Shunt Infection

Infection was a common complication of CSF shunts, occurring in up to one-third of shunted patients. With improved techniques and shunts, infection rates have decreased to 5 to 8 percent per procedure.2 The highest rates of infection are found in the very young and old, and in patients who have had multiple shunt revisions. There is no association between shunt type and infection rates.

Half of all shunt infections present within the first two weeks of placement, 70 percent present within two months of placement, and 80 percent of shunt infections present within six months of placement. CSF shunt infection can be categorized into internal and external infections. An internal infection involves the shunt and the CSF contained within that shunt. External infections involve the subcutaneous tract around the shunt, which is usually tender and there is often an associated fluid collection within the skin. If diagnosed and treated in a timely fashion, mortality from shunt infections is low. However, if ventriculitis develops, mortality is 30 to 40 percent, underscoring the need for prompt diagnosis and aggressive management.12

BACTERIOLOGY CSF shunt infections are typically caused by low-virulence organisms. The most commonly cultured agent is Staplylococcus epidermidis, which accounts 50 percent of all shunt infections; Staplycococcus aureus, the next most commonly cultured agent, accounts for 25 percent of all shunt infections. Gram-negative, anaerobic and mixed infections account for approximately 5 to 10 percent of shunt infections. Gram-negative infections are associated with the highest mortality. Patients with CSF shunts have a higher risk of developing meningitis from typical pathogens (e.g., Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis) compared to the general population. This increased risk may be due to disruption of the blood-brain barrier by foreign material.

CLINICAL FEATURES The clinical presentation varies with the virulence of the organism and the severity of the infection. Typically, patients will present with obstructive and possibly meningeal symptoms, including mental status changes, headache, nausea, vomiting, and irritability. Fever, meningismus and abdominal pain may also be present. Unfortunately, these signs are not universally present. In fact, the finding of fever is highly variable and meningismus may only be present in only a third of patients with shunt infection.2 Abdominal pain may be the predominant symptom in patients with ventriculoperitoneal shunts. Swelling, erythema, and tenderness along the site of the shunt tubing are highly suggestive of external shunt infection.

EVALUATION To exclude CSF shunt infection, a shunt tap is required ( Fig 2.28.-..1. ) (see evaluation of shunt malfunction). This procedure should be performed by a neurosurgeon or by an emergency physician only after consultation with a neurosurgeon. A traditional lumbar puncture often misses CSF shunt infection and has no meaningful role in the evaluation when infection is suspected.

The cell count of patients with infected CSF shunts usually reveals an elevated leukocyte count, elevated protein, and normal glucose levels. Almost one-fifth of patients evaluated for shunt malfunction may have positive CSF culture despite normal CSF analysis. Non-CSF lab values are rarely helpful in diagnosing CSF shunt infection. CT scan and plain radiographs of the shunt (shunt series) are required to exclude mechanical shunt malfunction, which often coexists with shunt infection. 3 Abdominal ultrasound or CT scan are indicated if an abdominal fluid collection, pseudocyst, or abscess is suspected.

MANAGEMENT All patients with CSF shunt infection or suspected shunt infection require emergent neurosurgical consultation and admission. Most neurosurgeons advocate replacement of the infected shunt, external CSF drainage and administration of intravenous and intrathecal antibiotics. This combination of therapy has a 96 percent success rate. Until the infecting agent is identified, broad-spectrum antibiotics effective against typical pathogens are recommended (e.g., intravenous third-generation cephalosporin and aminoglycoside, plus intravenous or intrathecal vancomycin). Meningitis caused from typical pathogens has been successfully treated with antibiotics alone.

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