Process

Hydrogen peroxide plasma sterilization uses low temperature, low moisture and gas plasma. Gas plasma is defined as a fourth state of matter consisting of clouds of ions, neutrons and electrons created by the application of an electric or magnetic field.

The sterilization procedure is divided into five phases:

• A vacuum phase, where the chamber is evacuated to around 0.1 – 0.3 mbar
• An injection phase, where liquid peroxide is injected, evaporating the Aquarius H2O2 solution and dispersing it into the chamber
• A diffusion phase, where hydrogen peroxide vapor permeates the chamber killing any surface bacteria, chamber pressure is reduced and plasma discharge is initiated
• A plasma phase, where an electromagnetic field is created breaking vapor apart and producing a low temperature plasma cloud of free radicals, such as hydroperoxyl and hydroxyl, that are known to be reactive with most of the essential molecules for normal metabolism of living cells
• A vent phase, where the chamber is vented to equalize pressure allowing the door to be opened (there is no need for aeration or cool down, which means that the chamber is ready for immediate reuse)

Procedure

The sterilization procedure begins by placing the object that requires sterilization in a vacuum chamber, where hydrogen peroxide, at a minimum concentration of 6 mg/L, is injected and vaporized. The hydrogen peroxide gas is then allowed to diffuse throughout the sterilizer load for approx. 50 min. A radiofrequency energy of 400 watts is applied to create hydrogen peroxide gas plasma. Next, the hydrogen peroxide plasma is broken apart into reactive radicals that collide with and kill microorganisms. At the end of the plasma phase, the reactive radicals lose their high energy and recombine to form oxygen, water and other nontoxic byproducts. The plasma is maintained for a long enough period to ensure complete sterilization. A standard plasma phase lasts aprox.15 min. The total sterilization procedure takes approximately 1 h. The H2O2 low temperature plasma sterilization is advantageous when dealing with products that are not resistant to high temperature or high pressure.

These products include, but are not limited to: Catheters, special multi-electrode diagnostic catheters, GI endoscopes, micro-catheters of fiber optic soft endoscope, and medical or surgical instruments that are sensitive to water or heat (including operation instrument, orthopedic instrument, endoscope, laparoscope, endocrine surgical instrument etc.).

Challenges

H2O2 sterilization cycles are run in chambers that are heavily sealed to maintain a vacuum. The use of thermocouples or wired systems in general is very difficult if not impossible.

The TrackSense Pro wireless data loggers eliminate the need for feedthroughs. Its ability to store 60,000 data points provide enough memory space for the complete cycle and its small size allows it to be easily placed within the chamber. Using Ellab’s wireless data loggers with the SKY option, provides real-time data sampling without having to worry about violating chamber integrity.

The effectiveness of the H2O2 sterilization cycle depends on the level of pressure and temperature in the cycle, it is therefore important to monitor and validate those parameters throughout the entire process.

H2O2 Sterilization

Different from using EtO, is that H2O2 sterilization is a semidry process, which is why RH% measurements are not absolutely required. Ellab’s high quality, robust sensors provide the utmost measurement accuracy and allow for a complete validation cycle, significantly reducing setup time. TrackSense loggers are made of stainless steel and their electronics are hermetically sealed, protecting from possible oxidation or chemical intrusion.

Method

When validating an H2O2 sterilization process, it is necessary to map the chamber and monitor the different physical parameters involved in a cycle. Particularly, the monitoring of temperature and pressure is essential to evaluating the performance of a H2O2 sterilization cycle. Both empty and loaded chamber tests are required.

It is recommended that the acceptance criteria are formulated from a worst-case scenario perspective.

Depending on the size of the chamber, the relevant number of temperature sensors are selected and only one pressure/vacuum sensor is required. The location of sensors must provide a useful representation of the chamber layout. The creation of a thermal map in an empty chamber provides the location of the most critical points that are to be monitored during the process (hot and cold spots).
If real time data is required, the modularity of the TrackSense Pro equipment offers optional SKY use, displaying live data within the ValSuite software.

Creating and documenting sensor positions is an important part of the documentation. When using the Unit tool with the optional pictures provided in the ValSuite Pro software, it is possible to have documented mapping of sensor placement that will facilitate repeatable and comparable studies. Once the position of the sensors in the vessel have been documented, it is necessary to observe sensor placement inside the product. The ValSuite software facilitates the documentation of the various sensor placements by allowing users to include descriptive pictures for each channel used.

Once all the data is collected, the user must observe the characteristic of the process. When analyzing temperature, it is usually required that the variation in load temperature measurements must not be greater than 2 °C. And the variation in the wall temperature must not be greater than 5 °C.

ValSuite Software

ValSuite provides tools to analyze the performance of the H2O2 sterilizer in all phases of the process. The use of time-markers helps generate graphical and analytical reference points in the collected data. Statistics calculations, such as min., max., delta and the evaluation of the calculated values, are also available in the software. The limit report offers a quick evaluation of the performance of the time that the process was within the established criteria.

The ValSuite Pro software integrates all calculations into self-generated reports without the need to export data into other software. Reports can also include the placement of the loggers inside the vessel and descriptive pictures of sensor positioning. See the sample PDF document. Generating ValSuite reports provides the highest data security for the results due to the 21 CFR Part 11 compliance.

A critical factor when validating any sterilizer is the calibration of probes to demonstrate that they are within an acceptable accuracy. Using the built-in calibration functionality, users can calibrate Ellab sensors at regular intervals. The ValSuite Pro software generates an easy to read calibration report that includes all measurements and tolerances that are defined by the user. It is recommended that Ellab sensors and probes are sent in at least once a year for factory calibration (which includes a traceable calibration certificate).