Surgical Site Infections

Infections following neurosurgical procedures are uncommon and result from bacterial seeding at the time of the operation. The risk for infection is at least partially dependent on the potential for perioperative contamination of the wound (Table 4). Additional risk factors in adult patients include a CSF leak, subsequent operation following the primary procedure, emergency surgery, concurrent infection at a distant site, and an operative time of longer than 4 hours.

An infected surgical wound is erythematous, painful, swollen and does not heal. Sutures should be removed and any purulent drainage should be cultured. S. aureus is isolated from 50% to 60% of wound infections. Less commonly, coagulase negative staphylococci, Streptococci species and members of the family Enterobacteri-aceae cause wound infections. No organism is identified in one-quarter of patients.

Bone flap infection occurs in up to 5% of craniotomies with free bone flap placement, making this one of the most common neurosurgical procedures complicated by infection. Because devitalized tissue impedes antimicrobial penetration

Table 4. Incidence of surgical site infection in neurosurgery patients according to surgical category'

Surgical Category

Definition

Example

Incidence of Surgical Site Infection (%)

Clean

No known risk Elective surgery, ideal 2.6

for infection conditions

Foreign body left VPS insertion 6.0 in situ

Risk of contamination Surgical entry via 6.8

during surgery paranasal air

Clean with foreign body

Clean contaminated

sinuses

Contaminated

Contamination known Scalp laceration at the 9.7

to have occurred surgical site

Established infection Drainage of brain 9.1

at the time of the abscess operation

Dirty

* Modified from Narotam PK et al. Operative sepsis in neurosurgery: A method of classifying surgical cases. Neurosurgery 1994; 34:409-416.

and resolution of infection, debridement of infected bone is recommended. S. aureus and coagulase-negative staphylococci are the most frequent pathogens cultured from infected bone flaps.

Meningitis-ventriculitis, brain abscess and subdural empyema are rare following neurosurgery. Postoperative meningitis is difficult to diagnose because some patients develop an aseptic or chemical meningitis following craniotomy that mimics bacterial meningitis. In addition, CSF findings in aseptic and bacterial meningitis overlap, and 70% of patients with culture proven meningitis have a negative initial CSF Gram-stain.

The choice of empiric antibiotics depends on the site of infection and the primary procedure. If the sinuses were entered during the operation, anaerobic coverage is indicated. Gram-negative coverage is included when the surgery transversed the abdomen. Nafcillin is appropriate for wound infections, but vancomycin is recommended as initial empiric therapy for bone flap infections because a high proportion of coagulase-negative staphylococci are resistant to methicillin.

Consensus is lacking regarding indications for use of prophylactic antibiotics in neurosurgery. Most studies of all surgical procedures demonstrate a benefit from using a single dose of preoperative antibiotics. No evidence exists to support the use of routine postoperative antibiotics.

Currently prophylactic antibiotics are used for dirty procedures, procedures that transverse the nasopharyngeal mucosa, procedures using prosthetic material (VPS insertion) and craniotomy. Because patients with established infection at the time of the procedure are receiving pathogen-directed therapy, prophylaxis is not necessary.

The choice of antibiotics is influenced by the susceptibility pattern of the most common pathogen causing infection. A first generation cephalosporin is often used because of good activity against methicillin-susceptible staphylococci. Vancomycin is used in penicillin-allergic patients, and in hospitals where a large proportion of infections are caused by methicillin-resistant staphylococci. A single dose of antibiotic given immediately prior to the start of the surgery provides adequate tissue levels that are sustained throughout the duration of the operation. A dose of cephalosporin should be repeated for procedures that extend beyond 4 hours to maintain systemic levels. Because of a longer serum half-life, an additional intraoperative dose of vancomycin is not necessary until 6 hours. There are no data demonstrating that continuation of prophylaxis into the postoperative period reduces the rate of surgical site infection. Thus, 1 or 2 doses of antibiotics are sufficient for most procedures, and dosing beyond the perioperative period is not recommended.

Suggested Readings

1. Behrman RE, Kliegman RM, Jenson HB, eds. Nelson Textbook of Pediatrics. 17th ed. Philadelphia: Saunders, 2004:Part XVI—Infectious Diseases.

2. Long SS, Pickering LK, Prober CG, eds. Principles and practice of pediatric infectious diseases. 2nd ed. New York: Churchill Livingstone, 2003.

3. Yogev R, Bar-Meir M. Management of brain abscesses in children. Pediatr Infect Dis J 2004; 23:157-159.

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