Infection and surgery

CHAPTER 6 Infection and surgery

Principles of wound management 98
Prevention of surgical site infection 99
Antibiotics in surgery 100
Surgical infections 102
Methicillin-resistant Staphylococcus aureus (MRSA) 110
Infection and the surgeon 110

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.

Principles of wound management

Healing by primary intention

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.

Healing by secondary 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.

Delayed primary closure

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.

Factors affecting wound healing

Age

Younger patients heal better than older patients.

Nutritional state

Malnutrition impedes wound healing. Patients who are poorly nourished should be given appropriate feeding, e.g. TPN prior to surgery.

Drugs

Steroids delay wound healing.

Tissue oxygenation and vascularity

Hypoxaemia and ischaemia delay wound healing. Highly vascular areas, e.g. face, heal quicker than poorly vascularized areas, e.g. shin.

Radiotherapy

Causes endarteritis obliterans of small vessels resulting in local ischaemia and poor healing.

Local sepsis

This is probably the commonest cause of delayed healing.

Factors predisposing to infection in surgery

Age

Increasing age is a significant independent predictor of risk.

Underlying illness

Those with an American Society of Anesthesiologists (ASA) score of 3 or more have been found to have a significantly higher risk of surgical site infection.

Obesity and smoking

Are both associated with an increased risk of surgical site infection.

Wound classification

See below.

Classification of surgical wounds

Clean

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%.

Clean contaminated

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%.

Contaminated

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%.

Dirty

An incision undertaken during an operation in which the viscera are perforated or when acute inflammation with pus is encountered (e.g. faecal peritonitis), and for traumatic wounds where treatment is delayed, there is faecal contamination, or devitalized tissue is present.

PREVENTION OF SURGICAL SITE INFECTION (Incorporating NICE guidelines 2008)

Preoperative precautions

• Adjust patient lifestyle. Improve diet and body mass index. Advise to stop smoking
• MRSA screening and subsequent decolonization if positive (see below)
• Consideration of delay of elective surgery if concurrent infection detected
• Advise patients to take a bath or shower using soap within 24 h prior to surgery
• If hair removal desired, use electric clippers on the day of surgery.

Perioperative precautions

• Staff to wear specific non-sterile theatre wear in operating suite, sterile gowns in the theatre
• Keep staff movements in and out of theatre to a minimum
• Operating team to remove hand jewellery, nail polish and artificial nails
• Scrub hands with nail cleaning with a brush or pick prior to the first operation
• Scrub hands prior to subsequent operations and if hands soiled
• Patient skin preparation with povidone-iodine or chlorhexidine prior to incision
• Maintain adequate patient temperature, oxygenation and perfusion throughout
• Cover surgical wounds with an appropriate dressing at the end.

Postoperative precautions

• Use an aseptic technique to change dressings
• Use sterile saline to cleanse wound up to 48 h after surgery
• Patients may shower 48 h after surgery
• Use an appropriate dressing for wounds healing by secondary intention.

Antibiotics in surgery

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.

Principles of antibiotic therapy

Selection of antibiotic

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:

1. A decision is made on clinical grounds that an infection exists.
2. Based on signs, symptoms and clinical experience, a guess is made at the likely infecting organism.
3. The appropriate specimens are taken for microbiological examination, i.e. culture and sensitivity testing.
4. The most effective drug against the suspected organism is given in line with individual hospital guidelines. If doubt exists this is discussed with a microbiologist.
5. The clinical response to treatment is monitored.
6. The antibiotic treatment is altered, if necessary, in response to laboratory reports of culture and sensitivities.

Occasionally the response of the infection to an apparently appropriate antibiotic is poor. Possible causes for this include:

• Failure to drain pus, excise necrotic tissue or remove foreign bodies
• Failure of the drug to reach the tissues in therapeutic concentrations, e.g. ischaemic limbs
• Organism isolated is not the one responsible for the infection
• After prolonged antibiotic therapy, new organisms develop due to selection pressure
• Inadequate dosage or inappropriate route of administration.

Route of administration

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.

imageIt is best to avoid the intramuscular route if possible as it is uncomfortable for the patient and in shocked patients absorption would be inadequate.

Duration of therapy

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.

Dosage

The dosage may need to be modified in renal and liver disease.

Complications of antibiotic therapy

• Adverse reactions
— Side-effects, e.g. nephrotoxicity, ototoxicity
— Hypersensitivity
— Anaphylaxis
• Development of resistance
• Iatrogenic infection, e.g. Clostridium difficile with the use of cephalosporins, clindamycin.

Prophylactic antibiotics

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.

Indications for prophylactic antibiotics

These include:

• Implantation of foreign bodies, e.g. cardiac prosthetic valves, artificial joints, prosthetic vascular grafts
• Patients with pre-existing cardiac disease who are undergoing surgical procedures including dental procedures, e.g. patients with mitral valve disease as prophylaxis against infective endocarditis
• Organ transplantation
• Immunosuppressed patients
• Diabetics
• Amputations, especially for ischaemia or crush injuries, where there is dead muscle; risk of gas gangrene is high especially in contaminated wounds; penicillin is the antibiotic of choice

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Jun 14, 2017 | Posted by in GENERAL SURGERY | Comments Off on Infection and surgery

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