- Dependent on location of bur hole: When considering the removal of a shunt system with the concurrent insertion of an EVD, the surgeon must consider whether the EVD catheter will be placed through the same bur hole where the current shunt resides or if a new ventricular access will be necessary. If the previous shunt has been inserted using a precoronal access, then the head is oriented perpendicular to the floor. If the shunt has been inserted using an occipital access, then the head is turned 60 degrees to the opposite side, which will allow a comfortable angle for catheter insertion.
- Alignment for proximal catheter insertion: Insertion of EVD catheters follows the same basic principles and anatomical landmarks as shunt catheters. Individual anatomical variations, especially in children with congenital malformations, should be reviewed preoperatively in imaging studies, and changes should be planned accordingly.
- Changing proximal insertion site: The surgeon might choose to insert the EVD first through a different bur hole prior to removing the proximal catheter of the infected shunt. Some surgeons favor this approach on the grounds that it avoids excessive CSF lost through the tract left by the old catheter and ventricular collapse. It is also practical when the system to be extracted is in an unusual location, such as a ventriculoperitoneal shunt treating a Dandy-Walker cyst or a trapped fourth ventricle.
- Abdominal pseudocysts: The author’s strategy for a patient with this type of CSF collection is to externalize the distal catheter through an incision below the clavicle. At that time a sample of CSF is obtained from both the shunt reservoir and cyst (by aspirating from the distal catheter prior to its removal from the abdomen). The author recommends waiting for final cultures to define the fate of the shunt system. It is not unusual for the gram stains of the initial specimens to be negative but have bacteria, especially Staphylococcus or diphtheroids, ultimately grow in culture.
- Implications of multiorganism infection: Whenever more than one microorganism is identified during the initial workup, especially if one is gram negative, there should be a suspicion of a distal catheter perforating a bowel, bladder, or cul de sac. In this case an attempt should be made to detach the distal catheter from the rest of the system and remove it via a separate, distal incision to avoid contaminating the proximal part of the shunt system and the head wound.
- Removal of infected shunt: The shunt is usually removed by opening the cranial wound overlying the bur hole, as this will enable extraction of the proximal catheter, valve, and distal catheter with minimal dissection; it also allows the insertion of an EVD catheter immediately after shunt extraction.
- Insertion of EVD: In most cases, children with hydrocephalus and ventriculitis require external drainage during antibiotic treatment, and therefore an EVD should be placed at the time that the infected hardware is removed. There seems to be little evidence against using the same incision and shunt tract into the ventricle when placing an EVD in an infected patient.
- Importance of observing catheter length: At the time of EVD insertion, depending on the ventricular size and anatomy, the catheter can be placed with or without a stylet. However, catheter length should be monitored to ensure adequate drainage.
- Management of bowel perforation by distal catheter: On the rare occasion when an infected shunt is extracted and the distal catheter is found to be impregnated with feces (implying an unsuspected bowel perforation), the author prefers to irrigate and close the wound and later choose another EVD insertion site.
- Secure distal exit site against accidental breakage and disconnection: After the EVD catheter is in the ventricle and CSF samples have been obtained along with swab specimens from any secretion observed, the catheter is exteriorized and secured to the skin using silk sutures to create a semi-circle that precludes pulling out the catheter by diverting the angle of traction. Other techniques for catheter anchoring to the skin have also been described elsewhere. Silk sutures are preferred to nylon for attaching the EVD catheter, as nylon tends to cut through the skin especially after 10 days of EVD placement. A layer of transparent dressing can be placed over this setup; however, great care must be taken in removing it whenever the catheter and associated wound require cleaning.
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