CLASSIFICATION OF SURGICAL SITE INFECTION

Classification of Surgical Site Infection

1.      Superficial incisional SSI: It occurs within 30 days after the operative procedure and involves only skin and subcutaneous tissue. This is again subdivided in to

·         superficial incisional Primary SSI and

·         superficial incisional Secondary SSI

2.      Deep incisional SSI: It occurs within 30 days after the operative procedure if no implant is left in place or within one year if implant is in place and the infection appears to be related to the operative procedure and involves deep soft tissues of the incision.

There are two types of deep incisional surgical site infection.

·         Deep Incisional Primary , and

·         Deep Incisional Secondary

3.      Organ / Space SSI:  occurs within 30 days after the operative procedure if no implant is left in place or within one year if implant is in place and the infection appears to be related to the operative procedure and infection involves any part of the body, excluding the skin incision, fascia, or muscle layers, that is opened or manipulated during the operative procedure.

Causes of surgical site infection

Wounds are able to heal despite the presence of quite large number of bacteria. Pathogens that cause SSI are acquired either endogenously from patient’s own flora or exogenously from contact with operating room personnel or the environment. The four main sources that require to be addressed to prevent SSI are personnel, equipment, the environment, and patient’s risk factors which interact in a complex way to foster the development of infection.

Endogenous factors

Predisposing factors

Host’s intrinsic ability to defend itself against microbial invasion, is an important determinant of the risk of infection following surgery. Extreme age, obesity, malnutrition, smoking, other immunosuppressive conditions like diabetes mellitus, malignancy, chronic lung diseases and, renal failure etc lead to impaired host defense mechanisms, and thus increase the risk for post operative wound infection. Low albumin, malnutrition, recent weight loss, immunosuppressive therapies are all contributing factors. Diabetes Mellitus and obesity are independently associated especially with sternal or mediastinal surgical site infections.

           In addition, risk factors for serious sternal surgical site infections or mediastinitis following cardiovascular surgeries include prolonged intensive care unit stay, mechanical ventilation, smoking, preexisting chronic pulmonary disease, prolonged cardiopulmonary bypass, and re-exploration. Selection of arteries used for bypass also contributes to the rate of SSI following coronary bypass surgery. The patient’s own flora  contiguous to the site of operation accounts for the majority of SSIs.

Pre-existing remote site infections

Surface micro flora can migrate from distant sites and get access into the operation site.  Untreated UTI, skin and respiratory tract infections are the three most common remote infections that have been associated with an increase in the rate of SSI. Otitis media, nasal or oral carriage of organisms, systemic infections etc. also can cause SSI. Surgery involving a site with pre existing infection, or where necrosed tissue is present, is significantly more likely to result in SSI.

Exogenous factors

·         Pre-operative hospital stay: Prolonged pre operative stay may promote proliferation of the endogenous microorganisms which can contaminate the wound heavily during the procedure. The longer the patient stays in the hospital before an operative procedure, the greater the chances for colonization of multi drug resistant hospital pathogens, eventually causing SSI.

·         Pre operative shaving: Disruptions in the skin barrier caused by the razor, promotes colonization or actual invasion with resident or exogenous microorganisms at the incision site. Shaving can cause small nicks and breaks, leaving the skin bruised and traumatized which increases the risk of colonization. Clipping of hair prior to surgery using electric clippers rather than shaving reduces the rate of SSI.

·         Improper glucose control: Control blood glucose level during surgery and postoperatively.

·         Personnel: Cleanliness and carrier stage of surgical team is an important factor in preventing SSI. Hands of surgical team harbor microorganisms that can contaminate the surgical site by direct inoculation during the operative procedure. Contamination of the site can happen through recognized and unrecognized breaks in surgical gloves. The hair and scalp, nares and oropharynges of the operating room personnel also has been shown to harbor potentially pathogenic organisms that  can be shed in large droplets and contaminate the operating field during the procedure.

·         Breaks in aseptic technique: Intact skin and mucous membranes are the body’s first line of defence against infection. But a portal of microorganism is created if the integrity of the skin is interrupted. Hence, contaminated instruments, antiseptic solutions and dressings, and technical errors can contribute to SSI. The important principle behind aseptic technique is that the susceptible site should not come in contact with any item that is not sterile and that any contaminated item should not come in contact with other area. It prevents micro organisms on hands, surfaces or equipment being transferred to operating site.

·         Antibiotic prophylaxis: Inappropriate selection of antimicrobial prophylaxis, improper timing of pre-incision dose, inadequate dose based on body mass index etc are problems related to antibiotic therapy. The goal of prophylactic antibiotic is to eradicate or retard the growth of contaminant microorganisms such that SSIs can be avoided.

·         Technical skill: The skill of the surgeon also has a central role in minimizing surgical site infection. Degree of trauma to the tissues is a determining factor to its resistance to infection and healing of the wound. The risk is also minimized by maintaining good   blood supply, gentle traction and handling of tissues, removal of necrotic tissue and eradication of dead space. Finally, skilled surgeon can reduce the duration of surgery. Surgeons with more experience acquire better technique.

·         Duration of operation: There is a direct link between the length of operation and the infection rate with clean wound rate, doubling every hour. This is because the bacterial contamination increases over time and the operative tissues are damaged by drying and other surgical manipulations. Increase in the amount of suture and electrocoagulation in prolonged surgeries may reduce the local resistance of the wound and increase suppression of host defences from blood loss and shock. The longer a wound is open, and the longer it is drained, the greater the risk of contamination.

·         Increased blood loss and number of transfusions can add to SSI. This is thought to be due to an adverse effect on cell-mediated immunity. The risk increases for each unit administered but is significantly lower when autologous blood is used.

·         Excessive OR traffic: People remain the most important source of microorganism in the environment. Excessive presence and movement of staff contributes to an increase in air-borne bacterial particles.  Microorganisms become air borne, also as a result of conversation, as it causes aerosolization of bacteria from the oropharynx. Shedding from hair or exposed skin also  increases the number of bacteria in the field.

·         Operating room ventilation: An effective ventilation system is essential to prevent patients and personnel from breathing potentially contaminated air, which can predispose them to infection. Dust accumulated on surfaces also may be disturbed and become airborne. Properly designed, installed and maintained air-conditioning system effectively reduces the number of airborne organisms by removing dust and aerosol particles.

·         Humidity and temperature also play an important role in containing SSI. Air and dust are vehicles of particles laden with microorganisms. Particulates bearing microorganisms become airborne and settle in the open wound. The potential for contamination increases each time the door to the OR opens and closes.

·         Linen: Friction of woven fibers against each other liberates lint. Disintegrated paper from disposable nonwoven products is another source of lint on fabrics. Contaminated lint on linen used for surgery, is thought to be contributing to wound infection.

Post operative Factors

·         Wound drains: Wound drains provide access to entry of organisms by hands and by colonization.

·         Wound dressing: Ineffective wound dressing protocol can contribute to SSI. A properly applied dressing can decrease pain, enhance healing, and improve cosmetic results.  Primary healing of the wound take place when tissue is cleanly cut and the margins are reapproximated well. Clean undrained wounds seal within 48 hours and are unlikely to be infected. New capillary circulation bridges the wound in 3-4 days, and once normal tissue oxygenation is achieved, the wound is considered to be healed.

Diagnosis of Surgical Site infection

Clinically a surgical site may be considered infected when purulent discharge is present at the incision site. The local manifestations of SSI include pain, tenderness at operated site, erythema, indurations, poor healing, dehiscence and presence of purulent discharge or abscess formation. However, local signs and symptoms always may not be present, nor are they necessarily due to infection when they are present. Systemic manifestations commonly include fever and other signs of sepsis. Either of the following is essential for the diagnosis of SSI. However, a positive culture is not necessary for diagnosis of a SSI.

1.   Purulent discharge from the surgical site.

2.   Positive culture report.

3.   Identification of infection by reopening and debridement of the wound.

Prevention

Because the critical event that initiates the process leading to SSI mainly occurs pre or peri-operatively, surgical site infections can be prevented by a) improving the host's defences b) reducing the amount and type of microbial contamination during surgery and c) improving wound condition at the end of the procedure through better surgical technique.

i) Preoperative measures

Adequately control blood sugar level in all diabetic patients before elective operation and maintain it at <200mg/dl during the operation and in the immediate post operative period. Instruct patients to abstain from tobacco for at least 30 days before surgery. Obesity, malnutrition, systemic diseases and other immunocompromised conditions if any, should be treated and brought under control before surgery. Identify and treat infections at other body sites. UTI, respiratory tract and skin infections, otitis media, nasal or oral carriage of organisms, systemic infections etc. if any, should be corrected before an elective operative procedure. Pre operative hospitalization to be kept to a minimum. The ideal for elective operations would be to admit the patients to the hospital on previous day or on the day of surgery. Set criteria for hair removal based on the need to view or access the operative site rather than to reduce bacteria.  If shaving is thought to be necessary for any reason, it should be performed immediately before the procedure, to reduce the risk of infection. Pre operative bathing with an antimicrobial product (povidone iodine 7.5%) is recommended at the night before and morning of the operation.Thoroughly wash and clean at and around the incision site to remove gross contamination before shifting the patient to theatre. Sterile occlusive drapes may then be used to prevent recontamination of the area. Administer antibiotic relevant for the proposed procedure an hour prior to making incision. Repeat it at 3 hrs in procedures of >3 hours duration.

ii)  Intra-operative measures

Laminar flow ventilation system, a controlled, unidirectional, positive pressure stream of air and high-efficiency particulate air (HEPA) filters further reduces the airborne contamination to very low levels. The door to the operating room should be closed at all times to avoid mixing corridor air with the operating room air, which would increase the microbial load. To prevent contaminated air from reaching the operating theatre, a properly designed, air-conditioning system is recommended. The minimum air exchanges required for operation room is 15 air changes per hour of which 3 should be of fresh air. The air within the operating room should be at a positive pressure compared with other areas of operating suit with movement from clean to less clean areas. Introduce all air vent at the ceiling and exhaust near the floor. Air filters need to be replaced regularly according to manufacturer's instructions. The temperature required for operating room is 20-23 0C. The designated relative humidity is 30 to 60%. Levels greater than 60% promote fungal growth.

Restrict the number of people allowed in the operating room, and the activity of the personnel, including talking, to an absolute minimum. Carriers of bacteria and people with septic lesions should refrain from entering theatre. Infected cases should preferably be placed last in the list. Waste removal, concurrent cleaning and disinfection of operating room should be done between each cases. All clinical waste should be disposed of according to the guidelines. Wet-mop the floor of the operating room with a disinfectant between cases to minimize the risk of the operating room environment and floors as a source of infection. When large soiling or contamination, with blood or other body fluids, of surface or equipment occurs during an operation, use 1% sodium hypochlorite solution to clean the affected area before the next operation.

Terminal cleaning and disinfection of theatre is to be performed daily after the cases are over. A more thorough wet cleaning / vacuuming of the entire suit at the end of the day provide a sufficiently clean environment. Weekly washing of theatre suit and all its equipment using a detergent disinfectant followed by disinfection of operating rooms is recommended to keep the theatre free of contamination. Fogging is recommended after a patient having airborne pathogens is encountered. Whenever contamination with air borne pathogen is suspected, institute policy recommends fogging, using hydrogen peroxide in silver nitrate base (ecoshield). Required strength is 20%.  However, cleaning, pre and post to fogging, plays the important role.

To avoid transfer of pathogens in to the operating site, operating room apparel must be worn only within the surgical suite. If it happens to be taken outside, it should be removed before the person reenters the suite. The surgical hand scrub is intended to reduce the number of both transient and resident microorganisms on hands of personnel who comes directly in contact with the wound. Remove hand jewels and wrist watch before performing hand scrub. Finger nails should be kept short and clean underneath each fingernail before performing hand scrub. Scrub is to be performed before the sterile field, sterile instruments or the patient's prepared skin is touched. Scrub should include hands and forearms up to the elbows. Thorough surgical scrub for 3-5 minutes helps to prevent transfer of microorganisms from personnel to patient. Team members having any weeping lesions or dermatitis on hand should refrain from duty.

Barrier devices are meant to prevent wound contamination from shedding of skin squames embedded with organisms by operating room personnel. All those who enter operating theatre ought to wear mask. Double layered face mask prevent aerosolization of droplets generated during conversation. A fresh mask must be worn for each operation as the wet mask is potential for transferring organism. Hair must be completely covered by a close fitting cap and beard cover (if indicated). Plastic over shoes that is washable and covers the whole foot is recommended in the operating suite. Protective eye wear or face shields safeguard the team members from exposure to splashes / droplets of blood / body fluids likely to be generated during the procedure. The operating team should wear sterile gown having long sleeves at surgery. Change scrub suit when visibly soiled, contaminated, and / or penetrated by blood or other potentially infectious materials.

iii)  Aseptic surgical technique

Good operative technique includes: expeditious surgery, use of aseptic barriers, gentle handling of tissue, reduction of blood loss and hematoma formation, elimination of dead tissue, debridement of devitalized tissue, removal of all purulent material by irrigation or suction and removal of all foreign material from the wound before closing. Use delayed primary closure or leave incision open to close by secondary intention, if the site is heavily contaminated. If drain is indicated, use a closed suction drain and place the drain through a separate incision. Remove the drain as soon as possible.

Ensure proper packaging, sterilizing, and maintaining of instruments sterility till the end of the procedure. All sterile packs should be opened using non touch technique. Either autoclaving or plasma sterilization is recommended for instruments. Do not perform flash sterilization.

iv) Post operative care

Protect primary closure incisions with sterile dressing for 24-48 hours post operatively and should not be opened in 48 hrs unless infection is suspected. Observe hand hygiene, aseptic technique and use sterile gloves and dressing material for wound dressing. Use woven gauze dressings, as it does not interact with wound and thus causes less wound irritation. Dry dressings are preferred for post operative incisions that are expected to be primary intention healing. Use separate swab for each cleansing stroke. Clean from least contaminated area to most contaminated. Frequency of dressing should be kept to a minimum.

Dispose the soiled dressings and drains according to the guidelines. Care of wound should be directed at encouraging rapid wound healing by providing adequate nutrition. A diet rich in protein, vitamins and minerals need to be advised. Avoid excess post operative stay and overcrowding of people in the post operative unit. Keep post operative unit clean and keep the patient away from infected or colonized patient. Surveillance of surgical site infection with regular feedback of appropriate data to the surgeon has been shown to be an important strategy to reduce the risk of SSI.

CONCLUSION

Every individual is accountable for his/her own role in infection control. The nurse has a major role in preventing the transmission of bacteria in wounds between patients and in minimizing the risk of developing SSI. As knowledge, technology, and health-care settings change, infection control and prevention measures also should change. 

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