Antibiotic prophylaxis in neurosurgery and skull fracture

Introduction

A Working Party of the British Society for Antimicrobial Chemotherapy reviewed the literature in this important area to identify areas of clinical benefit and to make recommendations on appropriate use of antimicrobials.

The important factors influencing the choice of antibiotic prophylaxis in neurosurgery are:

Patient immune status
Virulence of the pathogens
Type and duration of surgery.

It is also important to ensure adequate penetration of the antibiotic into the brain: however, the blood–brain barrier is disrupted in surgery, allowing agents with otherwise poor penetration to access the brain.

Clean, non-implant (procedure does not cross the cranial sinuses)
Clean-contaminated (procedure crosses the cranial sinuses)
CSF shunt surgery
Skull fracture.

Clean non-implant surgery

There is a great deal of evidence showing that antibiotic prophylaxis is statistically significantly better than either placebo or no treatment for clean non-implant surgery.

There are few comparative studies. The BSAC Working Party endorsed the use of antibiotic prophylaxis based on the following criteria:

Therapeutic concentration in the operative field (ability to penetrate into the CSF is not important)
Nature and susceptibility of the likely pathogens.

Likely pathogens

Staphylococcus aureus (approximately 50%)
Coagulase-negative Staphylococcus spp. (approximately 15%)
Aerobic Gram-negative bacilli (approximately 15%)
Streptococcus spp. (approximately 10%)
Others (<10%).

The chosen antibiotic needs to be effective against Staphylococcus aureus as well as other Gram-positive cocci and Gram-negative bacilli. A first- or second-generation cephalosporin has the required spectrum of activity.

The recommended prophylaxis in clean non-implant surgery in adults is:

Cephradine 1 g IV at induction of anaesthesia and every 3 h during surgery
or
Cefuroxime 1.5 g IV at induction of anaesthesia and every 3 h during surgery.

There is no evidence that extending the duration of prophylaxis is beneficial.

The use of the following antibiotics has been reported but they are sub-optimal choices for the following reasons:

Antibiotic	Reason for sub-optimal choice
Benzylpenicillin	Possibility of resistant strains of Staphylococcus aureus
Metronidazole	Anaerobe involvement very rare
Vancomycin with or without gentamicin or tobramycin	Few multi-resistant strains to justify general prophylaxis with these compound
Flucloxacillin	No effect against Gram-negative bacilli
Third-generation cephalosporins and other novel beta-lactams eg. cefotaxime, cefuroxime, imipenem	Multi-resistant Gram-negative organisms uncommon

Clean-contaminated procedures

Any procedure that crosses the naso- or oropharynx can introduce a wide range of local flora. The BSAC Working Party concluded that antibiotic prophylaxis was appropriate: prophylaxis with a broad-spectrum beta-lactamase-stable penicillin is suitable for most patients.

Co-amoxiclav 1.2 g IV at induction of anaesthesia and every 3 h during surgery
Cephradine 1 g IV plus metronidazole 500 mg IV at induction of anaesthesia and every 3 h during surgery
or
Cefuroxime 1.5 g IV plus metronidazole 500 mg IV at induction of anaesthesia and every 3 h during surgery.

In penicillin-allergic patients:

Gentamicinplus metronidazole.

CSF shunt surgery

Antibiotic prophylaxis has no clear benefit in CSF shunt surgery. Most individual studies show no benefit, but pooled studies have shown a benefit, though this is probably a statistical artefact. There is no consensus on the method of administration of antibiotics.

Given the disparity in the data it is impossible to either endorse or reject the use of antibiotic prophylaxis for CSF shunt surgery. The decision to use prophylaxis must be a surgical one and if prophylaxis is chosen the following guidance may be useful.

Infections are predominantly caused by:

Coagulase-negative Staphylococcus spp.(up to 90%)
Staphylococcus aureus (13–27%)
Aerobic Gram-negative bacilli (10–20%)
Wide range of other organisms.

Vancomycin plus gentamicin provides the most effective cover against this spectrum of pathogens but neither antibiotic penetrates the CSF well enough in patients with non-inflamed meninges if given IV; therefore if this combination is chosen the agents should be instilled directly into the ventricles. External infection is rare but a single IV dose of a first- or second-generation cephalosporin, eg. cephradine 1 g or cefuroxime 1.5 g respectively, should provide protection.

Shunts impregnated with rifampicin plus clindamycin help to prevent colonisation.

Skull fracture

Meningitis can be a serious complication following a skull fracture. In general, approximately 11–25% of patients with CSF leaks become infected.

In patients with skull fractures, post-traumatic meningitis is predominately caused by the pneumococcus. However, patients that have had lengthy hospital stays, who have recently received antibiotics or who have penetrating or open wounds may become infected with Staphylococcus aureus and aerobic Gram-negative bacilli.

Skull fracture with a CSF leak accounts for a small percentage of head injuries requiring hospital admission and this has made it difficult to undertake studies to investigate the role of prophylaxis. This means there is still uncertainty over the role of prophylaxis in skull fracture, but the Infection in Neurosurgery Working Party of the BSAC concluded that the available evidence does not support the use of prophylactic antibiotics in patients with a skull fracture and CSF fistulae.