Etiology of Hydrocephalus

The etiology of hydrocephalus as a risk factor for the development of infections has not been clearly shown. An association between the causal agent and a higher risk for shunt infection has rarely been found,^11,14 although a recent review described an association between obstructive hydrocephalus and rate of complications.¹⁵

Hydrocephalus following perinatal bleeding has been associated with a higher incidence of infection,¹⁶ but we could not establish such an association in our series of 964 operated patients.

Patient Age and Nutritional Status

Many reports stress the importance of age as a risk factor for infectious complications in patients who have a CSF shunt.^9,17 The risk of complications is mainly present in infants and elders. A multicenter study analyzing shunt complications in general found that younger children were at a higher risk of complications and malfunction; however, the study fails to specify whether these were infectious or obstructive.¹⁸

Nutritional status is yet another significant factor, as undernourished subjects seem to have a higher rate of infectious complications.¹⁹ Infant nutrition may also play an important role, and a lower incidence of infection has been described in breastfed infants.²⁰

Surgical Technique

The implantation technique of a ventriculoperitoneal or ventriculoatrial shunt is also extremely important. The absence of an appropriate strategy may turn a procedure normally representing low mortality and morbidity, and presumably requiring a short hospital stay, into a complicated procedure that eventually results in multiple reoperations, longer hospital stays, higher costs for the healthcare system, and potentially serious sequelae for the patient.

Shunt implantation is a procedure often performed by neurosurgical trainees who have inadequate experience in the technique; this factor may be critical for the development of postoperative infections.²¹

Many papers have shown that postoperative infection rates may be reduced by using a meticulous surgical technique.^7,11,22 Where possible, the procedure should be carried out in a dedicated neurosurgical operating room and be the first procedure of the day. The paramedic personnel involved in the procedure should be trained in prosthesis manipulation and instructed to maximally restrict circulation into and out of the operating room. Entrance to and exit from the operating room would only be allowed in emergency situations; where possible, the number of personnel within the operating room should be restricted to four professionals—an anesthesiologist, a nurse, a surgeon experienced in the management of hydrocephalus, and an assistant. Contaminated elements should be carefully placed away from the sterile sector of the operating room.

We recommend giving prophylactic antibiotic therapy at the time of anesthetic induction, as well as during the first 24 postoperative hours. A meta-analysis of recent reports showed the effectiveness of prophylactic antibiotic therapy in the reduction of infection rates.²³ The prophylactic antibiotic drugs scheme to be used should be designed after the bacterial flora prevailing in the healthcare site.

As far as individual patient care, the antiseptic procedure should be thorough; therefore, we recommend bathing the patient with povidone–iodine soap or a similar product 24 hours preoperatively. Immediately before the surgical procedure, the operating field must be washed three times with povidone–iodine soap using a nonsterile technique, and then the skin should be prepared another three times with povidone–iodine solution using a sterile technique. Placement of sterile fields should be meticulous and should try to expose the surgical area only, which should be covered with sterile drapes impregnated in iodoform (3M Ioban 2 Antimicrobial Incise Drapes EZ). Unnecessary surgical steps should be avoided to shorten the length of the procedure as much as possible.

The valve not only should suit the patient’s needs but also should be a device with which the surgical team is accustomed to working.

Many studies have investigated the association between antibiotic-impregnated shunt catheters and risk of infection. In vitro results²⁴ reported antibiotic-impregnated catheters afford a lower colonization risk, but reports of studies conducted in humans showed controversial results. Some authors stress the contribution of these devices to lower postoperative infection rates and thus recommend them as an effective tool.^25,26 Other reports have found no significant infection rate differences in patients who underwent the implantation of antibiotic-impregnated catheters.^23,27 This kind of devices could be used in patients with a history of previous infection or in high-risk cases, but regardless of the circumstance, the previously described perioperative care steps should be followed carefully.

Silastic exposure to room air must be minimized. For this reason, the sterile container should be opened exactly at the moment of implantation.

We recommend using forceps for implantation to avoid manipulation of the shunt system. Intraoperative preparation with povidone–iodine is useful, and some authors suggest immersing the shunt in a gentamicin solution bath.¹¹ The implementation of this kind of protocol has already been described by other authors^7,11,22 and proved to have high efficacy in preventing infection.

Presentation and Clinical Features of Shunt Infection

Presentation of shunt infections is highly variable, depending on the causal agent, the site of infection, and patient age. Many patients remain asymptomatic,²⁸ whereas others are oligosymptomatic or show signs and symptoms of increased intracranial pressure due to shunt malfunction. In neonates, clinical features of shunt malfunction include bulging fontanelle, irritability, vomiting, fever, and feeding difficulty. In older children and adults, the signs and symptoms tend to be nonspecific, though fever, headache, vomiting, meningism, and abdominal pain may suggest shunt infection. Up to 50% of shunt malfunctions may be explained by an underlying infection.²⁹

Occasionally, shunt infection signs are seen at the distal end, with abdominal symptoms that may vary from nontender focal peritoneal fluid collections to acute abdomen. The finding of abdominal fluid collections or pseudocysts is considered by many authors to be a sign suggestive of infection in patients with ventriculoperitoneal shunts,^30,31 although cystic fluid cultures often test negative.³² Early diagnosis of this complication by means of an abdomen computed tomography (CT) scan (Fig. 97-1) affords an effective management by externalizing the catheter, removing the shunt or re-placing the peritoneal catheter laparoscopically.^33,34

FIGURE 97-1 Oral and intravenous contrast-enhanced CT scan of the abdomen and pelvis. A large fluid collection (pseudocyst) is seen. Note the catheter inside the collection.

Infections associated with ventriculoatrial shunts are usually more severe and may cause bacteremia with a subsequent hemodynamic involvement on account of the close link between CSF and circulating blood flow, which could result in the formation of thrombi at the catheter tip and thus lead to endocarditis or thromboembolic events. Shunt nephritis is a glomerular disease produced by antibody deposits in the renal glomeruli and the production of complement, which is characterized by hematuria, anemia, liver and spleen enlargement, and nephrotic syndrome. Although shunt nephritis has a low incidence, it should be considered a potential diagnosis in patients who have a ventriculoatrial shunt.³⁵

Infections caused by skin organisms may present with redness and edema along the length of the shunt, wound dehiscence and shunt exposure, or purulent discharge through the wound (Fig. 97-2). This kind of infection is commonly external and occurs in neonates when CSF accumulates, particularly when CSF fistulas are present.³⁶ Thus, given the external nature of the infection in these cases, puncturing the valve would be inadvisable because it could lead to germ contamination of a sterile fluid.

FIGURE 97-2 Skin redness, hardening, and ulceration with a purulent background along the length of the shunt.

Mechanisms for Entry of Bacteria Into Shunts

Because skin organisms are the most commonly identified causal agents in shunt infection, colonization of prosthetic materials by direct inoculation at the time of shunt implantation usually constitutes the infection mechanism. This accounts for the early presentation of infections postoperatively. Skin wounds may also cause shunt colonization. Blood spread may occur in the setting of bacteremia and become particularly important when there is a ventriculoatrial shunt; it may also be seen in patients with neurogenic bladder. Finally, infections by gram-negative organisms in particular may show a retrograde spread as a result of bowel perforation.³⁷

Microbiology and Pathogenesis

CSF shunt infections are most commonly produced by certain low-virulence organisms present in skin flora. Common causal agents are coagulase-negative staphylococci, which are identified in 50% to 80% of shunt infections, together with coagulase-positive staphylococci.^38–40 Staphylococci can synthesize and secrete a mucoid substance called slime. Slime has been shown to be associated with vascular catheter infections as it adheres to plastic or polymeric materials and induces organism growth. It may also act as a mechanical barrier to systemic antibiotic action.^39,40 Although they are less common, gram-negative organisms are clinically important because they lead to higher morbidity and mortality rates.^37,41 Such anaerobic diphtheroid agents as the Propionibacterium acnes are a less common source of infection but should be equally regarded as a potential causal agent, because they are usually found on the skin and can contaminate shunts with few signs and symptoms.⁴¹

Diagnosis

CSF sampling for culture is mandatory to establish the diagnosis of infection.

Diagnostic criteria for shunt infection include the following:^42–44

Wherever possible, and depending on the type of shunt that has been implanted, the sample should be obtained from the valve reservoir. CSF culture is a key element for diagnosis; because of the common presence of low-virulence organisms, cultures should be kept for a long time to allow identification of slow-growing organisms.⁴⁵ CSF physical and chemical properties may raise clinical suspicion; CSF pleocytosis (particularly when neutrophils predominate), along with increased CSF protein levels and decreased CSF glucose levels, are suggestive of an ongoing bacterial infection.⁴⁶ Leukocytosis, erythrocyte sedimentation rate (ESR) elevation, and increased C-reactive protein levels may also prove useful for diagnosis (we found that ESR elevation is also useful in adults).

Infection may initially present with redness and/or skin hardening over the shunt area. In these cases, sampling from this area should be avoided.

Imaging techniques such as brain CT scans, as well as shunt x-rays and abdominal ultrasound or CT scans, are ancillary investigations that may prove useful to rule out malfunction or abdominal cysts.

Treatment

Controversy exists over what constitutes the best treatment for ventriculoperitoneal and ventriculoatrial shunt infections. Discussion is raised by whether the system should or should not be removed, since the ventricular catheter may adhere to the choroid plexus and removing the catheter may lead to intraventricular bleeding. Other factors to be taken into account when removing the shunt are patient dependence on the system and potential increase of intracranial pressure. CSF drainage should be ensured at the time of removal. Placement of an external ventricular drainage is associated with a risk for overinfection. Consequently, some authors suggest the implementation of less invasive treatment options, namely, intravenous and/or intrashunt antibiotic therapy.⁴⁷ Intravenous antibiotic therapy with shunt removal and CSF external drainage or ventricular punctures followed by reimplantation of the shunt when the CSF is sterilized has proved more effective in patients with shunt infection.⁴⁸ This is the most widely accepted procedure and the only one whose effectiveness has been demonstrated in a prospective randomized study comparing treatment options and a follow-up study.^49,50 Other studies have also shown the success of this treatment option,^51–54 which is reportedly close to 95%, with the lowest associated morbidity and mortality rates.⁴⁸

Bacteria such as staphylococci produce vitronectin, a substance that mediates bacterial adhesion to the catheter, preventing antibiotic action and making shunt removal unavoidable.⁵⁵ Some reports have shown a high cure rate when direct replacement of the shunt is performed and no external drainage is used before the replacement procedure.⁴⁸

Once a microbiologic diagnosis of infection has been established, management should consist of broad-spectrum systemic antibiotic agents, bactericides, and intravenous antibiotic agents; the shunt must be removed, and either an external ventricular drainage system must be placed or repeated ventricular punctures must be performed (in patients with bulging fontanelle). Once three CSF cultures test negative, the external drainage system should be removed and a new shunt should be implanted at a different location.

The duration of intravenous antibiotic therapy should be decided case by case because there are no defined protocols in this regard. In our experience, 14 days of intravenous antibiotic therapy are enough if there is no overinfection associated with the external ventricular drainage system.

When intravenous antibiotic therapy does not provide successful control of the infection (persistence of positive cultures), the intrathecal route may become an administration alternative (Fig. 97-3).

FIGURE 97-3 Treatment algorithm for shunt infections.