Surgical site infection is a common complication of surgery. With the increasing trend to day-case or short-stay surgical it is unusual to see it in hospital practice as patients are discharged to primary care before it becomes manifest. Careful defi nition, assessed by a blinded trained observer with an adequate follow-up period (e.g. 6 weeks) is the only way to be sure of infection rates. The median time to a wound infec- tion is 8–10 days; spreading cellulitis caused by B-haemolytic Streptococci may be seen 3–4 days after surgery, whereas some superfi cial and deep
Staphylococcal infections may manifest themselves 5–6 weeks post-
operatively. In the case of orthopaedic, prosthetic hip and knee surgery, SSIs can present up to and even beyond a year after surgery.
Recognition and treatment of superfi cial surgical site infections is often transferred to primary healthcare, where recognition may be delayed and inappropriate treatment given (antibiotics instead of removal of a suture to release pus, for example). SSIs can be expensive to healthcare services, particularly when complex procedures have to be used for their management or when there is a delay in return home. Post-discharge surveillance of SSI rates is clearly important and the following defi nitions and classifi cation should be used for this purpose.
Defi nition of surgical site infection
For audit purposes it is critical that wounds are assessed by a trained unbiased observer using adequate defi nitions. A wound infection may be described as the discharge of pus or fl uid from which a pathogen can be cultured, sometimes with spreading erythema. A 30-day surveillance should be used for best accuracy, a period advocated by the American Centers for Disease Control. Most SSIs are superfi cial, involving the skin or subcutaneous layers. Deep incisional SSIs involve the musculofascial layers, and organ or cavity SSIs might present as a liver abscess after hepa- tobiliary surgery or an empyema after a lung operation.
A minor wound infection should not delay the planned date of return home, but a major one may do so with systemic complications of pyrexia and SIRS (see later) and with wound disruption. The grading of wound infection is usually reserved for research purposes, a useful scheme being the ASEPSIS score based on Additional treatment, the presence of Serous discharge, Erythema, Purulent exudate, Separation of deep tissues, Isolation of bacteria, and the duration of inpatient Stay. In research the interval data given by a scoring system are more useful than categorical present or absent data.
The cause of infection can be related to the time of bacterial exposure. Exogenous SSIs arise from an external source (e.g. poor theatre environment with inadequate laminar fl ow or air fi ltration, or poor ward discipline of contaminated hands at dressing change). Endogenous SSIs arise from patients’ own bacterial fl ora (e.g. organisms from their own skin or bowel) during surgery.
33
SURGICAL SITE INFECTION (SSI)
Classifi cation of SSI
This has been traditionally related to the theoretical risk of con- tamination (b see Table 2.1), and there is evidence that these classes do work. It has been estimated that contamination with 106 potential
pathogens/gram of tissue is required to lead to a wound infection, but this is exponentially lower, as few as 100–1000 organisms, in the pres- ence of ischaemia or foreign bodies (such as silk sutures or prosthetic grafts). Antibiotic prophylaxis is given empirically to cover the spectrum of anticipated organisms (e.g. fl ucloxacillin in clean prosthetic surgery against Staphylococci; or cefuroxime and metronidazole in elective colonic surgery to cover aerobes such as Escherichia coli and anaerobes such as
Bacteroides spp.).
Rational antibiotic prophylaxis has been associated with falls in wound infection from 20–30% to <10% in clean contaminated operations; 60% to 15–20% in contaminated surgery, and over 60% to <40% in dirty surgery. There is currently some controversy surrounding wound infection rates after non-prosthetic, clean-wound surgery, particularly for breast surgery, where rates of >15% have been reported when in-depth post-discharge surveillance has been used. The use of prophylactic antibiotics is also controversial but the evidence of their value in clean, prosthetic surgery is not contested. In vascular graft surgery and orthopaedic joint surgery, infection rates should be less than 5% and 1%, respectively; antibiotic prophylaxis is extended for 24 hours in such surgery. However, there is no substitute for aseptic technique (together with ultraclean air in orthopaedics), as infection in these fi elds of surgery can be disastrous with high rates of mortality and morbidity and revision surgery.
In dirty surgery, the rate of wound infection is so high with its attendant risks of superfi cial and deep wound disruption that a case for leaving the wound open can be made. Infection is thereby minimized and once there is a clean granulating wound it can be closed by delayed primary (within fi ve days) or secondary closure. Antibiotic prophylaxis in such cases should be extended as treatment for fi ve days. There are many other risk factors than operative site contamination (b see Table 2.2).
34
CHAPTER 2Infection
Table 2.1 Categories of wound contamination
Ia clean
(e.g. hernia, varicose veins, breast)
hollow viscus not opened no infl ammatory process encountered
Ib clean prosthetic surgery (e.g. vascular grafts, joint prosthesis)
no break in aseptic ritual II clean-contaminated (e.g. elective open
cholecystectomy)
GIT, RT, or UGT opened without signifi cant spillage III contaminated (e.g. appendicectomy or
elective colorectal surgery)
acute infl ammation encountered without pus
gross spillage from an open viscus or major break in asepsis IV dirty (e.g. abscess or faecal peritonitis) pus or perforated viscus
encountered GIT – gastrointestinal tract; RT – respiratory tract; UGT – urogenital tract.
Table 2.2 Risk factors for wound infection (few have a level one evidence base)
Local operative technique (haematoma or roughly handled tissues)
thin devascularized skin fl aps (local hypoxia) infl ammatory disease (without infection being present) previous surgery (breast biopsy)
Systemic malnutrition
blood transfusion age
immunosuppression of any cause chemotherapy or radiotherapy
medical complications (diabetes, renal or liver failure, vascular disease)
shock of any cause (haemorrhagic, septic, myocardial infarction) cancer
remote infections
General factors long pre-operative hospital stay long operations
shaving (which ought to be immediately pre-operatively, if undertaken at all)
use of pre-operative antiseptic showers operating theatre and ward rituals
35
SURGICAL SITE INFECTION (SSI)
Management of wound abscess/infection
Release pus, remove any retaining sutures, and ensure adequate •
drainage.
Debride necrotic non-viable tissue; this may need several sessions, •
including general anaesthetic in the operating theatre.
Antibiotic empirical therapy (or based on microbiological analyses) •
for associated cellulitis, lymphangitis, or systemic complications of sepsis or bacteraemia.
Topical antimicrobials (such as povidone iodine – which is useful against •
meticillin resistant Staphylococcus aureus (MRSA) – or chlorhexidine). Keep wound moist with appropriate surgical dressings.
•
In the presence of clean granulations consider grafting or secondary •
suture.
When taking pus from an infected wound, fresh specimens (large volumes of pus preferably in a sterile pot rather than on a swab) need to be sent for microbiological identifi cation and sensitivities. Communication with a microbiologist gives the best results and the best choice of an antibiotic if needed.