Introduction

Surgical wound infections are common, comprising 12% of all hospital-acquired infections.  The rate of infection varies depending on the type of surgery undertaken.  Especially high rates are associated with contaminated surgery, such as colorectal surgery or delayed surgery to traumatic wounds.

Aetiology of surgical wound infections

Wound infections are usually caused by the patient’s normal flora, or by bacteria from the environment or the skin of hospital staff.  The commonest organism is Staphylococcus aureus.  Other common causative organisms include other Gram-negative aerobes, Streptococcus spp. and anaerobes.

Diagnosis of surgical wound infections

Redness, swelling and pain are the signs of infection in a wound


Click to enlarge

 

Clinical

Isolation of bacteria from the wound is not diagnostic for surgical wound infection without clinical signs of infection (redness, swelling and pain). 

 

 

Microbiology

Management of surgical wound infections

The type of surgery (clean, clean/contaminated, contaminated or dirty) will determine the risk level of infection and the likely spectrum of pathogens.  Empirical therapy should be primarily directed against Staphylococcus aureus.

If wounds are not grossly infected, they may respond to local measures such as removal of sutures.  Frequent saline bathing should be undertaken and the wound requires a drain to allow healing.  Deep-seated infection related to complicated abdominal surgery may require broad-spectrum antibiotics and investigation for possible surgical intervention.

Empirical therapy

Empirical treatment may include:

Type of surgery

Probable pathogens

Empirical therapy

Clean

Clean/contaminated

Staphylococcus aureus

High dose flucloxacillin

In penicillin-allergicpatients, clindamycin

Contaminated

Dirty

Aerobes and anaerobes

 A second-generation cephalosporin such as cefuroxime plus metronidazole
or
co-amoxiclav

In many surgical operations, patients will have previously received antibiotic prophylaxis.  This varies according to the type of operation.  Prophylaxis will affect the flora and thus the cause of any subsequent infection.  It is therefore important to determine the nature of any prior antibiotic therapy, as this will determine the agents likely to be successful in any subsequent infection.

Prevention of surgical wound infection

Antibiotic prophylaxis has been shown to decrease the risk of infection in certain types of surgery.

Antibiotic Prophylaxis in Surgery Scottish Intercollegiate Guidelines Network.

The goals of antibiotic prophylaxis are to achieve inhibitory antibiotic levels at incision and throughout the procedure. Animal studies have shown that antibiotic prophylaxis is most effective in preventing post-surgical infections when administered before the start of surgery and pharmacokinetic data suggest administration as near the time of incision as possible.

If intramuscular antibiotics are used they should be given one hour before the start of surgery.  Intravenous antibiotics should be given during the induction of anaesthesia with repeat doses for longer procedures. 

The benefits of post-operative prophylaxis lasting more than 12 h have not been proven.

Indications for prophylaxis

Prophylaxis is particularly recommended in surgery where there is a high-risk of infection such as abdominal surgery or where the development of infection would be very serious eg. prosthetic joint replacement.

Indications for prophylaxis in clean surgery where infection would be very serious include:

  • Arterial grafts and vascular surgery
  • Cardiac surgery
  • Spinal surgery
  • Transrectal prostatic biopsy
  • Joint prostheses.

Prophylaxis is also recommended in clean surgery with a high-risk of infection:

  • Severe injuries and burns (risk of Clostridium tetani and Clostridium perfringens)
  • High amputation of ischaemic legs (risk of Clostridium perfringens).

Prophylaxis against surgical sepsis is recommended when an internal organ that has a high bacterial content is opened:

  • Operations on the stomach or oesophagus in patients with carcinoma or bile reflux gastritis
  • Cholecystectomy in patients who may have infected bile or are at risk of sepsis (not laparoscopic procedures)
  • Intestinal surgery in patients with inflammatory bowel disease
  • Colorectal surgery involving resection and/or anastomosis
  • Patients with a perforated gangrenous appendix
  • Pelvic operations.

The requirement for prophylaxis is more controversial in other types of surgery, such as:

  • Pelvic operations in patients with recurrent cystitis
  • All instrumentation in the presence of bacteriuria
  • Urethral dilatation
  • Neurosurgical operations involving foreign materials.

Refer to local guidelines and policies in these situations.

However, the expected duration of operation — the longer the operation the greater the risk of infection — and the health status of the patient both affect the decision to prescribe prophylactic antibiotics. 

If the antibiotic cannot be given as an IV bolus, the administration should be timed to achieve maximum concentrations at the time of the incision.  If there is excessive blood loss (more than 1500 mL) during an operation then an additional dose of prophylactic antibiotic should be given after fluid replacement.

If a tourniquet is to be used on a limb, then antibiotic administration should take place before tourniquet application; adequate tissue concentrations probably occur within 10 min of injection.

Typical prophylactic regimens include: