Liquid chemical sterilization, often called “cold sterilization,” processes medical instruments that cannot withstand the high temperatures of traditional steam sterilization. This method involves completely submerging heat-sensitive devices in a chemical solution to eliminate microorganisms. The duration the instrument remains submerged, known as the contact time, is the most significant factor determining success. The chemical must contact every surface for a precise amount of time to ensure efficacy. This required submersion time changes based on the intended outcome and the specific chemical used.
Sterilization Versus High-Level Disinfection
The required submersion time changes depending on whether the goal is sterilization or high-level disinfection (HLD). Sterilization is a validated process intended to render a product free of all viable microorganisms, including highly resistant bacterial spores. Devices classified as “critical items,” which penetrate sterile tissues, require true sterilization.
HLD eliminates all vegetative bacteria, fungi, viruses, and mycobacteria, but it may not reliably kill large numbers of bacterial spores. HLD is reserved for “semicritical items,” such as flexible endoscopes, which contact mucous membranes. The time necessary to achieve HLD is considerably shorter, often ranging from 10 to 45 minutes, depending on the chemical agent. Achieving sterilization, which requires killing the most resilient spores, demands a significantly longer exposure time, often measured in hours.
Variables Influencing Required Submersion Time
The manufacturer-specified contact time is a minimum standard easily compromised by environmental and procedural factors. Temperature plays a significant role, as the activity of most chemical germicides increases with warmth. However, excessive heat can cause the chemical to degrade, weakening its sanitizing power. Processing must occur within the specific temperature range designated by the product’s instructions.
The concentration of the chemical solution is another major variable; any dilution can render the process ineffective. Instruments not completely dried before submersion introduce water, lowering the active chemical concentration below its minimum effective concentration (MEC). Furthermore, the presence of organic matter, known as bioburden, directly interferes with the chemical’s ability to kill microbes. If debris remains on an instrument after cleaning, the germicide will be neutralized and cannot reach the pathogens.
Contact Time Requirements for Common Chemical Agents
The specific submersion time depends entirely on the chemical agent chosen and the desired level of microbial kill.
Glutaraldehyde
Glutaraldehyde, typically used at 2.0% or greater, has historically been a common agent for both HLD and sterilization. For high-level disinfection, instruments must be submerged for 20 to 90 minutes at room temperature (generally 20°C to 25°C). Achieving true sterilization requires extending the contact time to a minimum of 10 hours at the same temperature range.
Ortho-phthalaldehyde (OPA)
OPA, often used at 0.55%, is a popular alternative primarily for its rapid high-level disinfection capabilities. OPA can achieve HLD in as little as 12 minutes at 20°C. When used in automated endoscope reprocessors at 25°C, this time can drop to around 5 minutes. OPA is generally not cleared for a sterilization claim in the United States, limiting its use primarily to the HLD of semicritical devices.
Hydrogen Peroxide and Peracetic Acid
Formulations based on hydrogen peroxide (e.g., 7.5% concentration) and peracetic acid offer both HLD and sterilization capabilities. High-level disinfection requires a 30-minute submersion at 20°C. To reach the sterilization endpoint, instruments must be soaked for 6 hours at 20°C. Healthcare facilities must strictly adhere to these specific manufacturer minimums, as any reduction in time or concentration compromises the safety of the reprocessed instrument.
Essential Steps Preceding and Following Submersion
The submersion time is only one phase of a multi-step protocol required to properly prepare a medical instrument.
Pre-Submersion Steps
Before the chemical bath, instruments must undergo mandatory pre-cleaning to remove all organic and inorganic soil. This process involves the manual scrubbing of instruments, particularly hinged or complex pieces, followed by a thorough rinse to eliminate residual detergent. The instrument must then be completely dried. Any moisture will dilute the chemical solution and reduce its effectiveness.
Post-Submersion Steps
After the required contact time is complete, the instruments must be removed and rinsed multiple times to eliminate the toxic chemical residue left on the surfaces. This rinsing step must be performed using sterile water to prevent recontamination of the now disinfected or sterilized instrument. Following the final rinse, the instrument must be dried immediately and thoroughly. Since instruments processed by liquid chemicals cannot be wrapped during the submersion phase, they must be used as soon as possible, or stored under proper aseptic conditions to maintain the achieved level of cleanliness.