Aleix Nin

Sterilization is a critical process in various sectors, particularly in scientific research, where the complete eradication of all forms of life from an object is essential for the safety of researchers, the integrity of experimental results, and public health.

In this context, among the numerous available sterilization techniques, the isothermal cycle or low-temperature cycle using steam autoclaving stands out as an innovative and efficient solution for processing heat-sensitive objects or substances.

This process, conducted at a consistently low temperature, is ideal for disinfecting, pasteurizing and sterilizing instruments and materials that cannot withstand the high temperatures used in conventional sterilization cycles. In fact, low-temperature sterilization is often the only viable option for processing thermolabile loads, such as certain plastics, electronic devices, and biological solutions.

The principle behind isothermal sterilization is to maintain the temperature at a level that is sufficiently high to destroy any microorganisms, yet low enough to avoid causing irreversible damage to the materials being processed.

This balance is achieved through the use of carefully designed programs that maintain a constant temperature throughout the process. These programs are typically either of long duration or repetitive. This technique ensures that heat is uniformly and effectively distributed across all surfaces of the load, thereby destroying any form of life without compromising the structural integrity of the instruments or materials processed.

A significant advantage of this method is its ability to sterilize without altering the physical or chemical properties of the treated objects. This is particularly important for complex electronic devices, such as certain implants, which may have components that are thermolabile or sensitive to excessive moisture.

In the research and development of pharmaceutical and biotechnological products, preserving the physicochemical properties of proteins is crucial. For instance, in the preparation of specific culture media, the low-temperature isothermal cycle allows these products to be sterilized without overheating, thus preventing degradation or alteration of their formula, and preserving their fertility rates.

Principles of isothermal processing

Isothermal processing, an advanced technique in the field of sterilization, is grounded in specific thermodynamic principles to achieve effective pasteurization or sterilization of heat-sensitive materials. This method is distinguished by its approach of maintaining a constant temperature throughout the process, allowing for safe and effective pasteurization or sterilization without compromising the integrity of the treated objects.

Thermodynamic foundations

The isothermal process is characterized by its ability to maintain a constant system temperature. In the context of autoclave sterilization, this implies that heat transfer to or from the system is managed in a manner that preserves thermal equilibrium. This equilibrium is crucial for preventing temperature fluctuations that could damage sensitive materials or cause insufficient lethality in certain regions of the load.

Isothermal sterilization leverages this principle to ensure that the temperature remains within a specific range, sufficient to destroy microorganisms without reaching the thermal damage point of the structure or composition of the sterilized objects.

Differentiation from other sterilization methods

Unlike conventional sterilization methods, such as high-temperature steam sterilization, the low-temperature cycle does not rely on brief exposures to very high temperatures to achieve sterilization. Instead, it focuses on a less aggressive approach, utilizing prolonged exposures at lower temperatures.

While traditional methods typically operate at temperatures exceeding 120°C, isothermal sterilization operates at a much lower temperature range, making it ideal for materials that cannot withstand extreme heat.

Mechanism of action

The mechanism of action in isothermal steam autoclave sterilization involves the use of controlled temperature moist heat to destroy microorganisms. Moist heat is effective at denaturing the proteins within the cell walls of microorganisms, leading to their death or inactivation.

By operating at lower temperatures, this method reduces the risk of damaging heat-sensitive materials, such as certain plastics, electronic devices, and biological preparations.

Applications of the isothermal Cycle

The isothermal sterilization cycle, characterized by its ability to operate at controlled and constant temperatures, has a broad spectrum of applications, particularly in environments where the integrity of heat-sensitive materials is of paramount concern.

This method has become an indispensable tool across various fields, ranging from scientific research to the production of pharmaceuticals.

• Use in microbiology laboratories for the preparation of culture media

In the realm of microbiology laboratories, the isothermal cycle is often used for the preparation of culture media and agar. These materials are crucial for the cultivation of microorganisms in microbiological and biotechnological studies. Isothermal sterilization ensures that these media are sterilized without altering their chemical composition.

• Sterilization of sensitive materials in research

The isothermal cycle is also employed for the sterilization of a variety of sensitive materials used in research. This includes certain types of plastics, chemical reagents, and biological components that could degrade or lose their efficacy under more aggressive sterilization conditions.

The ability to precisely control the temperature allows these materials to be sterilized safely, preserving their integrity and properties.

• Sterilization of thermolabile medical devices

One of the most critical applications of the low-temperature cycle is in the sterilization of medical devices. Many of these devices contain components that are sensitive to high temperatures, such as certain plastics, adhesives, or integrated electronic components.

Isothermal sterilization enables effective sterilization of these devices without compromising their functionality or structural integrity. This is particularly relevant for advanced surgical instruments, implants, and diagnostic devices that require a high degree of precision and reliability to operate effectively.

Configuration and temperature range in isothermal sterilization

The configuration and temperature range are critical aspects of the isothermal sterilization cycle, determining its efficacy and applicability in various contexts. The flexibility in temperature configuration allows the isothermal cycle to adapt to a variety of specific needs, ensuring the effective sterilization of heat-sensitive materials without compromising their integrity.

Operating temperature range

The low-temperature cycle typically operates within a temperature range of 70°C to 95°C. This range is significantly lower than the temperatures used in conventional sterilization methods, such as high-pressure steam cycles, which commonly reach 121°C or higher.

The ability to operate at these lower temperatures is what makes the isothermal cycle ideal for materials that cannot withstand extreme heat.

Temperature settings and flexibility

One of the most notable advantages of the isothermal cycle is its ability to adjust the temperature according to the specific needs of the material being sterilized.

This flexibility allows users to select the optimal temperature that ensures the effective elimination of microorganisms while minimizing the risk of thermal damage to sensitive materials.

This adjustment capability is highly advantageous in applications where different materials require different levels of thermal exposure.

Precise temperature control

Precise temperature control is fundamental in the isothermal cycle. Autoclaves equipped for isothermal cycles are designed with advanced temperature control systems that maintain the desired temperature with minimal variation.

This precise control is essential to ensure that the entire sterilization process is carried out uniformly and effectively, avoiding cold spots that could lead to incomplete sterilization and hot spots that could damage the structural integrity of the load.

Advantages and limitations of the isothermal sterilization cycle

The isothermal sterilization cycle, characterized by its use of controlled and constant temperatures, presents several significant advantages, particularly in the treatment of heat-sensitive materials. However, like any method, it also has certain limitations that must be considered.

Advantages of the low-temperature or isothermal cycle

• Protection of heat-sensitive materials

The primary advantage of the isothermal cycle is its ability to sterilize materials that cannot withstand the high temperatures of conventional methods. This includes certain plastics, electronic devices, and biological materials, whose integrity remains largely intact after processing.

• Precise temperature control

The isothermal cycle allows for precise control of temperature, which is crucial for ensuring effective sterilization without exceeding the thermal damage threshold of the materials.

• Efficacy in microorganism elimination

Despite operating at lower temperatures, the isothermal cycle is effective in eliminating a large part or the totality of microorganisms, including bacteria and viruses, by operating over much longer time periods. This ensures safety and sterility.

• Versatility in various applications

Its ability to be adjusted to different temperature ranges makes it suitable for a wide range of applications, from the sterilization of medical devices to the preparation of specific culture media in microbiology laboratories.

Limitations of the low-temperature or isothermal cycle

• Longer cycle time

Due to the lower temperatures used, isothermal cycles often require significantly more time to achieve effective sterility compared to high-temperature methods. This could be a limiting factor in environments with high turnover and where productivity is a critical metric.

• Restrictions on types of materials

While ideal for heat-sensitive materials, the isothermal cycle is not suitable for all types of items. Some objects may require the higher temperatures of traditional methods to ensure adequate sterilization, especially those heavily contaminated or containing prions or spores.

• Cost and equipment availability

Autoclaves capable of performing isothermal cycles tend to be more expensive and less common than standard autoclaves, which could limit their accessibility in economically constrained settings.

• Specific safety and maintenance considerations

The operation and maintenance of these autoclaves are comparable to standard autoclaves, requiring specific knowledge and, in some cases, additional precautions. This is particularly true regarding periodic checks to certify the proper functioning of the equipment.

Standard operating procedures and protocols in isothermal sterilization

The correct implementation of an isothermal sterilization protocol necessitates thorough preparation and validation testing. These steps are critical to ensure the efficacy of the sterilization process, preserving the safety and integrity of the treated materials.

1. Preparation of materials

   Prior to sterilization, all materials must be meticulously cleaned and disinfected. High microbial load on items to be sterilized hinders effective sterilization. Organic or inorganic residues can interfere with the sterilization efficacy. Materials should be arranged to allow free air circulation.

2. Loading the autoclave

   Materials must be placed in the autoclave in a manner that allows uniform heat distribution. If baskets are stacked, the bottom of the upper basket should not touch the materials in the lower basket. Avoiding chamber overloading is crucial to ensure effective sterilization.

   It is recommended to select the combination of temperature and time based on the material type and the manufacturer’s specifications of the object to be processed.

3. Sterilization process

   Once the autoclave is loaded and the cycle selected, the autoclave program is initiated. The equipment will heat up, raising the internal chamber temperature to the set value for the isothermal cycle.

   During the cycle, the temperature remains constant at the set value or within the selected range. Temperature stability is essential for process efficacy. Modern isothermal autoclaves are equipped with controls to monitor and adjust temperature and pressure, ensuring the cycle stays within the established parameters.

4. Cycle completion and post-process

   Upon cycle completion, materials must be cooled in a controlled manner to prevent condensation and damage from abrupt temperature changes. Once cooled, materials can be removed from the autoclave.

   It is important to handle them with care to maintain sterility. Sterilized materials should be stored in a clean, dry environment to avoid recontamination.

5. Safety and maintenance considerations

   Operators must be adequately trained in the use of the autoclave and adhere to all safety measures, including the use of personal protective equipment.

   Additionally, autoclaves should undergo regular maintenance to ensure optimal performance and safety.

The flash sterilization cycle is a fast and effective sterilization method widely used in emergency situations in various sectors such as healthcare and microbiology. This procedure is conducted in steam autoclaves and is essential for scenarios requiring the rapid processing of solid objects for immediate application.

What is flash sterilization?

Flash sterilization is a specialized cycle for autoclaves equipped with steam generators, vacuum systems, and final drying mechanisms. This process necessitates the use of high-quality steam and systems designed to eliminate any cold air pockets. The process is divided into the following stages:

Stages of the flash sterilization cycle

1. Purge or air removal phase

   It is essential to expel all air from the chamber to ensure that steam can penetrate all surfaces of the load. In the flash cycle, a single vacuum pulse is employed to save time.

2. Heating phase

   Following the purging phase, the autoclave injects high-temperature steam into the chamber until the sterilization temperature is reached.

3. Sterilization phase

   This stage is shorter in duration compared to a standard cycle due to the use of a sterilization temperature exceeding 130ºC.

4. Drying phase

   After the sterilization phase, the autoclave initiates the drying phase. Typically, this process involves a heating jacket that raises the temperature of the chamber walls and the objects inside, while a vacuum pump expels all moisture to the exterior. By the end of this stage, the load will be completely dry.

Importance of flash sterilization

Flash sterilization is crucial in emergency situations or when a rapid turnaround of instruments is required. While this procedure is used in research and microbiology settings, its significance is particularly notable in healthcare contexts. Its widespread use in these environments is due to its convenience and speed, despite being a cycle with higher failure risks compared to a standard cycle. This is because it is generally preferable to use a fractionated prevacuum consisting of multiple steam pulses rather than a single prevacuum pulse.

The popularity of the flash cycle arises from its ability to provide healthcare professionals with sterilized instruments in minimal time, thereby improving efficiency and response times in critical situations.

Key considerations and constraints in the clinical context

According to recommendations from health technology assessment agencies and regulatory authorities, the short sterilization cycle should only be employed in emergency situations where surgical instruments are urgently needed, such as in cases of accidental contamination during an operation.

Additionally, it must not be used for implantable devices due to the risk of transmitting serious infections. Nor can it be used for instruments that have been in contact with tissues at risk of transmitting prions, especially in patients with or suspected of having spongiform encephalopathy.

While flash sterilization is a viable option in certain contexts, priority should always be given to standard sterilization cycles. To avoid the necessity of flash sterilization, meticulous planning and management of surgical instruments are crucial. It is essential to anticipate and align instrument needs with the volume of scheduled interventions. For instance, maintaining an adequate number of sterilized instrument sets for each procedure helps prevent delays and reduces the need for flash sterilization in urgent situations.

Critical factors in flash sterilization

To ensure effective and safe flash sterilization, it is imperative to control and evaluate the following aspects in each rotation:

• Adequate cleaning and disinfection: Ensure proper cleaning and disinfection of materials prior to sterilization.
• Correct load placement: Position each item correctly to guarantee effective and even steam penetration across all surfaces of the load.
• Validation of sterilization procedures: Validate each sterilization procedure using biological and chemical indicators.
• Safe handling and transport: Ensure the safe handling and transport of materials to avoid recontamination.

Procedures and best practices to optimize the flash sterilization cycle

To ensure the effectiveness of flash sterilization, it is essential to adhere to best practices and procedures, including:

• Proper installation of the autoclave: Ensure the autoclave is installed correctly according to manufacturer specifications.
• Regular cleaning and disinfection: Perform routine cleaning and disinfection of the autoclave chamber and its accessories.
• Comprehensive record-keeping: Maintain detailed records of all cycles performed to track usage and efficacy.
• Regular inspection and preventive maintenance: Conduct regular inspections and preventive maintenance to ensure optimal performance. This includes verifying and calibrating sensors and controls, as well as checking the condition of seals to prevent steam leaks.
• Adequate staff training: Provide thorough training for personnel on the operation and maintenance of the autoclave to ensure proper usage and safety.

Conclusions

In the clinical context, flash sterilization should be reserved for emergency situations where surgical instruments are needed immediately, and other methods are not feasible. For its proper application, it is crucial to follow strict guidelines and procedures to ensure the safety and effectiveness of the sterilization process, as the health and safety of patients are paramount.

 

Sterilization plays a crucial role in various branches of the life sciences, being particularly vital in sectors such as pharmaceuticals, food industry, and microbiology. In this context, the F₀ cycle in autoclaves marks a significant advancement as it allows the professionalization of sterilization processes, making it indispensable for experienced users working under high-quality standards.

This method not only ensures the complete inactivation of any form of life but also enables the quantification and evaluation of the efficiency of a sterilization process. It facilitates the comparison of the efficacy of different sterilization cycles at various temperatures and even between methods employing different sterilization technologies.

The F0 cycle is based on the concept of thermal equivalence, where the F₀ value represents the equivalent minutes of sterilization at 121.1°C. For instance, a sterilization cycle with a F₀ of 3 indicates a process equivalent to subjecting a load to 121.1°C for 3 minutes. Moreover, this same F₀ of 3 can be achieved by sterilizing for 12 minutes at 115°C or 5 minutes at 119°C. Therefore, 3 minutes at 121°C is equivalent to 12 minutes at 115°C or 5 minutes at 119°C.

This approach makes it possible to quantify the sterility of a load and adjust the sterilization process according to the particular needs of what is being sterilized. Additionally, when an F₀ autoclave is used together with a central flexible probe, the temperature inside the load can be measured and a sterilization process can be regulated by the F₀ value obtained in the load itself and not by the chamber temperature, avoiding errors of lack of efficacy due to too short exposure times.

The great versatility of the F₀ cycle is very advantageous in contexts where exposure to high temperatures may compromise the integrity of the load. It is also especially useful in contexts where accuracy and recording of the degree of sterility achieved in each process is vital. Also in the sterilization of large volumes of liquids, since this type of loads take a long time to heat up and cool down, so if we run a program for F₀=3, the autoclave will calculate the sum of all the F achieved in each second, adding all the area un the curve, and will end the cycle when reaching the equivalent exposure of 3 minutes at 121.1°C but thanks to this thermal equivalence, it will achieve this F₀=3 without ever reaching 121.1°C at any time.

If at some point you got lost, don’t worry, understanding the concept of F₀ is not a simple matter. Below we will explain everything you need to know about the F₀ value and F₀ autoclaves.

Principles of F₀ autoclaves

Sterilization using F₀ in autoclaves is a process that integrates science, precision, and technology to effectively eliminate microorganisms. This method is grounded in fundamental physical principles related to energy transfer between two bodies and ensures the safety and efficacy of scientific experiments and production processes across a wide range of applications and industrial sectors. Below, we explain some of these basic principles:

Concept of F₀

The heart of F₀ sterilization is the F₀ value, a parameter that quantifies the lethality of a sterilization process. It is defined as the equivalent exposure time at a reference temperature of 121.1°C required to achieve a specific level of sterility. This concept allows for the standardization and comparison of different sterilization cycles, ensuring they all achieve an equivalent level of sterility.

F₀ formula

Δt = time interval between two successive measurements of T
T = temperature of the sterilized product at time t
z = temperature coefficient, typically assumed to be 10°C

Although the theoretical and mathematical justification of the F₀ formula is beyond the scope of this post, two related concepts must be understood: the D-value and the Z-value.

• D-value, called decimal reduction time. Indicates the thermal susceptibility of a microorganism at a constant temperature. It is defined as the time required to destroy 90% of the microorganisms in a sample. For example, a D=1 corresponds to a 90% reduction, a D=3 to a 99.9% reduction, and a D=6 to a 99.9999% reduction. Typically, a D=1 is used, so it does not usually appear in the formula.
• Z-value, known as thermal resistance factor. This value shows how the inactivation of a specific microorganism varies with changes in the process temperature. As one might imagine, the inactivation caused by a sterilization process at 120°C for one minute differs significantly from that at 110°C for the same period.

Importance of temperature and time

In F₀-controlled sterilizations, temperature and time are interdependent variables conditioned by the reference temperature and the maximum exposure temperature of the process. Thus, an F₀ sterilization cycle offers a wide range of configuration possibilities.

In any case, higher temperatures require less time to reach the same F₀ value, and vice versa. This relationship is crucial for adjusting sterilization cycles according to the specific needs of materials or products without compromising process efficacy.

Calculation in real time

F₀ autoclaves are equipped with microprocessors that allow real-time calculation of the achieved F₀ value every second. These systems continuously monitor the temperature within the autoclave and/or within the load, adjusting the sterilization cycle to ensure the desired F₀ value is reached according to selected preferences. This capability is particularly useful for mitigating variations in the load or operational conditions of the autoclave.

Effective and safe sterilization

By using the F₀ value to govern the sterilization cycle, autoclaves can ensure effective sterilization in any scenario. This is crucial in environments where ensuring the complete sterility of the load is essential, such as hospitals, laboratories, and the production of food and pharmaceuticals.

Advantages of the F₀ cycle in autoclaves

F₀ autoclaves represent a significant advancement in sterilization technology, offering multiple advantages over traditional methods. These benefits not only enhance the efficiency and effectiveness of the sterilization process but also contribute to greater safety and adaptability in various industrial and healthcare environments. Some of the main advantages of F₀ autoclaves include:

1. Improved accuracy and precision in sterilizations

   One of the major advantages of F₀ autoclaves is their ability to quantify the lethality of a sterilization process with high precision and accuracy. By utilizing the F₀ value, these autoclaves can adjust time and temperature to ensure the desired level of sterility is achieved, regardless of environmental or load variations.

2. Greater flexibility in handling different loads

   F₀ autoclaves are exceptionally adaptable to different types of loads. They can effectively sterilize a wide range of materials, from medical instruments to pharmaceuticals and food products, by automatically adjusting sterilization parameters for each type of load to ensure consistent sterility.

3. Efficacy and flexibility across a wide range of scenarios

   Thanks to the precise control of temperature and time, F₀ autoclaves are effective in a wide variety of scenarios, including those requiring gentler temperatures due to the thermolability of the load, such as food items, or higher temperatures for faster processes where the load can withstand greater heat exposure.

4. Time and energy savings

   By optimizing sterilization cycles based on the F₀ value, these autoclaves can significantly reduce the total sterilization time. This not only saves time but also reduces energy consumption, thereby lowering operational costs and minimizing environmental impact.

5. Enhanced process safety

   The ability to monitor and adjust the sterilization process in real time significantly enhances safety. This is particularly important in environments where sterility is critical, such as healthcare settings and industry, as it reduces the risk of human error and inconsistencies in how each user loads the autoclave in terms of disposition and quantity of processed items.

6. Record keeping and documentation

   Modern F₀ autoclaves often include advanced recording and documentation capabilities, which are essential for complying with industry regulations, ensuring high-quality processes, and maintaining accurate records for process validation and audit purposes.

Automation of F₀ sterilization in autoclaves

The automation of F₀ autoclaves has revolutionized the sterilization process, elevating it to new levels of efficiency and reliability. This automation not only simplifies the sterilization process but also ensures greater consistency and precision in each batch processed.

F₀ autoclaves are equipped with automated systems that precisely control and adjust the temperature and sterilization time. This ensures that each sterilization cycle achieves the desired F₀ value, regardless of variations in load or operating conditions. This ability to calculate the F₀ in real time allows the autoclave to make automatic adjustments during the cycle. If the system detects that the accumulated F₀ is lower than the target, it will prolong the cycle to ensure effective sterilization. Conversely, if the system detects that the target F₀ has already been achieved, it will terminate the sterilization phase.

Additionally, many F₀ autoclaves can be integrated with centralized management systems, enabling remote control and monitoring, as well as the collection, recording, and analysis of data for continuous process improvement.

Practical applications of F₀ autoclaves

Sterilization using F₀ autoclaves represents not only a technical achievement in microbiology and sterilization but also has extensive and crucial practical applications across various sectors. These applications underscore how this technology has become an indispensable component in numerous environments. Below, we explore some of the most prominent practical applications:

• Medical and hospital settings

In hospitals and clinics, F₀ autoclaves are employed to sterilize surgical instruments, medical equipment, and other materials. The precision and efficacy of F₀ sterilization ensure that these instruments are safe for use in medical procedures, thereby reducing the risk of infections and enabling professional traceability of each batch.

• Research and biotechnology laboratories

Laboratories that work with cell cultures, biological samples, and pathogens rely on sterilization to maintain a contaminant-free environment. F₀ autoclaves provide the necessary safety to conduct research and experiments in a sterile setting. A practical example in this sector is the preparation of large quantities of culture media, which may be demanded at varying scales. Thanks to F₀ autoclaves, a consistent sterilization program can be executed regardless of the volume, whether sterilizing 5 bottles of 1L or 20 bottles of 1L. The program ensures that both processes achieve the same level of sterility, reducing the risk of contamination due to inadequate sterilization due to load variability ebtween different rotations.

• Pharmaceutical industry

The production of pharmaceuticals requires stringent control over the sterility of each batch to ensure the safety and efficacy of the products. F₀ autoclaves are used to sterilize raw materials used in drug manufacturing, as well as finished forms and packaging. This technology also facilitates continuous improvement and automatic recording of all processes, enhancing quality control.

• Food industry

In food production, particularly in preservation and packaging, sterilization is essential to prolong the shelf life of products and prevent spoilage. F₀ autoclaves are critical in ensuring that packaged foods are free from microorganisms while preserving the organoleptic properties of the finished products. These autoclaves are often equipped with fast cooling systems. By employing sterilization cycles regulated by F₀, unnecessary overcooking of foods is avoided. Once the target F₀ value is reached, fast cooling begins automatically, efficiently cooling the load and ensuring the quality of the sterilized food.

 

In the field of sterilization technology, the introduction of the cycle with pressure support in autoclaves represents a significant advancement, particularly concerning the sterilization of packaged products such as collyriums, vials, pre-filled syringes, pouches, and canned foods.

Understanding this process begins with recognizing the necessity of controlling the pressure differential between the interior of the packages and the chamber pressure during the sterilization and cooling phases.

To mitigate the risk of excessive pressure differentials, cycles with pressure support have been developed, incorporating the strategic use of compressed air. Through controlled injection of compressed air into the sterilization chamber, these cycles minimize the pressure differential, thereby preserving the structural integrity of the processed containers.

Types of cycles with pressure support

Cycles with pressure support in autoclaves have two main variants: the Air over-pressure cycle and the steam-air-mix cycle. Each variant is designed to meet specific needs and adapt to different types of loads.

Air over-pressure cycle

The air over-pressure cycle, also referred to as air ballast, represents an advanced adaptation of the standard liquids cycle. This technique integrates the use of compressed air with a fast cooling system, specifically designed for the sterilization of semi-open containers. The primary advantage of this method lies in its ability to minimize liquid loss due to evaporation during the cooling phase, making it particularly suitable for contexts where even minimal liquid loss is unacceptable. This cycle is commonly employed for sterilizing items such as preloaded pipettes, vials containing solutions, glassware covered with aluminum foil, and other containers that allow partial ventilation.

As previously discussed in our post on the standard cycle for the sterilization of liquids, it is crucial to perform controlled and gradual depressurization during the cooling phase to prevent sudden boiling of the contents. However, the standard liquid cycle fails to address the issue of liquid mass loss due to evaporation that occurs from the end of the sterilization phase through to the conclusion of the cooling phase. To mitigate this issue, the air over-pressure cycle introduces compressed air into the chamber to maintain pressure, thereby reducing the partial pressure of the vapor. This reduction, in conjunction with accelerated decreasement of the temperature thanks to the fast cooling system, significantly reduces the evaporation of the load, allowing the materials to cool rapidly without substantial liquid mass loss.

Functionally, the air over-pressure cycle bears similarities to the steam-air mix cycle, as both methods pressurize the autoclave chamber using a combination of steam and compressed air. However, while the steam-air mix cycle incorporates air during both the sterilization and cooling phases, the pressurized cycle differentiates itself by injecting compressed air exclusively during the cooling phase.

While the steam-air mix cycle is generally applied in scenarios where sealed containers develop high internal pressure and risk deformation or rupture, the air over-pressure cycle aims to minimize evaporation loss of the liquid load during the cooling phase, offering an optimal solution for the preservation of liquids in semi-open containers.

A clear application example where the air over-pressure cycle is preferable is in the processing of semi-open bottles containing culture media or in the pharmaceutical sector when processing small-volume containers where water loss due to evaporation is unacceptable.

Typically, autoclaves capable of performing cycles with pressure support are also equipped with a fast cooling system, such as an internal fan and an external water-cooled coil surrounding the chamber.

The combination of both systems, accelerating temperature reduction and elevating chamber pressure, prevents load evaporation, enabling a final phase of the cycle with minimal or no liquid mass loss.

Steam-air-mix cycle

As we have discussed, the air over-pressure cycle involves the strategic use of compressed air during the cooling phase to prevent the evaporation of liquids in partially or fully open containers. However, for the sterilization of hermetically sealed objects, a different cycle, known as the steam-air-mix cycle, is required.

The necessity for this cycle arises from the fundamental need to equalize the internal and external pressures of containers to prevent deformation or rupture due to the thermal expansion of its contents when heated to temperatures exceeding 120ºC.

As illustrated in the image, the injection of compressed air into the chamber during the sterilization phase ensures that there is no excessive pressure differential between the internal pressure of the container and that of the chamber.

However, as you may be aware from reading our blog attentively, the introduction of cold air into the chamber acts as a thermal insulator and hinders the access of steam to the surfaces of the load. This is because most of the gases that compose air, such as nitrogen or carbon dioxide, are non-condensable gases.

These gases prevent the steam from condensing on the surface of the load, thereby impeding the heat transfer from the steam to the load, which slows down the heating of the load and reduces the efficacy of the sterilization process. Therefore, any autoclave performing steam-air-mix cycles must be accompanied by a robust homogenization system that ensures an excellent stability and homogeneity of temperature throughout the load throughout the entire duration of the sterilization phase.

These systems employ techniques that mechanically agitate the atmosphere or even the load itself. Examples of such systems include radial fans or agitation systems.

After completing the sterilization phase, similar to the air over-pressure cycle, high pressure is maintained in the chamber to protect the structural integrity of the load while the chamber temperature, and consequently the internal pressure of the processed items, decreases.

As in the air over-pressure cycle, the steam-air-mix cycle is usually accompanied by a fast cooling system. However, a significant difference is that when dealing with hermetically sealed containers, the fast cooling system often employed involves the direct injection of cold water into the chamber. This method is particularly prevalent in the food industry, where cold water immersion via spray showers is used to cool down canned products or pouches following the sterilization phase.

A practical example illustrating the necessity of this type of cycle is the sterilization of pre-filled syringes. During the sterilization phase, without adequate pressure support, reaching 121ºC could cause the liquid inside the syringe to force the plunger outward due to the internal pressure created during this phase. Conversely, during the cooling phase, if the chamber pressure is not controlled and decreases gradually, it could surpass the internal pressure within the plunger at some point, pushing it inward, resulting in the syringe breaking and becoming unusable. Therefore, it is crucial to use compressed air carefully in both phases of the cycle to ensure that the pressure differential between the inside and outside of the syringe is never excessive.

Practical applications of cycles with pressure support

As observed, cycles with pressure support are indispensable across various industries for processing a wide range of products. In the pharmaceutical industry, these cycles are crucial for processing pre-filled syringes, vials containing solutions, and other pharmaceuticals in liquid form packaged in containers. Without proper pressure control, these items could deform or break. Therefore, maintaining the structural integrity of these containers is essential for ensuring the sterility of the final product and its long shelf life, preventing contaminations that could have severe health implications for patients.

In the food industry, cycles with pressure support are essential for the sterilization of canned and packaged food products. These products, when subjected to high temperatures during sterilization, could undergo deformation or even rupture if the internal and external pressures are not balanced adequately. Specifically, steam-air-mix cycles cycles followed by fast cooling are widely utilized in the sterilization of products such as sauces, pâtés, and ready meals, where it is vital to preserve both the quality of the packaging and the organoleptic properties of the content.

Another significant area of application is research and clinical laboratories. Laboratory materials, such as culture media in bottles, require processing with an air over-pressure cycle to prevent volume loss due to evaporation.

In summary, cycles with pressure support provide a versatile and effective solution for a wide range of applications, enabling the sterilization of pressure-sensitive products without compromising their structural integrity or content. The selection of the appropriate cycle depends on the nature of the material to be sterilized, the type of container, and the specific requirements of each process.

Safety and efficacy considerations

The implementation of cycles with pressure support in autoclaves aims not only to enhance the efficiency of the sterilization process but also to address critical safety and quality concerns. It is imperative to ensure that the selected cycles and parameters are appropriate for the specific application. This necessitates comprehensive validation of the process for each material type and load configuration.

Safety during autoclave operation is of paramount importance. The injection of compressed air and the handling of high pressures must be meticulously managed to prevent risks such as container ruptures, explosions, or malfunctions of the equipment. Autoclave monitoring systems must be designed to detect and correct any deviations from established parameters, thereby ensuring safe and effective operation.

From an efficacy standpoint, the proper distribution of heat and pressure within the sterilization chamber is crucial to ensure that the entire load receives the necessary treatment to achieve sterility, specially in steam-air-mix cycles. Therefore, homogenization systems and/or mechanical agitation, such as radial fans, are essential for maintaining an uniform atmosphere within the chamber in applications where this cycle is employed. These systems must undergo regular maintenance to ensure their optimal functionality.

Furthermore, it is important to consider the environmental impact of cycles with pressure support as they are often accompanied by a fast cooling system. The substantial water consumption required for cooling can be significant. Therefore, optimizing these cycles to minimize resource consumption without compromising the efficacy of the process is a key consideration for sustainable operation.

In conclusion, cycles with pressure support in autoclaves represent an advanced solution for the sterilization of products sensitive to pressure and temperature, combining efficiency with safety. The correct implementation and management of these cycles require a profound understanding of the underlying physical principles, as well as a commitment to operational quality and safety.

The sterilization cycle with temperature segments or ramping represents an advanced technique employed in specialized research fields such as microbiology, food technology, and packaging development. This strategy is employed for the safe production of food, the validation of the structural integrity of packaging, and the assessment of the robustness of innovative materials, while ensuring the efficient eradication of microbial contaminants.

Unlike the flash sterilization cycle, which is characterized by its rapidity and high temperatures, this process involves a sequence of stages at varying temperatures and pressures, carefully adjusted in both the pre-sterilization and post-sterilization stages.

What does sterilization with temperature segments involve?

This sterilization method is ideal for conducting tests that evaluate how temperature and pressure impact the physicochemical properties of a product. Such tests are particularly significant in research environments aiming to design new products, in quality control stress tests, and in the creation of pilot batches in the food industry.

To perform these tests, it is essential to have an autoclave integrated with vacuum and air compression systems, which facilitate the precise modulation of temperature and pressure conditions throughout the cycle. This capability is especially relevant in research environments, quality control, and stress testing.

Stages of the sterilization cycle with temperature segments

Typically, the cycle consists of several stages, each adjusted to specific parameters of duration, pressure, and temperature. In more specialized autoclaves, the rate at which temperature and pressure increase between segments can also be adjusted. The main phases are as follows:

• Prevacuum phase

Initially, air is removed from the chamber to ensure complete steam penetration. This stage is crucial for sterilizing porous loads, objects with cavities, and instruments with complex geometries.

• Heating phase with temperature segments

Next, the heating phase begins, where the cycle is divided into several segments or ramps, each with a specific set of conditions for duration, pressure, and temperature. These segments are designed to gradually heat the load and prepare it for the sterilization phase. The transition between each segment may include stabilization periods to ensure that each change in conditions occurs in a controlled manner.

• Sterilization phase

At this point, temperature and pressure are stabilized for a predetermined time to ensure the complete sterilization of all objects within the chamber.

• Cooling phase with temperature segments

In the final stage, temperature and pressure are gradually reduced to return to normal conditions, preparing the objects for safe removal from the chamber. Optionally, this stage can also be structured into several segments, each with specific conditions of pressure and temperature.

These segments are designed to control the gradual reduction of the chamber’s temperature. Similar to the heating phase, the transition between these segments can include stabilization stages to ensure that the cooling of the load is controlled and uniform.

Importance of sterilization cycles with multiple segments

As previously mentioned, these cycles are ideal for researchers and experienced users, as they allow for detailed programming by time, pressure, and temperature. This ensures precise adaptation to the specific needs of each application. Additionally, these segments can be incorporated both before and after the sterilization phase, offering exceptional flexibility in process management. Below, we describe some examples of industries that utilize these types of cycles.

In the food packaging industry, cycles with segments are useful for several reasons, particularly for researchers and production operators handling plastic trays and other sensitive materials.

They are also widely used in the food industry and catering when cooking segments are preferred before reaching the sterilization temperature. This method allows raw foods to be cooked and sterilized within the same process. Popular applications include the preparation of sautéed foods where the semi-cooked preparation is packaged, or the cooking of meat and vegetables.

In microbiology, sterilization cycles with temperature segments are used for the preparation of special culture media containing thermolabile substances. In this process, the culture medium is first sterilized, then cooled, followed by the injection of antibiotics or thermolabile nutrients, and finally, the temperature is increased again to pasteurize the preparation.

A classic example is the preparation of blood agar. This process requires initial sterilization at 121°C for 15 minutes, cooling to 50°C, injecting the blood, pasteurizing for 15 minutes at 72°C, and then cooling again to 45°C.

Key considerations of sterilization with temperature segments

To ensure the effectiveness of sterilization with multiple temperature segments, it is essential to consider:

• Autoclave technology and components: ensure that the autoclave being used possesses the appropriate technology and components to perform these cycles.
• Material quality and preparation: monitor the quality and adequate preparation of the materials to be sterilized.
• Qualification after installation and annual calibration: calibrate the equipment annually and strictly follow the preventive maintenance plan established by the manufacturer.
• Operational and safety procedures: maintain a strict adherence to operational and safety procedures.
• User training: train all users who will handle the autoclave.
• Sterilization process validation: validate the sterilization process through the use of biological and chemical indicators.

Conclusions

The sterilization cycle with multiple segments or ramps is established as an advanced methodology, crucial for specialized applications in fields such as microbiology, the food industry, and packaging. This process, characterized by its sequence of controlled temperature and pressure stages, significantly differs from traditional sterilization methods due to its flexibility to meticulously adapt to the specific needs of different products and materials.

Although its implementation may be more complex than traditional methods, the ability to customize sterilization conditions makes it an invaluable tool for a wide range of applications in research and quality control.

 

The accelerated aging cycle in autoclaves constitutes a technique employed in specialized research and quality control laboratories across various sectors, including the electronics, construction, medical devices and packaging industries. This method is essential for validating the structural and functional integrity of novel materials.

In contrast to conventional sterilization methods, the accelerated aging cycle is characterized by the implementation of multiple consecutive sterilization cycles conducted continuously within a sealed chamber. This process is designed to subject products to exceptional stress levels, with the objective of thoroughly investigating their durability and response to extreme conditions.

Overview of the process

The cycle commences with the placement of the product into the sterilization chamber, where it is subjected to a series of repetitive sterilization cycles without interruption. These cycles can be maintained uniformly or vary in duration, with maximum temperatures that may either progressively increase or decrease. While conventional applications typically do not necessitate extremely high temperatures, these tests are commonly conducted within a range of 80°C to 134°C.

The objective of this methodology is to simulate the effects of time and adverse conditions that the product may encounter throughout its lifecycle, but within a significantly shortened timeframe. This approach facilitates an accurate and efficient assessment of the durability and reliability of the materials and products under study.

Industrial applications of accelerated aging tests with autoclave

Lifecycle testing cycles using autoclaves hold significant relevance in the development of new materials and products. Below, we explore how this methodology is applied across various industries.

In the electronics industry, the use of this cycle is essential for predicting and ensuring the resilience of electronic components under continuous use. These tests simulate the operational conditions these components may face throughout their service life or during manufacturing, allowing for the anticipation of potential failures and ensuring optimal performance over their lifespan.

Within the construction sector, the accelerated aging sterilization cycle is employed to evaluate the durability and resistance of construction materials under scenarios of artificially accelerated wear and aging. This is crucial to ensure that materials maintain their structural and functional integrity, meeting the required safety standards for buildings and structures.

In the packaging industry, the application of this cycle serves to verify the durability and protective capacity of packaging after being subjected to a standard sterilization process during its useful life. This analysis ensures that packaging will maintain the product’s integrity and protect its contents effectively until it reaches the final consumer.

In the pharmaceutical sector, the importance of these sterilization cycles is even greater, as they are fundamental in determining the shelf life and expiration dates of pharmaceutical products. Simulating stress conditions helps predict the behavior of medications during manufacture and during storage, ensuring their efficacy and safety for patients.

Autoclaves for conducted accelerated aging studies and product lifecycle tests

Before utilizing an autoclave for these purposes, it is essential to ensure that the equipment is equipped with the appropriate technology, pertinent components, and necessary robustness to withstand the stress conditions of these test cycles. The selection of an autoclave should be based on a detailed evaluation of its construction quality, the manufacturer’s reputation, and its durability to endure the demanding test cycles simulating accelerated stress conditions.

To ensure that the autoclave meets these standards, it is advisable to contact the manufacturer directly. Typically, autoclave manufacturers do not design their equipment specifically for conducting accelerated aging tests or lifecycle testing. The intensity of the test cycles requires the use of high-quality materials and components, which can significantly increase production costs.

If you already have an autoclave, a key indicator of its suitability for these tests is its capability to configure custom programs that can execute these accelerated aging cycles repetitively and continuously

If you require an autoclave designed to carry out accelerated aging and product lifecycle tests, we can custom-build it to meet your exact specifications and requirements. Contact us for more information.

 

The vacuum test in an autoclave is a fundamental procedure to ensure the hermetic integrity of the chamber and the piping system of an autoclave, as well as to verify the proper functioning of the equipment’s vacuum system.

This evaluation subjects the autoclave to vacuum conditions, measuring the vacuum loss over time. In this article, we will explain what this test evaluates, its procedure and operation, and when it is recommended to perform it, based on industry best practices and standards.

The importance of proper performance of an autoclave’s vacuum system

For autoclave sterilization to be effective, it is essential that steam comes into contact with all surfaces to be sterilized. This is because steam, as the sterilizing agent, transfers its energy by conduction and condensation, i.e., by transitioning from a gaseous to a liquid state. Therefore, it is crucial that nothing obstructs the steam’s access to the surfaces that need to be sterilized. For this reason, ensuring the creation of a quality vacuum before generating steam is vital.

If air is not properly removed from the chamber, the nitrogen and other gases present in the air act as an insulating barrier between the steam and the object to be sterilized, thereby compromising the effectiveness of the sterilization process.

What does the vacuum test evaluate?

The main objective of the vacuum test is to verify the hermeticity of the chamber and the piping system of the autoclave, ensuring that there are no air leaks that could compromise the sterilization process. This test is crucial to confirm that the sterilization chamber is perfectly sealed, meaning that there is no unexplained decrease in the vacuum level. It helps identify potential failures in the vacuum pump’s operation, the sealing of solenoid valves, the presence of air leaks in the door gasket or pipe connections, and whether the vacuum levels defined by the manufacturer have been achieved.

During the test, the autoclave is subjected to a vacuum cycle, and the amount of vacuum lost over a specific period is measured. A typical cycle includes three vacuum pulses, followed by a 15-minute hold time in a deep vacuum. At the end of the test, the leak rate is measured in units such as kPa/min, mbar/min, or mmHg/min. Most industry standards establish that an acceptable leak rate is 1 mmHg/min or less.

Procedure and operation of the vacuum test

The procedure for conducting a vacuum test includes several stages to ensure the accuracy and reliability of the results. Generally, any pre-vacuum autoclave comes from the factory with the specific program for this test in its program memory. To carry out the test, the following steps should be followed:

1. Preparation: The autoclave must be empty and clean. All removable accessories, such as trays, racks, or supports, should be removed to avoid interference with the test.
2. Cycle Start: The corresponding vacuum test cycle program is executed. The autoclave will start by performing three vacuum pulses, eliminating air from the system and then allowing it to return to atmospheric pressure, repeating this process three times.
   
3. Holding Time: After the three vacuum pulses, the autoclave maintains a deep vacuum for 15 minutes. During this period, the vacuum loss is quantified.
4. Results: At the end of the cycle, the autoclave displays the leak rate. This result is compared with industry standards or the user’s specific criteria to determine if the autoclave passes or fails the test.

As you can see, the correct outcome of this procedure is essential to ensure that the autoclave operates properly and can perform effective vacuum sterilization cycles.

When should the vacuum test be performed?

The frequency with which the vacuum test should be performed depends on the standard operating procedures (SOP) of each laboratory and the risk tolerance of each facility. Logically, centers that sterilize surgical, laparoscopic, or dental instruments will have a shorter interval for conducting this control test than a school microbiology laboratory. However, performing this test regularly is important as it provides evidence of the structural integrity of the autoclave and its vacuum system.

While any autoclave from any manufacturer is calibrated and checked at the factory, it is essential to periodically validate the proper functioning of pre-vacuum autoclaves using this test. This validation includes not only the vacuum test but also other operational tests, such as the Bowie-Dick test, spore tests, or sterilization control tape. Regularly performing these tests is fundamental to maintaining rigorous control over the sterilization process.

In addition to the frequency determined by each laboratory’s SOP, it is advisable to perform the vacuum test after any repair, maintenance, or replacement of the autoclave gasket. These situations can affect the equipment’s performance, and a vacuum test helps verify that everything is working properly.

In summary, the vacuum test is a crucial part of the maintenance and validation of autoclaves with vacuum systems. Its implementation ensures the optimal functioning of these devices, thereby guaranteeing the effectiveness of the sterilization process and the safety of sterilized products.

The significance of the Bowie & Dick test emerged in the 1950s. Numerous hospitals in Great Britain identified deficiencies in the sterilization of some porous materials, such as gowns, papers, and ceramic containers. J.H. Bowie and J. Dick were two prominent researchers who sought a solution to this problem, which they successfully developed in 1963. This solution is now known as the test that bears their names.

Due to its importance, the British Ministry of Health included it in their daily testing regimen for all autoclaves in healthcare environments.

Currently, the Bowie & Dick test is used in laboratories worldwide, and in Spain, its use is recommended under the UNE-EN-ISO 17665 standard, “Sterilization of healthcare products.” In fact, this standard is derived from EN-554, “Validation and routine control of steam sterilizers,” which was adopted in Spain as UNE-EN-554.

Its closest antecedents date back to 2009, when the EN-17665 standard (Sterilization of health care products — Moist heat — Part 1: Requirements for the development, validation, and routine control of a sterilization process for medical devices) came into effect, replacing the EN-554:1995 standard.

In addition to being a test that measures the proper performance of an autoclave, the results can be used as expert evidence in cases of critical failures and legal contexts. For this reason, it is advisable to keep any obtained results and archive them properly with their corresponding date.

What does the Bowie & Dick test evaluate?

It is quite simple: the test evaluates whether the sterilization of certain porous components has been performed correctly.

This helps determine if the machine can effectively sterilize some types of materials. In other words, it is a test whose results diagnose the correct functioning of the autoclave. The Bowie & Dick test indicates whether steam penetration into the test pack was rapid and uniform and, therefore, whether it is possible to sterilize permeable and/or porous items. The test consists of a thermosensitive strip or sheet of paper (sensitive to heat), which changes color, typically from white to black, during the sterilization process. This color change indicates exposure to heat and steam.

There are different shades (pink, blue, etc.), depending on the brand. This sheet is placed in the center of a so-called pack, composed of foam rubber and other fibrous layers. One of the main characteristics of the paper sheet is the distinct geometric pattern of visible marks.

For the color change in the thermosensitive paper to occur, there must be a simultaneous increase in temperature and humidity. The resulting pattern and distribution provide insight into the sterilization process’s effectiveness.

There is one important fact, and that is that the exposure period must be at least 3.5 minutes, and the temperature range should be between 132 and 134℃.

The kit can be used to measure:

• The effectiveness of steam penetration in porous components.
• The temperature and pressure of steam during the sterilization phase.

Procedure and operation of the test

The test kit should not be prepared independently. Prepared kits available from manufacturers should be used to ensure that the test is conducted according to quality standards and regulations. Additionally, using stable materials is crucial, as their composition will not influence the equipment or leave residues.

At the beginning of each working day, the Bowie & Dick test should be performed to determine the correct operation of the autoclave.

The steps to follow are:

1. Ensure that the interior of the machine is empty.
2. Place the test near the drain (only one kit should be used per cycle, without introducing any other elements).
3. Initiate the corresponding program: complete sterilization at 134℃ and 2.1 atmospheres of pressure for 3 minutes and 30 seconds.
4. Once completed, verify the results: check if the color change on the paper is continuous and uniform or if there is any noticeable variation.

The result is obtained when the cycle ends and the color is checked. It is then compared with the validation sheet (control chart) included in each box.

The reading provides results even for unsatisfactory tests. If the color changes uniformly but is not the expected shade, it indicates that the steam is not fully saturated, even though the penetration was homogeneous.

If the test reveals an uneven tone, a defect is present that needs to be corrected. There are three independent causes that can occur simultaneously:

• Poor quality of the produced steam.
• Existence of leaks.
• Vacuum pump failures.

A poor result (as mentioned above) should be addressed by performing a second test. If this second test also results in failure, it indicates that the autoclave is not functioning correctly. In this case, it should not be used until the fault or malfunction is resolved. Given that the reasons and causes are varied, it is essential to have qualified personnel available to resolve any inconsistencies or doubts.

When should the Bowie & Dick test be performed?

It is recommended to perform this type of test periodically. In addition to the routine use outlined in the laboratory protocol, this test should also be conducted in the following scenarios:

• After any repair or maintenance operation, to ensure that the autoclave is operating correctly.
• If the autoclave has been out of use for an extended period.

Variations of the Bowie & Dick test: DART test

There are currently some variations of the Bowie & Dick test, the most popular being the DART test, which stands for Daily Air Removal Test. The application criteria for this test are outlined in ISO 11140-5:2007, Sterilization of health care products, Chemical indicators, Part 5: Class 2 indicators for Bowie & Dick type air removal tests. Known as the American version, the specifications for the package include that it is made of cotton and is conducted with cycles at 132℃ for 4 minutes.

 

The Helix test is an essential tool for ensuring the effectiveness of the sterilization process in autoclaves with fractionated pre-vacuum, widely used in hospitals and dental clinics. This test evaluates the autoclave’s ability to penetrate hollow instruments with steam, thereby guaranteeing the complete sterilization of devices with long cavities, such as laparoscopic instruments, orthopedic prostheses, and dental cannulas. The significance of this test lies in its ability to diagnose the proper functioning of the autoclave and prevent infections resulting from a loss of efficacy or equipment failure.

These tests typically consist of a kit of reactive strips, a reference color pattern, and a container composed of a tube and a threaded chamber, in which the reactive strip is inserted during the test.

What does the Helix test evaluate?

The Helix test is a functional test of the autoclave that evaluates the steam penetration capability in the chamber by monitoring two critical aspects of the sterilization process:

• Effectiveness of the initial pre-vacuum phase: Ensures that air is completely removed from the autoclave, allowing for proper steam penetration on all surfaces of hollow instruments.
• Sterilization conditions: Confirms that the necessary temperature and pressure of saturated steam are achieved during the sterilization phase.

These aspects are vital to ensure that instruments with cavities and complex geometries, commonly used in surgical procedures in traumatology, cardiology, and dentistry, are adequately sterilized, thereby minimizing the risk of infections for patients.

Procedure and operation of the Helix test

The procedure for conducting the Helix test is meticulous and must be followed rigorously:

1. Preparation of the autoclave: Before performing the Helix test, an initial vacuum cycle should be run with the autoclave empty to ensure that it is working properly.
2. Execution of the test: A chemical indicator strip is placed inside a capsule connected to a 1.5-meter tube, which simulates the cavity of a dental instrument. After closing the capsule, this assembly is placed inside the autoclave. It is important to close the capsule properly and avoid touching the ties securing the tube.
3. Sterilization process: The next step is to select the Helix Test program on the autoclave and run it. During the sterilization cycle, the autoclave must create a deep vacuum and allow steam to penetrate completely through the tube to reach the inside of the capsule.
4. Results and actions: At the end of the cycle, the capsule is removed, opened, and the color of the indicator strip is observed. If the test fails, it must be repeated. A second failure indicates the need to repair or replace the autoclave. In any case, it is recommended to keep a complete record of the test results to track the autoclave’s effectiveness over time.

As explained, to determine if the autoclave has passed the test, a color change in the indicator strip should be observed and compared with the pattern provided by the test manufacturer to confirm that the process was effective. If steam does not penetrate adequately, the strip will not change color or will change to an intermediate color, indicating a failure in the sterilization process.

When should the Helix test be performed?

The Helix test should be performed regularly to ensure optimal autoclave performance and safe sterilization procedures:

• Daily: Before starting to use the autoclave to sterilize instruments, to confirm that the autoclave is ready to operate properly.
• After repairs: Whenever maintenance or repairs are carried out on the autoclave, to verify that it continues to operate to the required standards.
• As part of routine checks: Following established guidelines, which recommend conducting vacuum and steam penetration tests regularly.

While any autoclave from any manufacturer is calibrated and checked at the factory, it is essential to periodically validate the correct functioning of pre-vacuum autoclaves used for clinical or surgical purposes through this test. This functional validation not only includes the Helix test but also other tests, such as the Bowie-Dick test. Additionally, each cycle should be accompanied by control tests such as spore tests or sterilization control tape.

Regularly performing this set of functional tests and controlling each cycle is fundamental for maintaining rigorous control over the sterilization process.

Importance of traceability

Performing the Helix test daily provides precise and timely information about the performance and effectiveness of a fractionated pre-vacuum autoclave. For this reason, it is recommended to keep an exhaustive record of the test results to monitor the autoclave’s efficacy over time and to promptly detect any malfunctions. This is crucial for preventing nosocomial infections in patients.

It is advisable to store both the indicator strip and the cycle report in a comprehensive log, which demonstrates rigorous control over the proper functioning of the autoclave. This detailed record not only complies with regulatory requirements in most countries but also provides an additional layer of security in clinical practice, protecting patients and ensuring the quality of sterilization procedures.