1. Maintaining cerebral perfusion pressure is essential in these patients. While one may desire some hypotension (particularly for AVMs or aneurysms) to minimize bleeding and avoid potential rupture of these neurovascular lesions, it is just as important to avoid ischemia in the surrounding brain tissue. Therefore, maintaining adequate perfusion to the brain tissue is critical.

2. Adequate intravenous access is necessary as these patients can lose blood very quickly, should a rupture of the vessel occur intraoperatively.

3. Many of these cases are being performed in interventional radiology. Whether it be for coiling of the lesion or serial embolizations prior to a surgical intervention, the anesthetic plan may actually need to take into account the fact that multiple anesthetics will be performed on the same patient on consecutive days. This can affect the intravenous access placed or the hemodynamic monitors used. Also, given the fragility of the lesions prior to and after both the embolization and surgical procedure, the numerous inductions and emergences from anesthesia, and the sedated period in between procedures, the anesthesiologists involved in the care must be very careful to avoid any significant swings in hemodynamics, as the shearing forces could lead to rupture of any of the lesions mentioned above.

I. Background

A. Cerebrovascular disease (CVD) is rare in pediatric patients and typically presents as either hemorrhagic or ischemic stroke. The underlying vascular anomalies that can result in stroke can be categorized as the following:

1. Structural changes in pre-existing blood vessels, that is, aneurysms or arterial dissections.

2. Pathologic vascular structures including arteriovenous malformations (AVMs), vein of Galen malformations (VOGMs), arteriovenous fistulas, and cavernous malformations (CMs)/hemangiomas.

3. Progressive arteriopathies such as moyamoya syndrome or heritable arteriopathies.

II. Patient assessment

A. Afflicted patients will present with headaches, seizures, cognitive deficits, focal neurologic deficits (weakness, numbness, or visual field problems), previous transient ischemic attacks (TIAs), or cerebral vascular accidents (CVAs). However, most patients with neurovascular lesions have no symptoms or specific physical findings on examination. Associated systemic illnesses such as systemic lupus erythematosus (SLE), congenital cardiac disease, high-output cardiac failure, and illicit drug use such as cocaine are associated with neurovascular lesions.

B. A systolic bruit over the eye, head, or neck (which is present in 15% to 40% of patients with an AVM or carotid dissections) may be detectable. AV shunts may be associated with tachycardia, cardiomegaly, and cardiac failure, especially in infants with a VOGM.

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CLINICAL PEARL

In general, the perioperative management of pediatric patients undergoing imaging studies and endovascular or surgical correction of their vascular anomalies should focus on optimizing cerebral perfusion and oxygen delivery to the brain tissue. Anesthetic management is focused on maintaining hemodynamic stability to assure adequate cerebral perfusion. However, it may be complicated by intracranial hypertension. Since the surgical resection of these lesions can be associated with significant blood loss, these patients require adequate intravenous (IV) access and invasive hemodynamic monitoring. Maintaining intravascular volume is key for these goals. Therefore, blood products should be available to replenish sudden massive blood loss. Hypotension from hypovolemia can be temporized with vasopressor agents such as ephedrine, phenylephrine, or infusions of dopamine, norepinephrine, or epinephrine. Alternatively, hypertension needs to be avoided as well, as one would not want to rupture these delicate vessels prior to, during, or after surgical repair. If an endovascular procedure be performed in the interventional radiology (IR) suite, the anesthesia team should be prepared that there may need to be an emergent surgical intervention should any complications occur during any IR procedure.

III. Radiographic studies

A. Several different modalities are used to aid in the diagnosis of neurovascular lesions.

1. Intracranial ultrasonography: Can be used as an initial, nonurgent screening test in infants with an open fontanel and for detecting hemorrhage, hydrocephalus, large infarcts, or lesions such as an AVM or VOGM.

2. Duplex ultrasonography is useful in the diagnosis of an extracranial carotid dissection.

3. Computerized tomography (CT)/computerized tomography angiography (CTA): CT is typically the initial study for any patient with neurologic symptoms and diagnosing hemorrhage, delayed stroke, or large vascular lesions. CTA is excellent for the evaluation of an AVM, aneurysm, and moyamoya disease.

4. Magnetic resonance imaging (MRI)/magnetic resonance angiography (MRA) is useful for the evaluation of stroke with diffusion-weighted images (DWIs), CMs (susceptibility imaging), and most vascular lesions.

5. Digital subtraction angiography (DSA) is the gold standard for all vascular lesions except CMs.

B. Pediatric anesthesiologists frequently anesthetize these patients with neurovascular lesions for an imaging study to obtain a definitive diagnosis. Due to reasons such as the invasiveness of the CTA to obtain venous and arterial access and to obtain optimal images, and the length of time a patient needs to stay still for an MRI, anesthesiologists are needed to keep the patients still for optimal images while maintaining a patient’s normal physiology during a general anesthetic.

C. For MRI, these anesthetics can typically be performed under a deep sedation. Should the patient have a full stomach or other complicating conditions, the anesthetic for MRI may be done under general anesthesia. A discussion between the primary service and radiology service can help determine the type of anesthetic necessary. If deep sedation is chosen, typically, agents such as propofol or dexmedetomidine can be used. General anesthetic requires that airway control be secured by either a laryngeal mask airway (LMA) or endotracheal tube (ETT). The usual concerns for performing an anesthetic in the MRI suite (different sets of monitors, equipment, distance from the patient, and lack of familiar resources available in the main operating room) must be considered for these imaging studies. Hemodynamic stability should be maintained in patients with neurovascular lesions, since hypo- and hypertension can precipitate ischemia and hemorrhage respectively. Typically, a deep sedation provides a smoother hemodynamic course.

D. CTA can also be performed under a deep sedation with local anesthesia. However, an uncooperative infant or child will require a general anesthetic. Furthermore, interventional radiologists may need episodes of apnea or hypercarbia to optimize the images during angiography. Apnea or hypoventilation can be achieved under general anesthesia.

IV. Arteriovenous malformations

A. AVMs result from improper formation of the arteriolar-capillary network that provides a direct connection between arteries and veins in the brain without intervening capillaries. This produces low resistance and leads to a high-flow shunt. They can occur in the cerebral hemispheres, brainstem, and spinal cord. The embryonic origins of these malformations are unclear. Functional neural tissue does not reside within the lesion. Surrounding tissues are deprived of blood supply and nutrients.

1. Anatomically, these malformations consist of large arterial feeding vessels, dilated communicating vessels, and large draining veins carrying arterialized blood.

2. Cerebral damage can result from AVMs due to the steal phenomenon, ischemia, hemorrhagic infarct from thrombosis, cerebral atrophy, or alterations of flow during surgery.

3. Saccular dilation of the vein of Galen (see the following text) may present later in infancy or childhood with hydrocephalus secondary to obstruction of the aqueduct of Sylvius.

4. In the pediatric population, the most common presentation is an intracerebral bleed, a seizure and hydrocephalus, or congestive hearing failure (rarely) in the neonatal period.

a. Malformations not large enough to produce congestive heart failure (CHF) usually remain clinically silent unless they cause seizures or stroke, or until the acute rupture of a communicating vessel results in subarachnoid or intracerebral hemorrhage. Initial presentation is typically hemorrhage (80% to 85%) with an associated mortality of 25%. They present as seizures, headache, or focal neurologic deficits (from either mass effect from bleeding or from cerebral ischemia due to diversion of blood to the AVM from the normal cerebral circulation, known as the “steal” phenomenon). Ninety percent of AVMs occur supratentorially, most commonly in the distribution of the middle cerebral artery.

5. Mortality seems to be higher in younger patients as compared to adults.

6. If amenable, treatment is usually embolization or radiation of deep AVMs, surgical excision usually for more superficial AVMs that are located in noneloquent areas of cortex, or some combination of these modalities (with the intent of decreasing the size and blood flow through the AVM during embolization, leading to a solid brittle mass that can then be surgically resected later). The purpose is to eliminate the malformation from the cerebral circulation in order to prevent intracranial hemorrhage. If surgically it is too difficult to approach, then treatment is with gamma knife over several months.

7. Rebleeding can occur approximately 6% during the first 6 months and then 3% per year afterward.

8. Sometimes, emergency surgery is necessary for increasing intracerebral hematoma that can be a significant risk for brain herniation, so a ventricular drain may be placed to treat acute hydrocephalus.

B. Anesthetic considerations

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1. Anesthetic management for embolic procedures in the IR suite usually involves a standard general anesthetic with neuromuscular blockade and secure IV access. The anesthesiologist should be knowledgeable about the types of embolic agents that will be used and their potential complications.

a. Bleeding, especially from the femoral arterial puncture site (which cannot always be visualized), should always be a consideration. This is especially true as the patient will be heparinized during the time the sheaths and catheters are in place.

b. Fluid overload can occur due to the large amount of contrast agents administered, especially in a young infant who may already be in high-output CHF. Newborns with CHF may be receiving several inotropic agents. It is possible to get some idea of the degree of cardiac compromise in newborns by obtaining a detailed feeding history—frequency, length of time per feeding, amount, respiratory distress during feeding, and so on.

c. One should always be prepared for an emergency craniotomy should a vessel rupture occur.

(1) If rupture occurs, one may have to induce hypotension in order to minimize the blood loss. If an occlusion occurs during embolization, then blood pressure should be augmented (with or without thrombolysis) to increase perfusion distally. Blood products should be readily available and adequate IV access obtained prior to any embolization.

2. If the AVM is amenable to surgical resection, then a craniotomy is performed in the operating room. Similar to other craniotomies, the anesthetic goals center on optimizing cerebral perfusion pressure (CPP) and oxygen delivery, which includes maintaining adequate mean arterial pressure. Avoiding large swings in blood pressure is the key to avoid any rupture of the AVM [1,2].

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a. Again, being prepared for a sudden loss of blood is essential. Multiple IV lines and an arterial line are helpful.

b. Techniques to reduce cerebral edema such as moderate hyperventilation or osmotic diuresis may aid in providing an optimal surgical field.

c. Titrating the anesthetic to a wake-up that avoids significant hypertension and allows the neurosurgeon to perform a complete neurologic examination shortly after surgery is ideal.

3. Currently, the treatment for AVMs involves embolization in IR prior to a surgical excision. The intent is that embolization will lower the high-flow circulation through the AVM, making the surgical resection less bloody. This also allows the tissue around the AVM to adjust gradually to the change in perfusion in that region.

4. Inhalational agents and IV agents have been used safely for the anesthetic for these lesions. Both decrease the cerebral metabolic rate of oxygen consumption (with the exception of ketamine). Inhalational agents can cause vasodilation whereas IV agents cause vasoconstriction. Theoretically, vasodilators may produce the steal phenomenon while the vasoconstrictors can lead to inverse steal and potentially protect the brain or prevent damage. There is no evidence favoring one or the other in terms of outcome for these patients. Likely, the most important thing is to maintain normotension and avoid large swings in blood pressure.

5. Since seizures are a common presenting symptom in these patients, they are often on anticonvulsant therapy. Therefore, the anesthesiologist needs to take into account the considerations previously mentioned regarding these drugs, in particular the need for increased doses of narcotics and muscle relaxants to maintain an adequate depth of anesthesia and muscle relaxation. Furthermore, the anticonvulsants should be continued in the perioperative period.

C. Perioperative complications

1. Hydrocephalus can result from subarachnoid blood and is initially managed with an external drain to lower CSF volume and to monitor ICP. Approximately one-third of all SAH patients will ultimately require ventricular shunt.

2. Rehemorrhage or stroke can occur from a faulty clip placement or a residual AVM. Residual lesions should be investigated with postoperative vascular imaging if possible and treated with evacuation of a clot if necessary and/or repositioning of the vascular clip.

CLINICAL PEARL

Normal perfusion pressure breakthrough (NPPB) can occur in a small number of patients with high-flow AVMs and results in postoperative parenchymal hemorrhage and cerebral edema from markedly increased blood flow in cerebral vessels (that were previously hypoperfused) after embolization or surgical resection of the AVM. NPPB should be anticipated after treatment of a high-flow lesion and can sometimes be avoided via staged embolizations prior to surgical resection and maintenance of normal to slightly low blood pressure postoperatively.

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