

5. Peracetic Acid (Liquid Chemical Sterilization)

Peracetic acid (PAA) systems immerse devices in a heated, dilute peracetic acid solution:

Parameters:

Key Characteristic:

• Items are processed as immersible, point-of-use devices
• Items cannot be stored after processing — they must be used immediately
• Typically used for flexible endoscopes and other immersible devices
• Not compatible with non-immersible devices

---

Comparison Chart