Hospitals aim to provide a safe environment for patient care and treatment. However, they can become dangerous when infections and contaminants spread easily between patients, medical instruments, and staff. As many hospital procedures involve direct contact between medical tools or surgical instruments and a patient’s tissues, blood, or mucous membranes, the risk of cross-infection between patients is significant. Nevertheless, hospital-acquired infections can be effectively prevented and managed through sterilization and disinfection techniques. This article will explore various sterilization of medical equipment methods, particularly techniques such as the use of ethylene oxide gas and aldehydes.
What Does Sterilization Mean?
Sterilization refers to the process that eliminates or deactivates all microorganisms, including fungi, bacteria, spores, and unicellular organisms, as well as biological agents like prions, from a surface using physical or chemical methods.
This process is critical for medical equipment to minimize the risk of infection transmission from one patient to another. Therefore, sterilization and disinfection are essential for hospitals, clinics, laboratories, and other medical institutions, and they are regulated by specific standards and authorities.
Types of Sterilization of Medical Equipment
Sterilization methods can be divided into three main categories: thermal, chemical, and radiation. Medical instruments are made from various materials, such as metal, ceramic, glass, and plastic, each requiring a sterilization method that preserves the physical and chemical integrity of the material. Common sterilization techniques include:
- Thermal Methods
- Chemical Methods
- Radiation Methods
Chemical Sterilization Methods
Chemical sterilization methods are widely used in healthcare settings to eliminate microorganisms on medical equipment and surfaces, especially those that may be damaged by heat or radiation.
These methods involve the use of chemical agents, such as ethylene oxide gas, aldehydes, hydrogen peroxide, and peracetic acid, to destroy bacteria, viruses, fungi, and spores. Each chemical agent has specific properties, making it suitable for different types of equipment and sterilization needs.
1-Ethylene Oxide Gas Sterilization
Sterilization using ethylene oxide (EO) gas is a widely used technique that manufacturers rely on to ensure medical equipment safety. For many products, ethylene oxide sterilization is the only effective method that doesn’t compromise the equipment’s integrity during the process.
What Is Ethylene Oxide, and How Does It Work?
Ethylene oxide is a colorless gas that is toxic to cellular proteins and nucleic acids, particularly in microorganisms and spores. Its sterilizing effect mainly results from its ability to alkylate amino groups in microbial nucleic acids, rendering them inactive.
Ethylene oxide sterilization is suitable for medical devices made from certain polymers, metals, or glass, as well as items with multiple layers of packaging. Examples range from general healthcare tools, such as wound dressings, to more specialized devices like stents for specific body treatments. This method is particularly valuable for sterilizing heat- or moisture-sensitive medical equipment.
Benefits of Ethylene Oxide Gas Sterilization
- Low-temperature processing: Suitable for heat-sensitive items.
- Compatibility with various materials: Usable for plastics, metals, glass, and rubber.
- High chamber capacity: Allows for processing large quantities.
- High penetration: Capable of sterilizing complex and internal areas of equipment.
- Extended shelf life of sterilized items: Increases the longevity of medical devices.
Drawbacks of Ethylene Oxide Gas Sterilization
- Long cycle times, often exceeding 14 hours.
- High flammability, requiring careful handling.
- Toxic and potentially carcinogenic, posing a risk to users.
- Residual toxicity, leaving possible toxic residues on tubing and surgical instruments.
- Specialized facility requirements, such as dedicated rooms and ventilation systems.
- High maintenance needs, including annual servicing and the use of consumable supplies.
2-Using Aldehydes for Sterilization
Another group of compounds used for sterilization are aldehydes, which contain the functional group -CHO. Aldehydes form as a result of the oxidation of primary alcohols, where the carbonyl group is bonded to at least one hydrogen atom.
Currently, two aldehyde compounds—glutaraldehyde and formaldehyde— are commonly used as disinfectants due to their effective antimicrobial properties.
What is Glutaraldehyde, and What are Its Uses?
Glutaraldehyde is one of the most widely used disinfectants globally, with applications across various fields. It is highly reactive and interacts strongly with bacterial cell walls, giving it a potent antimicrobial effect against bacteria, fungi, and viruses.
While it does not corrode plastics, metals, or lenses, glutaraldehyde, like other aldehydes, is toxic, irritating, and can trigger allergies. Its vapors can irritate the mucous membranes of the nose, throat, and eyes and may affect the respiratory system, causing coughing and bronchial spasms, especially in people with asthma. Due to these safety concerns, its use is restricted or banned in some countries.
What is Formaldehyde, and What are Its Uses?
Formaldehyde can be used as a disinfectant in both liquid and vapor forms. It has a broad antimicrobial range, effectively killing bacteria, bacterial spores, fungi, and many viruses (though its bactericidal action is slower than glutaraldehyde). While this method is reliable, it poses a risk of leaving toxic residues on medical equipment, which could be harmful to operators.
The advantages of formaldehyde include its relatively low cost and the immediate usability of sterilized items after processing. However, its drawbacks include toxicity, a lengthy sterilization cycle, and the fact that inhaling formaldehyde vapor has been shown to be carcinogenic to humans, according to the UK’s Health and Safety Executive.
3-Using Peracetic Acid for Sterilization
Peracetic acid (PAA) is an organic compound with the formula CH₃CO₃H and can be used in both liquid and vapor forms. Both liquid peracetic acid and vaporized peracetic acid (VPA) are potent disinfectants that eliminate surface contaminants. Peracetic acid can also be applied to heavily contaminated or infected wounds to reduce microbial load on dressings. Although limited information is available on its precise mechanism, it is believed that, like other oxidizing agents, peracetic acid disrupts cellular structure by altering proteins, affecting cell wall permeability, and oxidizing sulfur bonds in proteins, enzymes, and other metabolites.
Extensive testing on over 100 different materials has shown that VPA is highly compatible with a variety of substances. Products that are generally unsuitable for sterilization with liquid chemicals can be safely sterilized using the VPA method. This method has been successfully tested on thermoplastics, thermosets, adhesives, batteries, and bioresorbable materials, demonstrating a high level of compatibility.
Moreover, VPA is administered as a vapor at room temperature, allowing it to sterilize items without the need for heat, which can damage heat-sensitive materials. The process takes between two to four hours, after which VPA decomposes into water, oxygen, and carbon dioxide, eliminating the need for external ventilation and posing no carcinogenic risk.