What makes a product sterile? Only two decades ago, hospital and medical personnel cleaned and sterilized most items used in the practice of medicine. Today, preprepared medicinals and devices and the use of disposables have revolutionized this practice and ushered in a new age in medical care throughout the world. Responsibility for sterilization has largely shifted from the users of medical materials to the manufacturers. What are the consequences-and reasons-for what amounts to a massive change in the practice and technology of medicine? Have there indeed been permanent gains in medical care, or have we merely shifted the burden of sterilization from one group, hospitals, to another, manufacturers? And, in an era conscious of waste disposal and wise usage of resources, what does the patient gain by the shift to one-time use, disposable sterile products? As nurses, you know that none of these changes in systems of health care has occurred without reason. The new technology of sterilization assures physicians and nurses of more successful treatment and provides an extra measure of confidence that the products are indeed sterile for the ultimate benefit of the patient. How sterility is accomplished on these 200 billion medical products used annually, particularly medical devices, is best told through descriptions of methodologies employed by firms that produce sterile items. The practical provision of sterile products requires a highly reliable process at minimum cost to the user. Assurances that products are sterile are based upon minimizing the
possibility that contaminating organisms might survive a sterilization cycle. A typical program of contamination control comprises eight elements, with management policy and quality control as the single most important element of the overall effort. The seven other major elements are: employee selection and training, health and hygiene, new product design, facility design, containment equipment, manufacturing procedures, and control of raw materials. Testing of all elements is another essential for the success of the total control program. The quality control organization of a plant directs the sterility effort and is conscious of how contamination occurs and how it can be prevented. Its strategy includes manuals, directives, guidelines, and emphasis on presterilization, with an observance of sanitation so strict that many of the products may be sterile prior to sterilization. The presterilization procedures provide a more favorable environment for the actual sterilization process. The purpose is to govern microbial populations and to eliminate contaminants in advance-thereby increasing the confidence that the final product will be sterile. Raw materials are stored in areas that do not create contamination. Employees must be free of communicable disease and adhere to rigid health and hygiene practices. This means wearing lint-free clothes and hair covers (in some cases isolation suits), special shoes, and (when the product is touched) gloves; observing handwashing practices; and developing an awareness of where the hands have been and what they are going to touch next. Products, machinery, and facilities are designed to be easily cleaned and to reduce risk of contamination. Design features that
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might trap contaminants are avoided. Depending on their use, materials may be tested for toxicity, pyrogenicity, tissue compatibility, and suitability for long-term implantation. Exhaustive tests are made with highly resistant microorganisms to assure that crevices and hard-to-clean areas can be rendered sterile. The test microorganisms must be destroyed. Facilities are designed with barriers, either complete or partial (such as a laminar airflow bench), to keep out contamination and traffic. Transitional areas in which people or mater.ials pass back and forth may include change rooms, airlocks with germicidal ultraviolet, pass boxes, and double-door sterilizers. Consideration is given to air balance and air filtration and other services such as vacuum, gas, and water. Procedures are similarly designed for control of contamination. So advanced has the medical products industry become in techniques to control contamination that when the National Aeronautics and Space Administration needed to manufacture perfectly sterile components for lunar probes, techniques perfected in this industry were adapted. All this precedes the actual sterilization process. The selection of the best sterilization technique is based on two factors regarded as most important-materials compatibility and cycle reliability. It is in these areas that the industrial manufacturer with years of experience in selecting the right technique for his particular product inevitably has advantages over hospital staff. The sterilization method may be steam autoclave (moist heat), dry heat, radiation, or ethylene oxide (ETO) gas (gas sterilization). The method selected is that which prevents damage or deterioration of the product. For example, gas sterilization would be preferable for a plastic that becomes distorted or discolored at autoclave temperatures or that undergoes breakdown of physical properties if irradiated. Regardless of the sterilization method to be used, extensive laboratory tests are conducted before approval for production use. These tests include a thorough evaluation of both the sterilization effectiveness and any effects the sterilant may have on the products or packaging. Biological indicators (microorganisms with a known level of resistance to a certain 976
sterilization cycle) are used as checks. Complete destruction of highly resistant organisms such as Bacillus subtilis spores means that adequate safeguards have been taken to destroy other natural contaminants. Dry heat sterilization, perhaps the rarest in manufacturing facilities, involves exposure in a conventional hot-air oven. Since dry heat kills microbes by oxidation, the chamber must be controlled and monitored for time and temperature relationships to insure sterility. The moisture content is also controlled for certain items where it is necessary to maintain product stability. The most common sterilization method in hospitals and clinics because of economy of operation is the steam autoclave. It is often used in industry when temperature and moisture do not adversely affect the products or packaging. Manufacturing controls on the production autoclave include temperature, pressure, cycling time, air elimination, and saturation level, all of which may be monitored both by the unit's built-in indicators and by external monitoring systems of laboratory accuracy. One type of process indicator is the pellet-in-glass tube sterilizer control. By melting only when required temperatures are attained and maintained for certain times, this type monitor can detect most steamsterilizer problems. The plumbing system of a production autoclave is also routinely checked for contamination, leaks, or rust, and the water mineral content may be monitored in certain geographical areas where it is necessary. Sterilization by radiation, in use for over a decade in several European countries, is gradually becoming more competitive with other methods in the United States and is mainly for temperature-sensitive plastics. There are two basic methods of irradiation: high voltage electron beam from a linear accelerator or gamma radiation, which involves bombardment by cobalt 60 ions. The primary control, other than the general tests mentioned earlier, is to insure that the products receive a dosage that is both uniform throughout the lot and sufficient to insure sterilization. The established dosage is monitored by dosimeters placed at strategic locations in the lot. Other controls consist mainly of shielding and automated handling for the protection of operating room personnel from overexposure to the radiation.
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The current technology for ethylene oxide gas sterilization was developed to meet the requirements to sterilize heat-sensitive materials at temperatures and pressures that will not harm the product. While effective, the equipment must be operated with care and precision. In setting up an ETO sterilizer, manufacturers carefully test the chamber and its support apparatus for any gas leaks. The accuracy of all settings and monitors for temperatures, relative humidity, pressure, vacuum, and cycling time for the gassing and airwash cycles must be calibrated carefully. To assure proper functioning, the chamber is checked for areas where the relative humidity and gas concentrations or both are insufficiently high or dangerously low. This is done by placing precontaminated graded biological indicators at various locations, then testing for the kill-level on these spores. In addition to the chamber controls, a preconditioning area is usually set up to allow the lot or “retort” to reach certain parameters of temperature and humidity before being sterilized in the chamber. This preconditioning helps to insure the effectiveness of the ETO cycle, although it does not preclude the necessity for a humidification stage within the chamber during the sterilization cycle. Only after all the tests have been conducted and control parameters established is the chamber released for production. If at any time one or more of the critical control values must be changed, the cycle effectiveness must be recertified before use. Concern is frequently expressed about gas residues in products sterilized by ethylene oxide. Although this has been more of a problem in hospital resterilization of medical products, a few points should be emphasized. The packaging material for ethylene oxide sterilization, both paper and polyethylene-type pouches, is designed to be permeable to sterilant gases, air, and moisture vapor to permit sterilization, but must not be permeable to solids such as dust or microorganisms. Positive or negative pressure (vacuum) speeds this permeation, so manufacturers use several vacuum-degassing steps after the positive gas cycle to remove the greater percentage of gas from the packages. Products are continually aerating during the sterility test incubation period and during the entire time until the package is
opened for use. Certain materials which have a greater tendency to hold ETO residues, or which contain elements that interact with ETO to form its by-products (ethylene glycol or ethylene chlorohydrin), are subjected to special heated aeration cycles or held for longer periods before stocking. Through these controls and special care, manufacturers are able to insure that the residuals are far below the toxic level prior to shipment to customers. In the medical device industry, a product is sent to a fenced quarantine area for ten days after sterilization. During this time, samples and biological indicators from each lot are subjected to sterility testing. Finally, the product is pronounced acceptable, or rejected if data is not within specifications or if any uncertainty exists regarding the product’s sterility. Certification of sterility by the plant’s chief microbiologist releases the product for sale. The extensive precautions taken to guard the sterile integrity of medical products are not futile exercises. Both the safety of the hospital patient and the ethics of industry professionals demand that these controls be carried out. Government is providing further assurance through standards designed to regulate the manufacture and distribution of sterile medical materials. Users of sterile products have assumed a responsibility to transmit information about criteria and requirements to the manufacturer and to use the products properly in the correct manner. The concentrated efforts of research, management, engineering, and quality control all stand behind the product labeled “sterile” on delivery from a manufacturer to a hospital. From then on, it is up to you, the operating room nurse, and your colleagues in supply and distribution. On hospital shelves, stock should be properly rotated for proper inventory management; delivery systems must move products without violating their sterile packaging; and, finally, your skill and training assure that the product is properly removed from its package and put into use. Thus sterilization is achieved, retained, and delivered-with each step as essential as the one before.
Harold 0 Buzzell, President Health Industry Manufacturers Association
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