Asepsis and antisepsis in oral and maxillofacial surgery - sterilization, surgical infection, prophylaxis of wound and airborne infection, scrubbing up, operating field

Asepsis keeps pathogens out of the operative wound and the surgical site, and antisepsis applies agents to living tissue to stop microorganisms growing. Instruments are first cleaned, then sterilised by dry heat, moist heat in the autoclave, radiation, ethylene oxide or chemical means, and kept sterile until use. The surgical team scrubs and gloves, and the patient's skin and mouth are disinfected and covered with sterile drapes. The operating theatre is divided into zones to limit contamination. Surgical site infection and airborne infection are the two main risks to prevent, and antibiotic prophylaxis is used for selected wounds.

Asepsis and antisepsis are the two basic principles of infection control in surgery. They are related but not the same, and the terms below are used throughout this topic.

Asepsis is the set of methods that prevent contamination of wounds and other sites by making sure that only sterile objects and fluids come into contact with them. Medical asepsis tries to keep the patient, the health care staff and objects as free as possible of agents that cause infection. Surgical asepsis is the attempt to stop microbes gaining access to surgically created wounds.

Antisepsis is the procedure of applying an antiseptic solution, or an agent, that inhibits the growth of microorganisms while remaining in contact with them. Antiseptics are applied to living tissue, whereas disinfectants are used on inanimate objects.

Cleaning removes visible contamination but does not necessarily destroy microorganisms. It is a necessary first step before effective disinfection or sterilisation.

Sanitising reduces the microbial population on an object to a safe level.

Decontamination removes pathogenic microorganisms from an object so that it is safe to handle.

Disinfection is a process that reduces the number of viable microorganisms to an acceptable level. It eliminates defined pathogens, but not all microbial forms, and it may not inactivate some viruses and bacterial spores. The main difference from sterilisation is the lack of sporicidal activity. Disinfection is divided into three levels: high, intermediate and low. High-level disinfectants destroy all microbes except spores, intermediate-level disinfectants are active against all microbes apart from spores, and low-level disinfectants act only on some viruses and bacteria. Prions are not affected by disinfection. The table shows which organisms each level acts on, and the chart shows the same order of resistance.

Sterilisation destroys or removes all microorganisms from an article, surface or medium, including spores. Sterility is the freedom from viable forms of microorganisms. There are no degrees of sterility: an item is either sterile or it is not.

Dental instruments are classified as critical, semi-critical or non-critical, according to their risk of transmitting infection and therefore the need to sterilise them between uses. The category decides the level of processing that is required.

Critical instruments in the lecture photograph are surgical scissors, elevators and extraction forceps. Semi-critical instruments are a dental syringe, a probe and a mouth mirror. Non-critical items are a mixing spatula, a plastic bowl and plastic covers.

Sterilising any instrument needs three definite stages: presterilisation cleaning, the sterilisation process and aseptic storage. Cleaning comes first because organic matter, blood and saliva form a protective barrier that shields microorganisms and stops them being destroyed. Cleaning is done in one of three ways: manually, by ultrasound or by mechanical washing. Instruments are prepared by cleaning, disinfection and sterilisation, in that order, and disinfection of instruments is undertaken using an automated washing process once organic debris has been removed.

Manual cleaning is the simplest and cheapest method, but it is time consuming and difficult to achieve well. Heavy-duty gloves and glasses must be worn to protect against needle-stick injury and to protect the eyes. Soaps and detergents are the materials used.

In ultrasonic cleaning, electrical energy is converted into vibratory sound waves that pass through a soap solution containing the instrument. It is used mainly for burs, bone files, bone cutters, artery forceps and saws.

Mechanical washing uses high-pressure jets of water, with or without detergent, to remove debris from instruments. Small instruments such as burs and blades are not suitable for this type of cleaning.

Mucus and clotted blood may harbour bacteria and make it impossible for steam to reach them, so the first step in sterilisation is to scrub all instruments until clean with a brush under a running cold water tap. An ultrasonic bath gives a very high standard of cleanliness, especially for hinged instruments, suction tubes and suction heads. Cold water should be sucked through suction tubes and heads immediately after the operation is finished. Cleaning also includes stripping down, cleaning and oiling all working machinery, such as handpieces.

Dry heat is the most common and one of the most effective methods of sterilisation, and it is used mainly for glassware and bulky items that can withstand heat. Its advantages are ease of use and the unlikelihood of damaging heat-resistant instruments. It kills organisms by dehydration and oxidation, by protein denaturation and by the toxic effects of raised electrolyte levels. The factors that decide whether sterilisation by heat is achieved are the nature of the heat (dry or moist), the temperature and time, the number of organisms present, whether the organism forms spores, and the material from which the organisms must be removed.

Red heat sterilises metal objects by holding them in a flame until they are red hot. Examples are inoculating wires, needles and forceps. Flaming passes an article over a flame without letting it become red hot. Examples are glass plates, cotton wool plugs and glass slides.

A hot air oven sterilises items that are not damaged by high temperature. These include laboratory glass, flasks, instruments with sharp cutting edges, handles, dishes and mouth mirrors.

Sterilisation by dry heat is complete only when the temperature and time are both achieved throughout the load. The lecture gives these combinations.

A glass bead sterilizer uses glass beads, molten metal or salt as the medium, at 220 °C. Small instruments such as endodontic files, artery forceps, scissors and burs are submerged in the beads and are sterilised in 10 seconds, provided they are clean. The unit needs a warm-up time of at least 20 minutes to make sure the temperature is uniform.

Spores of a non-toxigenic strain of Bacillus subtilis and Clostridium tetani are used as the microbiological test of dry heat. A chemical indicator is also available in the form of a test strip, Browne's test strip, which changes colour when the conditions have been met.

Moist heat causes denaturation and coagulation of proteins. Water is a better medium than air for transferring heat, so moist heat kills organisms in less time than dry heat at the same temperature.

Pasteurisation uses either 63 °C for 30 minutes (the holder method) or 72 °C for 15 to 20 seconds (the flash method), followed by rapid cooling to 13 °C. It is used for heat-sensitive liquids and pharmaceutical products, not for instruments.

Tyndallisation is named after John Tyndall. The material is exposed to 100 °C for 20 minutes on three successive days. The first exposure kills all vegetative bacteria and spores. Spores that survive germinate in the favourable medium and are killed on the later exposures.

Steam is an effective means of sterilisation because of its high penetrating capacity and because it gives a large amount of heat to any surface it comes into contact with. The autoclave, or steam sterilizer, is the usual apparatus for sterilising instruments with steam. It works by creating steam and then, through a series of valves, increasing the pressure so that the steam becomes superheated.

An autoclave, or steam sterilizer, consists of the following parts.

1. A cylindrical or rectangular chamber, with a capacity of 400 to 800 litres.
2. A water heating or steam generating system.
3. Steam outlet and inlet valves.
4. Single or double doors with a locking mechanism.
5. A thermometer or temperature gauge.
6. Pressure gauges.

The diagram shows how the steam moves through the chamber and the steam jacket, and where the valves sit.

To achieve sterility, a holding time of at least 15 minutes at 121 °C (250 °F), or 3 minutes at 134 °C (273 °F), at 15 psi (100 kPa) above atmospheric pressure is required. Instruments must be packaged so that steam can flow freely around them, for example in sterilisation pouches or wrapped in cotton cloth. Crawford and Oldenburg recommended adding ammonia to the autoclave to avoid corrosion. Moist heat has a tendency to dull and rust instruments, and autoclaves are costly.

Three kinds of indicator check that the autoclave has worked.

• A physical indicator is an alloy designed to melt only after the relevant holding time has been reached.
• A chemical indicator is a strip or tape that changes colour once the correct conditions have been met.
• A biological indicator uses spores of Geobacillus stearothermophilus, the toughest organism for an autoclave to destroy. Its spores need an exposure of 15 minutes at 121 °C to be destroyed.

Radiation used for sterilisation is of two types, ionising and non-ionising. Both can be used to kill or inactivate microorganisms.

X-rays, gamma rays and cosmic rays are highly lethal to DNA and other vital constituents of cells. They have high penetration power. There is no appreciable rise in temperature, so this is referred to as cold sterilisation. Commercial plants use gamma radiation to sterilise plastics, syringes, swabs and catheters.

Two types of non-ionising radiation are used. Ultraviolet light is short-range UV, which is considered germicidal. At a wavelength of 2537 angstroms it destroys the DNA of microorganisms, and it is used mainly for purifying air and water in hospitals. Infrared light is most commonly used to purify air, for example in the operating room. It is effective, but it has no penetrating ability.

Ethylene oxide sterilisation is used almost exclusively for medical products that cannot be steam sterilised or that are sensitive to radiation. Ethylene oxide destroys microorganisms by alkylation and by causing denaturation of their nucleic acids. The conditions are 30 °C to 60 °C with a relative humidity above 30%, and a gas concentration of 200 to 800 mg/l for at least 3 hours. At 50 °C it is effective in killing all organisms, including spores, within 3 hours. The gas is usually mixed with carbon dioxide and nitrogen to make it safer.

Ethylene oxide diffuses readily through porous materials such as plastic and rubber. Its advantages are that it is effective for sterilising porous materials, large equipment, and materials sensitive to heat or moisture. Wrapped instruments are often sterilised this way, particularly plastic or metal instruments that are not heat resistant.

Its disadvantages are a lengthy cycle time, the cost, and potential hazards to patients and staff. It also needs special equipment, and equipment exposed to ethylene oxide must be aerated for 8 to 12 hours at 50 to 60 °C because the gas is highly toxic.

Chemical solutions are used as disinfectants and antiseptics. No available chemical solution will sterilise instruments that are only briefly immersed in it. There is also a risk of tissue damage if a residual solution is carried over into the wound while the instrument is being used. Most chemicals act in a non-specific and complex way, but most of them affect microorganisms by one of three mechanisms.

1. Cell membrane injury.
2. Coagulation and denaturation.
3. Interactions with the functional groups of proteins.

Hospital disinfectants are used for three purposes: disinfection of skin and mucous membranes, disinfection of instruments and other items, and decontamination of the inanimate environment.

The main groups of chemical agents are listed below, with the examples and key facts given in the lecture.

Alcohol at 70% to 75%, either ethyl or isopropyl, has a wide antibacterial activity and is the most active against TB. Phenolic compounds and hexachlorophene are used for their wide range of antibacterial activity.

The maintenance of sterility during transport and storage is of the utmost importance. Instruments are kept wrapped until they are ready for use, and sterile packs must be handled as little as possible to reduce the risk of contamination. Sterilised packs should be allowed to cool before storage, otherwise condensation forms inside the packs.

The store must be protected against pests such as rodents, ants and cockroaches. Materials should be stored at least 8 inches (about 20 cm) off the floor and 18 inches (about 46 cm) from the ceiling. Sterile packs are stored and issued in the correct date order, and are preferably kept in drums that can be locked. Preset trays and cassettes are useful, because the instruments can be organised as the procedure requires.

Instruments are sterilised in steel trays, or wrapped in drapes, which are placed either directly in the autoclave or in special metal containers with holes so that steam can pass through during sterilisation. After sterilisation the holes of the container are sealed, so that whatever the container holds remains sterile until it is used.

A package holding the full set of instruments for each surgical procedure is very practical. The sterilised instruments in it may be sealed and stored for a long period. A package that is opened and from which one or more instruments are removed repeatedly must be re-sterilised at least once a week.

There are three types of hand washing: social hand washing, clinical hand washing and surgical hand washing.

Surgical scrubbing aims to reduce resident and transient skin flora (bacteria) to a minimum. Proper hand scrubbing, together with sterile gloves and a sterile gown, gives the patient the best possible barrier against pathogenic bacteria in the environment and against bacteria from the surgical team.

Preparation begins with cleaning the hands with soap. Scrubbing should be restricted to critically contaminated areas, and alcoholic solutions or disinfectant soaps are used. The scrub takes about 3 to 5 minutes, and the washing order is the hands first, then the arms, the elbows and the wrists, and finally only the hands. No non-sterile area above the elbows should be touched during the procedure.

Before scrubbing, the arms are bared to the elbow, and all rings, watches and jewellery are removed. Fingernails must be kept short and free of polish so that they can be cleaned properly with a sterile scrubbing brush or nail scraper. The hands and forearms are washed under a running tap with a well-soaped antiseptic detergent solution, working from the fingertips up towards the elbow. The suds are rinsed off at intervals, always so that the water runs off at the elbow and not over the hands. The hands are dried on a sterile towel by wiping from the hands up towards the elbows.

Preoperative washing of the hands reduces the number of normal and transient flora on the hands, and it also inhibits the growth of bacteria under the glove during the procedure.

Before the operation the surgeon wears shoe covers, a cap covering the hair, a surgical mask and appropriate clothing. For minor procedures in dental surgery, gloves are worn. For extensive operations where there is a risk of infection of the staff and the theatre, a sterile gown and sterile gloves are worn. The dentist puts on a sterile gown, which the assistant ties, and then places the gloves. The first glove is held by its cuff in the right hand and placed on that hand.

Sterile technique has seven elements.

1. Minimising contamination of the wound.
2. Wearing scrubs and clogs.
3. Scrubbing up.
4. Sterile gowns and gloves.
5. Sterile instruments.
6. Preparing the operation site with antiseptic solution.
7. Avoiding contamination during surgery.

Preparation starts with a preoperative assessment, and any focal source of infection is treated before surgery. Swabs are also taken for MRSA. Pre-operative skin preparation is done with iodophors (povidone iodine or Braunol) and chlorhexidine. The solution is applied with a sponge from the area of the incision outwards.

Oral preparation follows the same logic. After the patient is seated in the dental chair, the assistant disinfects the area to be operated on. The skin around the mouth is first disinfected with gauze impregnated with antiseptic solution, and then the mucosa of the oral cavity is disinfected. The patient's mouth cannot be sterilised, and it is a source of infection. Preoperative scaling and good oral hygiene reduce the chance of gross contamination, and patients acquire immunity to their own oral flora.

Three sterile drapes, each about 80 by 80 cm, are required.

1. The first drape is placed on the upper part of the chair, covering the back and headrest, where the patient lies.
2. The second drape is folded into a triangle and placed on top of the first, where the patient rests the head. The base of the triangle faces downwards, covering the nape of the neck.
3. The lateral corners of the triangular drape cover the head and are fastened with a towel clamp at the base of the nose. The third corner is lifted forward over the scalp hair and fastened at the base of the nose with the same towel clamp.
4. The third drape is spread across the chest up to the neck and fastened to the sides of the triangular drape with two towel clamps. The nose, mouth and inferior border of the mandible are left exposed.

Sterile instruments, fluids and dressings are laid out on a trolley. Only the instruments on the trolley are used. If pre-packed instruments are not used, the instruments must be handled with sterile forceps. The surgeon and assistant wear sterile disposable gloves.

The principle of the antiseptic environment is to minimise bacterial contamination, especially near the operating table. The concept of zones is useful and must be employed. The operating area is divided into four zones.

• Outer and general access zonethe patient reception area and the general office.
• Clean or limited access zonethe area between reception and the general office, and the corridors and staff room.
• Restricted access zonefor properly clothed personnel engaged in operating theatre activities, including the anaesthetic room.
• Aseptic or operating zonethe operating theatre itself.

A third person should be present to adjust the operating lights and the position of the patient.

No procedure, however minor and particularly under general anaesthesia, should be attempted without a suction apparatus. The suction must be tested before the operation starts, and whenever possible an alternative form of suction should be available in case of breakdown. Electrical suction is very powerful but does occasionally fail. Suction from the water supply is very effective, simple, trouble-free and economical, and is ideally suited to dental surgery. Compressed air can also provide powerful suction. Whichever method is used, a catchment bottle must be included in the circuit, so that the bottle can be searched if roots are lost. A handwritten annotation under the compressed-air paragraph on the lecture slide reads 'forbidden in surgery'. The annotation is a student's handwriting, not the printed text, and it is not used as a rule here (see the handover).

Wounds are inspected or dressed by hands that are covered with fresh, clean gloves. The most common risk of infection is the transmission of disease through accidental needle pricks or scalpel lacerations. The risk is reduced by using a needle cap, by using a haemostat to hold the cover while resheathing the needle, and by never applying or removing a blade from a scalpel handle without an instrument. Used blades and needles are disposed of in specially designated areas for contaminated sharp objects.

Surgical infection is the main complication that the sterile technique in this topic is designed to prevent. The sub-notes below cover its definition, the classification of wounds, its causes, how it develops, how it presents, how it is diagnosed and managed, and its complications.

Sepsis is the breakdown of living tissue by the action of microorganisms, accompanied by inflammation. The mere presence of microorganisms does not constitute a septic state. Surgical infection, or wound sepsis, is infection of the operative wound after surgery.

Surgical wounds are classified by their level of contamination. A clean wound is one with no contamination of the oral cavity or other infected sites. A clean-contaminated wound is one in which the oral cavity or another normally colonised site is entered. Removal of impacted third molars is a clean-contaminated procedure. A contaminated wound has gross contamination, and a dirty wound already contains established infection at the time of surgery.

Infections complicating surgical outcomes usually result from gross bacterial contamination of susceptible wounds. Failure to follow aseptic technique is a frequent reason for virulent microorganisms to be introduced into the wound. Excessive tissue trauma, remaining necrotic tissue, foreign bodies and compromised host defences all make a wound more likely to become infected. Wound sepsis is related to the individual surgeon's technique, and the most important factor in minimising it is meticulous surgical technique. Patients with diabetes, on steroid therapy, after organ transplantation, with malignancy or on chemotherapy, with chronic renal disease or with malnutrition have compromised defences.

Continuing bacterial infection stimulates the host immune defences, which produce inflammatory mediators such as prostaglandins and thromboxane. Neutrophils migrating into the wound release cytotoxic enzymes and free oxygen radicals. Thrombosis and vasoconstrictive metabolites cause hypoxia of the wound, which lets bacteria multiply and tissue damage continue. Bacteria destroyed by host defences release neutrophil proteases and endotoxins. Newly formed cells and their collagen matrix are vulnerable to these breakdown products, so cell and collagen lysis impairs healing.

Inadequate tissue perfusion and oxygenation of the wound further compromise healing, allowing bacteria to proliferate and establish infection. Devitalised tissue and foreign bodies in a healing wound act as a haven for bacteria and shield them from the body's defences. A haematoma, which is a collection of blood or serum at the wound site, provides an ideal medium for the growth of microorganisms.

The classic signs and symptoms of local infection are erythema, warmth, swelling, pain, and an accompanying odour and pus. Impaired healing is seen. Partial or total separation of the wound margins, called wound dehiscence, may appear within the first week after surgery. Most dehiscence results from tissue failure rather than from improper suturing technique.

Clinical diagnosis is made from the classic signs of local infection.

Paraclinical diagnosis uses culture and sensitivity testing, which is used routinely in patients with immunocompromising systemic disease. Growth of the organisms is slow, and results may not be available until the third day of therapy.

Differential diagnosis includes alveolar osteitis (dry socket), haematoma and wound dehiscence, which can produce pain and swelling without pus.

Surgical technique is the most important factor in controlling wound sepsis. Debridement, which removes dead and devitalised tissue and any foreign material, reduces the number of microbes, toxins and other substances that inhibit healing. A drain or a pressure dressing can be used postoperatively to eliminate dead space. Incision and surgical drainage are used for an established collection of pus. Antibiotic choice follows the principles for odontogenic infection: penicillin is the main choice, followed by clindamycin, cephalosporins and metronidazole.

Complications include wound dehiscence, spread of infection to the surrounding tissues, and the formation of abscesses or phlegmons. Prevention is by good surgical technique and, when indicated, by antibiotic prophylaxis, which is described in the next section.

Prophylaxis rests on two measures: good surgical technique, which is the first defence, and antibiotic prophylaxis for selected wounds only.

Good surgical technique reduces wound sepsis. The points to observe are careful handling of tissues; removal of all foreign bodies and dead tissue; avoidance of excess diathermy and sutures; avoidance of excessive suture tension; accurate placement of sutures; and avoidance of haematoma formation. Monofilament sutures are associated with less wound sepsis than braided suture materials. A surgeon should keep a close audit of their own infection rates and compare them with those of another surgeon, because this comparison can lead to a steady reduction in infection. Infection rates that are unacceptably high must be addressed.

Prophylactic antibiotics reduce wound sepsis in clean-contaminated and contaminated wounds. Antibiotic use in a clean wound has no purpose on its own, but it should be given if foreign material is inserted or if the patient has cardiovascular disease. The ideal prophylactic agent is bactericidal, non-toxic and inexpensive, and is active in vitro against the common organisms that cause wound infection after the specific procedure. Because antimicrobial resistance is increasing, prophylaxis should not be overused.

Perioperative antimicrobial prophylaxis is recommended for operative procedures with a high rate of postoperative wound infection, for operations in which foreign material is implanted, and for those in which a wound infection would have disastrous results.

The prophylactic agent is given 30 to 60 minutes before surgery. It is common practice to give the intravenous agent at the time of anaesthetic induction. There is no benefit in starting intravenous antimicrobial therapy before the perioperative period. A therapeutic concentration of the agent must be present in the tissue throughout the time the wound is open. For prolonged procedures, or for agents with short half-lives, an additional dose is given during the operation. The duration of prophylaxis is one or two postoperative doses. Prolonged prophylaxis is discouraged because of antimicrobial toxicity, the selection of resistant organisms and unnecessary expense.

Peterson's Principles of Oral and Maxillofacial Surgery gives an infection rate of about 1% to 5% for a competent, experienced surgeon after third molar surgery.

Airborne infection is spread by exhaled aerosols and droplets. The main airborne risk in the oral and maxillofacial setting is tuberculosis.

Tuberculosis (TB) is caused by Mycobacterium tuberculosis, an acid-fast bacillus, and it is the most common mycobacterial organism. Newer strains are resistant to drugs previously used against TB, and to some chemical disinfectants. Oral involvement from TB is rare and most often occurs secondary to pulmonary disease, according to Peterson's Principles.

Droplets produced during breathing, coughing, sneezing and speaking are the main route, through exhaled aerosols that carry M. tuberculosis bacilli from the infected lungs of one person to the lungs of another. Transmission can also occur through inadequately sterilised instruments. The organism is sensitive to heat, irradiation and ethylene oxide, and it is not highly contagious.

Oral TB lesions appear as ulcers, fissures, swellings or gingival enlargement. Primary lesions are less common and usually involve the gingiva, the mucobuccal vestibule or extraction sites. Secondary lesions are more common and are reported on the palate, buccal mucosa, lip, gingiva, tongue, retromolar area and floor of the mouth. Salivary glands and cervical lymph nodes are also involved.

Early diagnosis of oral TB is by biopsy.

Protect doctors and nurses by TB skin testing, and by staff wearing N95 facemasks. Instruments must be sterilised correctly, because the organism is sensitive to heat, irradiation and ethylene oxide. Operating room ventilation, sterilisation, barriers and surgical technique have together helped to reduce surgical site infection.

Secondary oral lesions are reported in the salivary glands and in the cervical lymph nodes.