Various types of sterilizers and sterilization techniques used in hospitals

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Sterilization is a critical process in hospitals and healthcare settings to prevent the transmission of infections and ensure patient safety. There are various types of sterilizers and sterilization techniques used in healthcare facilities, each with its own advantages and limitations. In this comprehensive guide, we will explore the various methods of sterilization, the equipment and technologies involved, and the factors that influence the choice of sterilization method in hospital settings.

Hospitals and healthcare facilities use various sterilization techniques to ensure that medical instruments, devices, and equipment are free of harmful microorganisms. Sterilization is applied to surgical instruments, reusable medical devices, laboratory equipment, and even the surfaces in clinical environments. The choice of sterilization method depends on the type of material being sterilized, the desired level of sterility, and other factors.

Types of Sterilization

Sterilization techniques can be broadly categorized into the following types:

  1. Heat-Based Sterilization:
    • Autoclaving: Autoclaving is one of the most common methods of sterilization in healthcare settings. It involves the use of high-pressure steam at temperatures above 121°C (250°F). The high temperature and pressure effectively kill microorganisms and spores. Autoclaves are suitable for sterilizing a wide range of materials, including surgical instruments, glassware, and laboratory equipment.
    • Dry Heat Sterilization: Dry heat sterilization is less common but can be used for materials that are sensitive to moisture. It involves the use of hot air at temperatures between 160°C to 190°C (320°F to 375°F) for an extended period. This method is often used for sterilizing glassware and certain powders.
    • Hot Air Sterilization: Hot air sterilization is similar to dry heat sterilization but is typically conducted at lower temperatures (160°C to 180°C). It is suitable for materials that are sensitive to high temperatures and can be used for items such as glassware and some plastic materials.
  2. Chemical Sterilization:
    • Ethylene Oxide (ETO) Sterilization: Ethylene oxide is a gas that is highly effective in sterilizing a wide range of materials, including plastics, rubber, and heat-sensitive equipment. It is often used for items that cannot withstand the high temperatures of autoclaving. ETO sterilization is performed in dedicated chambers, and aeration is required to remove residual gas.
    • Glutaraldehyde Sterilization: Glutaraldehyde is a liquid chemical sterilant used for heat-sensitive equipment, such as endoscopes. It requires a longer exposure time than autoclaving or ETO sterilization and is often used in conjunction with an automated system to monitor and control the process.
    • Hydrogen Peroxide Plasma Sterilization: Hydrogen peroxide plasma sterilization is a low-temperature method that utilizes hydrogen peroxide gas plasma to sterilize a variety of materials, including heat-sensitive devices. It is effective and safe, making it suitable for delicate instruments and electronic components.
  3. Radiation-Based Sterilization:
    • Gamma Irradiation: Gamma irradiation uses high-energy gamma rays to sterilize materials. It is often used for disposable medical supplies, such as syringes and packaging. Gamma irradiation is highly effective but requires specialized facilities.
    • Electron Beam Sterilization: Electron beam sterilization is similar to gamma irradiation but uses accelerated electrons to achieve sterilization. It is also used for disposable medical supplies and materials that are sensitive to radiation.
  4. Filtration Sterilization: Filtration is a technique that involves passing liquids or gases through a filter with pore sizes small enough to retain microorganisms. This method is commonly used for sterilizing heat-sensitive liquids, such as culture media and some pharmaceuticals.
  5. Low-Temperature Sterilization:
    • Steam Formaldehyde Sterilization: Steam formaldehyde sterilization is a low-temperature method used for items that cannot withstand high heat. It combines steam and formaldehyde to achieve sterilization. The process requires longer cycle times and aeration to remove residual formaldehyde.
    • Ozone Sterilization: Ozone sterilization is a low-temperature method that uses ozone gas to kill microorganisms. It is mainly used for sterilizing medical equipment, textiles, and certain laboratory items.
  6. Miscellaneous Sterilization Techniques: There are other less common sterilization techniques, such as microwave sterilization, silver ion sterilization, and supercritical carbon dioxide sterilization. These methods are used in specific applications and are less prevalent in healthcare settings.


General Principles: Steam is an effective sterilant for two reasons. First, saturated steam is an extremely effective “carrier” of thermal energy. It is many times more effective in conveying this type of energy to the item than is hot (dry) air. In a kitchen, potatoes can be cooked in a few minutes in a steam pressure cooker while cooking may take an hour or more in a hot-air oven, even though the oven is operated at a much higher temperature. Steam, especially under pressure, carries thermal energy to the potatoes very quickly, while hot air does so very slowly.

Second, steam is an effective sterilant because any resistant, protective outer layer of the microorganisms can be softened by the steam, allowing coagulation (similar to cooking an egg white) of the sensitive inner portions of the microorganism. Certain types of contaminants, however, especially greasy or oily materials, can protect microorganisms against the effects of steam, thus hindering the process of sterilization. This reemphasizes the need for thorough cleaning of objects before sterilization.

Requirements: Steam sterilization requires four conditions: adequate contact, sufficiently high temperature, correct time and sufficient moisture. Although all are necessary for sterilization to take place, sterilization failures in clinics and hospitals are most often caused by lack of steam contact or failure to attain adequate temperature.

Instructions Use for Steam Sterilization

  1. Decontaminate, clean and dry all instruments and other items to be sterilized.
  2. All jointed instruments should be in the opened or unlocked position, while instruments composed of more than one part or sliding parts should be disassembled.
  3. Instruments should not be held tightly together by rubber bands or any other means that will prevent steam contact with all surfaces.
  4. Arrange packs in the chamber to allow free circulation and penetration of steam to all surfaces.
  5. When using a steam sterilizer, it is best to wrap clean instruments or other clean items in a double thickness of muslin or newsprint. (Unwrapped instruments must be used immediately after removal from the sterilizer, unless kept in a covered, sterile container.)
  6. Sterilize at 121qC (250qF) for 30 minutes for wrapped items, 20 minutes for unwrapped items; time with a clock.
  7. Wait 20 to 30 minutes (or until the pressure gauge reads zero) to permit the sterilizer to cool sufficiently. Then open the lid or door to allow steam to escape. Allow instrument packs to dry completely before removal, which may take up to 30 minutes. (Wet packs act like a wick drawing in bacteria, viruses and fungi from the environment.) Wrapped instrument packs are considered unacceptable if there are water droplets or visible moisture on the package exterior when they are removed from the steam sterilizer chamber. If using rigid containers (e.g., drums), close the gaskets.
  8. To prevent condensation, when removing the packs from the chamber, place sterile trays and packs on a surface padded with paper or fabric.
  9. After sterilizing, items wrapped in cloth or paper are considered sterile as long as the pack remains clean, dry (including no water stains) and intact. Unwrapped items must be used immediately or stored in covered, sterile containers.

Factors Influencing Sterilization Method Selection

The choice of sterilization method in hospitals is influenced by several key factors:

  • Material Compatibility: Different materials may react differently to various sterilization methods. For example, some plastics may not withstand high-temperature autoclaving, and certain delicate instruments may be sensitive to chemical sterilants. The material composition and properties play a significant role in method selection.
  • Sterilization Efficacy: The desired level of sterility varies depending on the application. Some procedures require a high level of sterility to prevent infection, while others may have lower requirements. The chosen sterilization method must be effective in achieving the required level of sterility.
  • Equipment Availability: The hospital’s existing equipment and infrastructure may limit the choice of sterilization methods. For example, if a hospital lacks the facilities and equipment for gamma irradiation, it may not be a feasible option. Availability and access to specific sterilization methods are crucial considerations.
  • Cost: The cost of sterilization methods can vary significantly. Autoclaving, for instance, is cost-effective, whereas gamma irradiation and ethylene oxide sterilization can be more expensive due to the specialized equipment and facilities required. Hospitals must consider their budget when choosing a sterilization method.
  • Cycle Time: Some sterilization methods may have longer cycle times than others. For hospitals with high patient throughput, reducing equipment downtime is crucial. Faster methods like autoclaving are preferred in such cases.
  • Regulatory Compliance: Regulatory agencies, such as the Food and Drug Administration (FDA) in the United States, have specific requirements for the sterilization of medical devices. Hospitals must ensure that the chosen sterilization method complies with these regulations and standards.
  • Safety: The safety of patients and healthcare workers is of paramount importance. Some sterilization methods involve the use of hazardous chemicals or radiation, which can pose risks. Hospitals must implement safety measures and training to minimize these risks.

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Sterilization Equipment

Hospitals use various types of sterilization equipment to implement different sterilization methods. These include:

  • Autoclaves: Autoclaves are common in hospitals and use high-pressure steam for sterilization. They come in various sizes and configurations, including tabletop autoclaves for smaller instruments and large autoclaves for bulk sterilization of equipment.
  • Sterilization Cabinets: Sterilization cabinets are often used for small, heat-sensitive items. They use dry heat or other methods to sterilize items in a controlled environment.
  • Ethylene Oxide Sterilizers: Ethylene oxide sterilizers are specialized chambers that use ethylene oxide gas to sterilize a wide range of materials. They require aeration to remove residual gas.
  • Hydrogen Peroxide Plasma Sterilizers: These machines use hydrogen peroxide gas plasma to sterilize heat-sensitive equipment. They are known for their efficacy and safety.
  • Gamma Irradiation Facilities: Gamma irradiation facilities use high-energy gamma rays to sterilize items. These facilities are typically external to the hospital and receive materials for sterilization. They are commonly used for disposable medical supplies.

Quality Assurance and Sterilization Monitoring

To ensure the reliability of the sterilization process, hospitals must implement quality assurance measures and monitoring practices:

  • Record Keeping: Detailed records of each sterilization cycle, including process parameters, cycle time, and results, should be maintained for quality control and auditing purposes.
  • Routine Equipment Maintenance: Regular maintenance and calibration of sterilization equipment are essential to ensure consistent performance. Malfunctioning equipment can compromise the sterilization process.
  • Training and Competency: Healthcare workers responsible for sterilization must receive proper training in the use of sterilization equipment and adherence to protocols. Competency assessments should be conducted to ensure their proficiency.
  • Quality Control: Quality control processes should be in place to verify that the sterilization process consistently meets defined standards and that any deviations are promptly addressed.

Challenges and Innovations in Sterilization

  • Antibiotic-Resistant Microorganisms: The rise of antibiotic-resistant microorganisms poses a significant challenge in sterilization. Hospitals must ensure that their sterilization methods are effective against these resilient strains.
  • Sterilization of Complex Medical Devices: Modern medical devices can be complex, with intricate designs and multiple components. Sterilizing such devices without causing damage or affecting functionality is a complex task.
  • Emerging Sterilization Technologies: Ongoing research and development are leading to the emergence of innovative sterilization technologies, such as using cold plasma and advanced filtration methods. These technologies may offer improved sterilization options in the future.


Sterilization is a critical aspect of healthcare that directly impacts patient safety. Hospitals employ a range of sterilization techniques, each with its own advantages and limitations, to ensure that medical equipment and instruments are free of harmful microorganisms. The choice of sterilization method is influenced by material compatibility, sterilization efficacy, equipment availability, cost, cycle time, regulatory compliance, and safety considerations. Hospitals must also follow rigorous processes for cleaning, packaging, and validation, and establish quality assurance measures to maintain the integrity of their sterilization practices.

As the healthcare industry continues to evolve, addressing challenges like antibiotic resistance and complex medical devices, and exploring emerging sterilization technologies, will be crucial to maintaining high standards of patient care.


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  • American Association of Operating Room Nurses (AORN). 1992. Recommended practices: Sanitation in the surgical practice setting. AORN J 56(6): 1089–1095.
  • Association for Practitioners in Infection Control (APIC). 2002. APIC Text of Infection Control and Epidemiology on CD-ROM. APIC: Washington, DC.
  • Centers for Disease Control and Prevention (CDC). 2002. Questions and answers regarding Creutzfeldt-Jakob disease infection-control practices. Available at: (http//

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