CHAPTER 6 Infection and surgery
The surgical patient is exposed to potentially harmful microorganisms prior to admission, during admission and after discharge. The outside surfaces of the body, including the aerodigestive tract, are normally colonized with bacteria – a defence mechanism that is disrupted by stress and antibiotic therapy. With the prevalence of hospital acquired infections, such as clostridium difficile and methicillin-resistant staphylococcus aureus (MRSA), and the potential for blood-borne virus transmission, the practicing surgeon needs to be aware of safe antimicrobial techniques and treatments, to protect both the patient and healthcare staff. Effective communication needs therefore to be present between surgeon and microbiologist.
When appropriate, the wound edges are approximated as soon after the injury as possible, e.g. clean traumatic wounds or surgical incisions. This is known as primary closure and the wound heals by first intention.
The wound edges are not apposed and the wound is left to heal by second intention. Granulation tissue grows up from the base of the wound and the skin grows over in a centripetal manner. This type of healing is appropriate for large, grossly contaminated wounds.
The wound is left open and observed for several days. If the wound then appears healthy, it may be closed as for a primary closure. This type of closure is suitable for wounds that have low-grade infection or for surgical incisions where infection may be expected, e.g. abdominal incisions following operations for gross faecal peritonitis.
An incision in which no inflammation is encountered in a surgical procedure, without a break in sterile technique, and during which the respiratory tract, alimentary or genitourinary tracts are not entered, e.g. varicose vein surgery, hernia repair. The risk of postoperative wound infection is about 5%.
An incision through which the respiratory, alimentary, or genitourinary tract is entered under controlled conditions but with no contamination encountered, e.g. cholecystectomy, partial gastrectomy. The risk of postoperative wound infection is about 10%.
An incision undertaken during an operation, in which there is a major break in sterile technique or gross spillage from the gastrointestinal tract, or an incision in which acute, non-purulent inflammation is encountered. Open traumatic wounds >12–24 h old. The risk of postoperative wound infection is >50%.
Antibiotics are never a substitute for sound surgical technique. Pus, dead tissue and slough need removing. Antibiotics should be used carefully and only with positive indications. Prolonged or inappropriate use of antibiotics may encourage resistant strains of organisms to emerge. Except in straightforward cases, advice of a microbiologist should be sought.
The decision to prescribe antibiotics is usually clinical and is based initially on a ‘best-guess’ policy, i.e. based on experience of that particular condition, what the organism is likely to be, and to what it is most likely to be sensitive. The following sequence of events usually occurs:
Antibiotics should be given i.v. in severe infections in seriously ill patients. Some antibiotics, e.g. gentamicin, can only be given by the parenteral route. When the patient improves and the GI tract is functioning satisfactorily, drugs may be given orally.
This depends on the individual’s response, laboratory tests and the underlying cause of infection. For most infections that show an appropriate response to treatment after 48 h, a suitable ‘course’ should be for 5–7 days. Infections such as osteomyelitis require prolonged courses of antibiotics administered long after symptoms and signs of infection have resolved.
Despite aseptic techniques, some operations carry a high risk of postoperative wound infection, bacteraemia or septicaemia. Administration of antibiotics in the perioperative period will reduce the risks.