Pediatrics Mary Lou Steward HE management of the pediatric patient for interventional neuroradiology procedures can present problems for each member of the team. For the neuroradiologist, access to the femoral artery or femoral vein, or a superficial vascular anomaly can be technically very difficult. The size of the small intracranial vessels may make passage of the microcatheters impossible. For the anesthesiology team, there may be several logistic problems. Intervention neuroradiology requires the skill of subspecialty neuroradiologists and a sophisticated bipolar angiography machine. This may only be available at an adult hospital and, therefore, some special arrangements must be made. For treatment in our unit, the patient is admitted to the local children's hospital and then transported to our hospital with a pediatric ICU nurse in attendance. After the procedure is finished, and the patient is stable, he/she is transported by the ICU team back to the children's hospital ICU. This requires a great deal of cooperation between the interventional neuroradiologist and the pediatric neurosurgeon. In children with intracranial vascular lesions, as in adults, interventional neuroradiotogy has either replaced or has become an adjunct to surgery. Although rare, pediatric intracranial aneurysms, when they do occur, are managed with coil embolization. Arteriovenous malformations (AVMs) are much more common than intracranial aneurysms in the pediatric population. For these patients, interventional neuroradiology may require several treatment sessions. As with adults, polyvinal particles or various synthetic glues are used to occlude the nidus and feeding vessels of the AVM. The goal of therapy, as .described elsewhere in this
From the Department of Anesthesiology, University of Southern California, Los Angeles, CA. Address reprint requests to Mary Lou Steward, MD, FRCP (c), LAC+ USC Medical Center, Department of Anesthesiology, 1200 Nol~h State St. (14-901), Los Angeles, CA 90033. Copyright 9 2000 by W.B. Saunders Company 0277-0326/00/1904-0013510.00/0 doi: l O.l O53/sa.2000.17798
issue, is either complete obliteration of the AVM, to reduce the size of the AVM to less than 3 cm so that the lesion is amenable to gamma knife treatment, or to decrease the size of the AVM so that blood loss during surgical excision of the lesion can be minimized. It has been recommended by some authors 1 that deliberate hypotension be used when the neuroradiologist is embolizing an AVM. This will allow a decrease in the velocity of cerebral blood flow across the lesion and thus allow more precise deposition of the glue within the AVM. One lesion that occurs in the pediatric population is the vein of Galen malformation (Figs 1 through 4). These lesions are characterized by venous hypertension and hydrocephalus due to obstruction of the aqueduct of Sylvius. In a study of a series of patients, Vinuela 2 noted that this lesion presented with congestive heart failure in 53.6%, seizures in 21.4%, hydrocephalus in 14.3%, and intraventricular hemorrhage in 10.7%. Computed tomography scan and magnetic resonance imaging (MRI) demonstrate an abnormal dilation of the midline venous structures of the cerebrum. Because there is no capillary resistance bed, this lesion acts as a high-flow shunt, which can result in severe cardiac failure in the newborn. The arterial supply to the surrounding brain tissue is also compromised. Brain atrophy, hydrocephalus, intracerebral calcification, or hemorrhage may be present and may lead to long-term neurological morbidity. In the series reported by Vinuela, a combined transfemoral arterial and venous approach to arterial and venous embolization was used. They obtained complete occlusion in 46.4%, immediate improvement in 82.1%, and good long-term results in 60.7%. They had five deaths in their series, which compares very favorably with the high morbidity and mortality rates for open surgery. The younger the patient presents with the lesion, the greater the risk of surgical treatment. This is because the neonate often has biventricular congestive heart failure, the surgery is technically more difficult, and the blood loss is often excessive. The effect of this complex congenital arteriovenous
Seminars in Anesthesia, Perioperative Medicine and Pain, Vol 19, No 4 (December),2000: pp 304-308
Fig 1. AP view of the brain of a 6-month-old patient with vein of Galen abnormality.
Fig 3. Lateral view of same patient showing early stages of coil embolization.
connection is the premature dumping of arterial blood into the venous circulation, because there is no capillary resistance bed. This hyperdynamic state frequently causes cardiac failure and death in the first few days. A lesion which resembles the vein of Galen malformation from a pathophysiologic point of view is the dural arteriovenous fistula (Fig 5). These lesions can be embolized with coils and/or glue and may require several sessions to c o m -
pletely occlude the lesion. It is suggested 1 that during embolization of a dural arteriovenous fistula, hypercapnia should be induced. This increases the intracranial circulation, cerebral blood volume and rate of venous return from the intracranial space, and may protect the intracranial veins from any embolic agent that may drain toward these veins.
Fig 2. Lateral view of same patient,
Fig 4. AP view showing complete embolization of the vein of Galen.
MARY LOU STEWARD ANESTHESIA CONSIDERATIONS IN PEDIATRIC PATIENTS
Fig 5. CT scan of the same patient taken at completion of embolization, showing intracranial hemorrhage from spontaneous rupture of the lesion.
We have treated a 3-year-old patient who required 10 sessions of embolization to an AVM (with over 600 coils and glue) before he was able to proceed to surgery (Fig 6). A craniotomy was performed, and the entire residual lesion was safely removed. AVMs of the spinal cord and surrounding tissues also occur in the pediatric population. The risk of neurological damage during the procedure is very high in these patients, and monitoring of neurological function is critical during embolization. This may not be easy in a young and uncooperative patient. AVMs may involve the face and neck. Treatment is either by embolization via the transfemoral route or by percutaneous injections of their endovaScular space using a sclerosing fluid. This destroys the endothelium and eventually obliterates the endovascular space. Posttreatment swelling of the area can occur, and it is important to ensure that this will not compromise the airway. AVMs of the face may cause troubling epistaxis. We have treated a 12-year-old boy with an AVM involving his nose. He received several treatments using glue shots using catheters via the femoral artery and vein until the lesion was reduced in size for gamma treatment. Several months later, however, the AVM recurred and he presented with persistent epistaxis. Percutaneous injections of several areas were then performed in order to decrease the incidence of eplstaxis.
There are several important considerations. First, these procedures take place in the interventional neuroradiology suite, which may be quite a distance from the main operating room. The rooms tend to be cold to protect the very sophisticated x-ray machines. As a rule, the cases require general anesthesia with endotracheal intubation, because it is difficult to get these patients to cooperate. Because many of these lesions require several treatment sessions, with repeated anesthetics and ICU admission, these patients become progressively less cooperative. It is very important, therefore, to be as prepared as possible before anesthetizing these patients. Initially, it is essential to obtain a detailed history from the parents. Examine any previous anesthesia records and discuss with the parents the induction method that may be appropriate. Check the size of the endotracheal tube that was used for the previous anesthetic and the effect of any premedication that may have been given. If the child is old enough, he or she should be allowed to discuss the various options. Drug allergies and current medications must be documented. If Dilantin is on the list, consider whether it is necessary to have a blood level done. We generally order a pre-anesthetic hemoglobin, coagulation screen, and any other specific tests that may be indicated.
Fig 6. AP view of the brain of a 4-year-old with a complex dural fistula showing the result of many glue embolizations.
PEDIATRICS If the lesion is to be occluded by glue embolization in an infant up to 2 years of age, a preoperative echocardiogram is usually obtained. If there is an intracardiac shunt, glue particles could potentially cross to the left side of the heart and prove to be fatal if they reach the cerebral circulation. In such cases, therefore, embolization may be contraindicated. If the child has been an inpatient, he/she may have an IV line already established. If not, the intravenous line can be started before or after induction of anesthesia depending on the child and the anesthesiologist. Patients younger than 6 years of age may be sedated with oral midazolam (0.5 mg/kg) premixed with a cherry syrup. An alternative is to place an eutectic mixture of local anesthetics (EMLA) cream on the skin 60 minutes before starting an IV line and giving IV midazolam as a premedication. It is preferred to have a wellsedated child to bring to the neuroangiography suite and then leave the parents outside in the waiting room. However, some children are much more cooperative with their parents being present in the room for the induction. The standard of care for anesthesia is similar to that for the operating room. The following monitors are routinely applied: EKG, pulse oximeter, noninvasive blood pressure cuff, end-tidal CO 2 sampling, temperature, as well as a stethoscope. Because most of these patients will receive muscle relaxants to prevent any movement whatsoever during critical "road-mapping" or glue-depositing, a nerve stimulator is essential. A urinary catheter is inserted in almost every patient because the contrast dye has a diuretic effect, and also in high doses may cause renal tubular damage. Therefore, it is important to monitor urine output. Most of these cases are done by the transfemoral artery approach. A small cordis sheath is inserted and, from that, a direct arterial pressure tracing can be obtained. Unfortunately, when the microcatheters are inserted through the sheath, the tracing is dampened. However, it is not usually necessary to insert another peripheral arterial catheter. Somatosensory evoked potentials (SSEP) monitoring is used for those cases in which neurological function may be compromised. It is necessary therefore to select appropriate anesthetic drugs and concentrations that will have the least effect on this monitoring (see the article in this issue on "neurophysiologic monitoring," by Lai and Manninen).
307 Finally, most of these patients will receive systemic beparinization, which will be followed the with serial activated clotting time measurements. Induction of anesthesia is with intravenous agents (propofol or thiopental) if an IV line is already established or by inhalation with sevoflurane followed by the insertion of an IV cannula. A muscle relaxant is used to facilitate the insertion of the endotracheal tube. Listen carefully for bilateral breath sounds, and also check the position of the endotracheal tube by fluoroscopy of the chest. Narcotic analgesic drugs are added as required. This helps to minimize the concentration of inhalation agents used, which improves the quality of the SSEP monitoring. During the procedure, systemic heparinization is usually required. The dose of heparin used is 50 to 100 U/kg as a bolus followed by 50 U/kg of heparin every subsequent hour to obtain an activated clotting time three times normal. This may or may not be reversed at the end with protamine. During the embolization, there are several conceres. Because the room is cold, it is important to cover the patient with a forced air warming blanket to prevent hypothermia, especially in the very small patient. It is not easy to gauge the appropriate IV infusion rate, because the nenroradiologists need to continually perfuse their microcatheter in order to keep them patent. Blood loss is also difficult to judge and, during a long procedure on a small patient, this may be significant. Thus, it is important to check the hematocrit level during the procedure. In the very young child, the systemic blood pressure correlates reasonably well with the patient's intravascular volume status and is used as a guide to fluid therapy. Biplane angiography helps to limit the total dose of contrast dye injected. As mentioned in previous articles of this journal, the "road-mapping" feature allows the dynamic tracking of microcatheter advancement superimposed upon an angiogram. This also decreases the amount of dye used, but also means that during this time, the patient must not move. The total volume of Contrast dye used at any given treatment session is usually limited to 4 mL/kg. If this amount is reached, give 0.25 g/kg mannitol intravenously slowly to encourage diuresis and thus protect the renal tubules. The complications during these procedures are often immediate, profound, and difficult to treat. Intracranial hemorrhage can result from the cathe-
308 ter perforating the vessel or the aneurysm and/or fistula spontaneously rupturing. If a vital artery is accidentally embolized, ischemia can result and produce a severe neurological deficit. Vasospasm of these arteries as a result of stimulation by the microcatheters can also lead to post embolization neurological damage. Also, it is possible for the microcatheter to remain adherent to the vessel during glue embolization if the catheter is not removed quickly enough. Other concerns are the potential reaction to the contrast media. In this case, treat the patient with IV diphenhydramine and steroids. Also, in long and multiple procedures, there is the risk of radiation exposure hazard to the patient and the personnel in the angiography suite. After embolizafion, the goal is to have the child awake and extubated, so that the neurological status can be assessed. If there has been an intratreatment complication, it may be necessary to institute a regime for brain protection. The current practice is to leave the patient intubated and start a propofol infusion. If SSEP/EEG monitoring has been used,
MARY LOU STEWARD adjust the infusion rate to produce burst suppression on the EEG. It may be necessary to do a computed tomographic scan of the brain and even an emergency craniotomy in the operating room. Most patients are taken extubated and awake to the postanaesthesia room until they are stable enough to be transported to the pediatric ICU. It is important to order anti-emetics and analgesics because headache, nausea, and vomiting can occur after these treatments. Interventional neuroradiology has an important role in the treatment of pediatric vascular lesions. The optimum outcome of these treatment sessions depends on good communication and cooperation among the neuroradiologist, pediatric neurosurgeon, and pediatric anesthesiologist.
REFERENCES 1. Young WL, Pile-Spellman J: Anaesthetic considerations for interventional neuroradiology.Anaesthesiology80:427-456, 1994 2. Lylyh P, Vinuela F, Dion JE, et al: Therapeutic alternatives for vein of Galen vascular malformations. J Neurosurg 78:438445, 1993