Hydrocephalus And Shunts

stages. Abdominal ultrasound examination, looking for encysted collections of CSF, may be useful in such cases (see above).

Blood cultures are frequently unhelpful in diagnosing VP shunt infection; however, measurement of C-reactive protein (CRP) can be a useful guide, both as part of the initial investigation and as a means of monitoring the effectiveness of treatment.

Organisms Responsible for Shunt Infection

The commensal skin flora is the usual source of pathogens that give rise to shunt infections with the coagulase-negative staphylococci, particularly S. epidermidis, the most commonly isolated. S. aureus is also well recognized, especially in the context of wound infection or skin breakdown. Enterococci, micrococci and coryneforms account for a significant proportion of the remainder of infecting organisms (Table 24.4).

One of the principal factors which enables coagulase-negative staphylocci to colonize shunt systems is their ability to produce an extracellular slime, which aids adherence of the organisms to the surface of the silicone catheter [20]. This is also one of the main factors responsible for the resilience of these infections to treatment with the shunt in situ.

Treatment of Shunt Infection Once diagnosed, shunt infection requires prompt and comprehensive treatment with appropriate anti-microbial therapy. Controversy exists, however, as to whether treatment necessitates complete removal of the shunt system or whether the infection can be managed

Data from Great Ormond Street Hospital 1994-97. Courtesy of Dr H. Holzel, Dept of Microbiology (unpublished).

with the shunt in situ. Those who favor treating the infection with the shunt in situ cite the risks of shunt removal, including hemorrhage, from adherent ventricular catheters and the risk of super-added infection associated with temporary external ventricular drainage in support of their policy. The success rates associated with this line of management, however, are poor [21] and the overall morbidity associated with surgical treatment (shunt removal and antibiotic therapy) is lower than with medical therapy alone.

The most common strategy is removal of the shunt and replacement with an external drain for the duration of antibiotic treatment. This permits intrathecal administration of antibiotics if required and serial sampling of the CSF for Gram stain, culture and monitoring of the white cell response. A new shunt is inserted once the CSF is sterilized.

The Role of Antibiotic Prophylaxis in Shunt Surgery

The temporal relationship between time of operation and the occurrence of shunt infection, together with the observation that the commensal skin flora is the commonest source of pathogens, might suggest that antibiotics given at the time of surgery would reduce the incidence of infectious complications. Although there have been numerous studies attempting to demonstrate this, most have failed to reach statistically significant conclusions. One of the principal problems has been enrolling sufficient patients into randomized trials to demonstrate an effect. Two reports have sought to circumvent this problem of type II error using the techniques of metanalysis [22,23]. Both of these reports came out in favor of prophylaxis. Haines and Walters, however, caution that any demonstrable benefit is related to the baseline infection rate; no beneficial effect could be demonstrated when this was less than 5%.

Additional controversy then surrounds the issue of the choice of antibiotic, its route of administration and the duration of prophylaxis. Many antibiotics, including vancomycin, cephalosporins and aminoglycosides, when administered via the intravenous route, fail to achieve significant levels in the CSF, particularly in the absence of inflammation and are thus inappropriate in this respect. Some workers have suggested intraventricular administration

Table 24.4. Organisms responsible for shunt infection.

Organism

Number

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