CSF Shunting Procedures

CSF shunts are inserted for the relief of a variety of hydrocephalic states and pseudotumor cerebri. Hydrocephalus can be communicating or noncommunicating. In a noncommunicating hydrocephalus, CSF egress from the ventricular system is obstructed. Such obstruction can occur as a result of blood or infection in the ventricular system

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The ventriculoperitoneal shunt is the most commonly used device. Generally, a catheter is inserted through a bur hole into the frontal horn of the lateral ventricle on the nondominant (usually the right) side. A reservoir is placed subcutaneously adjacent to the bur hole, and the drainage limb passes through a subcutaneous tunnel to a point near the epigastrium, where it is inserted into the peritoneal space through a very small laparotomy. A moderate degree of muscle relaxation may be helpful. A distended stomach can result in an inadvertent "gastrostomy." Occasionally, most commonly in pediatric patients, there may be obstruction at more than one level in the ventricular system, and a so-called double-barreled shunt becomes appropriate. In this instance, there are two proximal ends: usually one in the lateral ventricle and one in the fourth ventricle. This latter procedure is generally performed in the prone position, whereas most ventriculoperitoneal shunts are performed in the supine position.

Occasionally, when a communicating hydrocephalus is present, a lumboperitoneal shunt is inserted. The patient is placed in a lateral position, and a catheter is inserted into the lumbar CSF space with the use of a Tuohy-type needle. The catheter is then tunneled subcutaneously around to the anterior abdominal wall and inserted into the peritoneal space through a small laparotomy.

In the past, ventriculoatrial shunts were used, although they have largely been abandoned because of the occurrence of pulmonary embolism. For these shunts, the noncerebral end is inserted into the venous system through the jugular vein. The atrial location of the noncerebral end is confirmed by using the same ECG technique that is used to place VAE recovery catheters (see the section "Venous Air Embolism").

Anesthetic Management

Invasive monitoring is not generally required. The anesthetic technique should be chosen to avoid further increases in ICP. Moderate hyperventilation (PaCO₂ of 25 to 30) is customary. However, aggressive ICP reduction measures are not warranted because collapsing the ventricles may render them more difficult to "hit" with the ventricular catheter. The procedure is usually performed in the supine position, with the table turned 90 degrees and the head turned toward the anesthesiologist. Blood pressure may drop abruptly (as brainstem pressure is relieved) when the ventricle is first cannulated. Infrequently, brief pressor support is required. Burrowing the subcutaneous tunnel can produce a sudden painful stimulus. Postoperative discomfort is only minor.

Unlike most neurosurgical patients, shunt patients are often nursed flat after their procedures in an attempt to prevent excessively rapid collapse of the ventricular system. Empirically, there is a small incidence of subdural hematoma after shunting, and tearing of the bridging veins at the time of rapid brain shrinkage is a suspected cause.

Pediatric Ventriculoperitoneal Shunts

Shunts are probably more commonly performed in children than adults. Common indications are hydrocephalus occurring in association with meningomyelocele, neonatal intraventricular hemorrhage, and posterior fossa tumors. Although one can never be casual about the management of these patients, open fontanelles seem to provide some margin for error in younger patients, and in addition, palpation of the fontanelles provides on-line trend monitoring of "ICP." In spite of the theoretical considerations, induction with volatile anesthetics is empirically well tolerated, even in children with closed fontanelles. However, we would avoid that induction technique in a child who was already stuporous. When an intravenous line is available, we generally use a propofolrelaxant induction sequence. For children in whom cannulation of a peripheral vein cannot be accomplished readily, induction with inhaled sevoflurane is a common approach, with initiation of controlled ventilation by bag and mask as rapidly as possible. If in the absence of sevoflurane, halothane were used for induction, immediately after loss of consciousness we would generally change to isoflurane and control the ventilation manually. After establishing controlled ventilation, an ideal course at this point is to establish an intravenous line, administer a muscle relaxant (with or without atropine according to your biases) and perhaps an induction drug, and intubate the patient in these optimal circumstances. Anesthesia is most commonly maintained thereafter with 60% to 70% nitrous oxide, mechanical hyperventilation, and isoflurane or sevoflurane as required. For children in excess of 6 months of age who were not stuporous at the outset, we commonly administer 2 to 3 µg/kg of fentanyl in the belief that this procedure is not entirely pain-free postoperatively and, in addition, that a smoother emergence can be accomplished with a narcotic background.