Red Flag	Indications
Apnea	Documented by sleep study, strong clinical history, or on an apnea monitor
Unstable cardiac disease	Cyanotic, depressed myocardial function, or significant stenotic or regurgitation lesions
Respiratory compromise	Recent (<8 weeks) pneumonia, bronchitis, asthma, or respiratory infection
Craniofacial defect	Potential for difficult airway
History of a difficult airway
Active gastroesophageal reflux or vomiting	In poor control, with or without medical or surgical treatment
Hypotonia and lack of head control	Patient may not be able to maintain own airway without assistance
Allergies to barbiturates	Usually the mainstay of a sedation protocol; also allergies to other sedatives to be administered
Prior failed sedation	Unable to be sedated or unsuccessful imaging study because of excessive movement
Tremors	Unlikely to be ablated with sedation

Because gastroesophageal regurgitation is common in infants, a detailed clinical history should be taken with regard to the incidence and timing of the regurgitation. If the reflux is predictable (i.e., only associated with mealtimes or soon thereafter) infants are usually approved for procedural sedation. Fasting guidelines are adjusted to minimize the risk of reflux. For example, if the infant has refluxes within 2 hours of eating solid food but never after 3 hours, the fasting guidelines for this infant may be extended to 6 hours for solids.

Selection of Agents and Techniques

The selection of an anesthetic technique in an extramural location depends on the patient’s underlying medical condition, age, drug tolerance, and anticipated procedure. The airway management may be influenced by the procedure itself, anticipated postprocedure course (e.g., intensive care unit [ICU] or postprocedure intubation) and past anesthetic course (e.g., difficult intubation). The assistance of an anesthesiologist is often sought when sedation administered by the radiologist has failed in the past; it is important to be aware that parents and radiologists may have the expectation that anesthesia will provide ideal conditions and guarantee successful completion of the procedure (Hubbard et al., 1992).

Premedication has many purposes: the relief of anxiety, easy separation from parents, sedation, analgesia, amnesia, reduction of salivary and gastric secretions, elevation of gastric pH, and decreased cardiac vagal activity. Medications should be adjusted to the psychological and physiologic condition of the patient and family. Parent-present inductions may be offered when the presence of a parent has a calming effect on the child. In the event of potentially detrimental parent anxiety, premedication may be preferable to a parent-present induction (Kain et al., 2001).

Barbiturates may be useful as the sole method of providing sedation. Pentobarbital, for example, has the advantage of providing sedation, causes minimal respiratory and circulatory depression, and is rarely associated with adverse events (Karian et al., 2002). Barbiturates have no analgesic properties. They can produce paradoxical reactions, especially in children. No antagonist to barbiturates is available, thus dosing should be carefully titrated. IV pentobarbital by titration has been used successfully by radiologists while monitoring oral and nasal air flow, oxygen saturation with a pulse oximeter (SpO₂), end-tidal carbon dioxide, and cardiac rate and rhythm, with transient decreases in SpO₂ in up to 7.5% of patients; interventions have included stimulation and head repositioning (Strain et al., 1988; Rooks et al., 2003).

Other studies have described the use of pentobarbital both in the oral and IV forms (Chung et al., 2000; Mason et al., 2001a). For infants younger than 1 year of age, oral pentobarbital is more successful and carries a lower rate of adverse events compared with chloral hydrate (Rooks et al., 2003). The long half-life of pentobarbital (approximately 24 hours) requires careful and conservative recovery and discharge guidelines. The dosage of oral pentobarbital is 2 to 6 mg/kg and up to 9 mg/kg in patients who are receiving barbiturate therapy.

Sodium thiopental in a mean induction dose of 6 mg/kg and a mean total dose of 8.5 ± 3 mg/kg has been used successfully as the sole anesthetic for CT and MRI in 200 children from 1 month to 12 years of age (Spear et al., 1993). Methohexital has a shorter recovery time than thiopental and is more effective than oral chloral hydrate (Manuli and Davies, 1993). Methohexital-induced seizures in patients with temporal lobe epilepsy have been reported. Thiopental or pentobarbital are alternatives for these patients (Rockoff and Goudsouzian, 1981). For patients taking barbiturate-containing anticonvulsant medications, a higher dose limit is generally more successful. Methohexital has also been used intramuscularly (IM) for radiotherapy in doses of 8 to 10 mg/kg. The onset time via this route is often twofold to threefold longer than rectally administered methohexital (Jeffries, 1988).

Although propofol does not have a labeled indication for children younger than 3 years of age, propofol has been used extensively in this age group as a means of providing sedation or anesthesia. Propofol sedation by bolus or continuous infusion for MRI scans of the brain can provide successful imaging conditions but with the risk of need for airway intervention and respiratory compromise (Vangerven et al., 1992; Cravero et al., 2009). Fatal metabolic acidosis and myocardial failure associated with lipemic serum have been reported in five children who were admitted to the ICU for respiratory support for upper respiratory tract infections while being sedated with continuous infusion propofol (Parke et al., 1992). Bloomfield and others (1993) have suggested a continuous infusion beginning at a rate of 99 mL/hr until the patients fall asleep (usually over 1 to 3 minutes) and then a decreasing rate during treatment, a strategy that works very well. Patients were typically awake, alert, and taking clear liquids 20 minutes later (Bloomfield et al., 1993).

Opiates reduce anesthetic, preprocedure, and postprocedure analgesic requirements. They are reversible with naloxone. Whereas narcotics may be unnecessary for diagnostic procedures that are not painful, they may be very useful for therapeutic interventions, especially for patients with postprocedural pain. They are also useful after anthracycline chemotherapy, with documented impaired myocardial function (Burrows et al., 1985). Because narcotics depress the ventilatory response to carbon dioxide (CO₂), this respiratory depression may be of particular concern for children with increased intracranial pressure. Narcotics may also worsen preexisting nausea and vomiting.

Benzodiazepines have the advantage of anxiolysis with minimal vomiting and cardiorespiratory depression. Diazepam is painful during IV injection and may lead to thrombophlebitis; midazolam is water soluble and therefore may be more suitable intravenously or intramuscularly. The elimination half-life of midazolam averages 2.5 hours, compared with 20 to 70 hours for diazepam (Greenblatt et al., 1981; Reves et al., 1985). Young patients or patients with significant liver disease may have prolonged duration and exaggerated effect of the benzodiazepines.

Preparation of the stomach and aspiration prophylaxis are of particular concern for urgently scheduled cases (outside of fasting guidelines) or when the medical history suggests aspiration risk. If using H₂-receptor antagonists, bronchospasm may occur in patients with asthma because of the relative increased availability of H₁-receptors. H₂-blockers may also inhibit metabolism of other concurrently administered medications. Metoclopramide accelerates gastric emptying and increases tone in the lower esophageal sphincter, but it is associated with a significant incidence of extrapyramidal side effects in children (Sledge et al., 1992). Ondansetron works synergistically with other agents through its vagal blocking actions in the gastrointestinal tract, as well as through its inhibition of the chemoreceptor trigger zone via serotonin receptor antagonism, particularly for patients undergoing radiation therapy with pulses of chemotherapy (Burnette and Perkins, 1992; Figg et al., 1993).

Ketamine has enjoyed great popularity during the past 30 years for sedation, analgesia, or anesthesia outside the operating room because of its support of the cardiovascular and respiratory systems. Ketamine-induced nightmares, hallucinations, delusions, and agitation are rare in children (Sussman, 1974; Hostetler and Davis, 2002). Karian and others (2002) have reported on a ketamine-sedation program for use in interventional radiology. In this program, IV or IM ketamine was administered in the interventional radiology suite by credentialed nurses and radiologists to patients undergoing select procedures. This protocol has allowed painful procedures to be tolerated by patients who previously would have required general anesthesia (Karian et al., 2002).

Dexmedetomidine, although not approved by the Food and Drug Administration (FDA) for pediatric use, obtained approval in October 2008 for adult procedural sedation in areas outside of the ICU. Particularly for pediatric sedation for radiologic imaging studies, dexmedetomidine alone in high dosages can achieve immobility for MRI and CT examinations (Mason et al., 2006, 2008a, 2008b). Its use for procedural sedation has still to be explored further, because its clinical application has been examined only in small studies and often in combination with ketamine (Barton et al., 2008).

Some patients require general anesthesia because of previous sedation failures, the need for a secure airway, or procedural logistics. Newer, less-soluble anesthetic agents such as sevoflurane and desflurane have pharmacokinetic profiles that compare favorably with propofol in adults; there seems little reason to think that this would not be the case with children, although pediatric anesthesiologists often avoid using desflurane because of its pungency and associated airway irritability (Van Hemelrijck et al., 1991). Since its introduction to clinical practice in the mid-1990s, sevoflurane has become the volatile anesthetic of choice in children. Its lack of airway irritability as a side effect and its ability to provide children with stable hemodynamic function, together with its rapid onset and offset make sevoflurane a useful agent for children (Furst et al., 1996).

Regional anesthesia, rarely administered outside the pediatric operating room, nevertheless remains a valid choice in some circumstances. Intercostal nerve blocks may be useful for lung or rib biopsies, chest tubes, biliary or subphrenic drainage procedures, and insertion of biliary stents. Nerve block of the brachial plexus by the axillary, interscalene, or supraclavicular route has been reported for the brachial approach to catheterization and neuraxial block of the lower extremities for femoral catheterizations and percutaneous approaches to the kidneys (Eggers et al., 1967; Ross, 1970; Lind and Mushlin, 1987). Spinal anesthesia in conjunction with regional hyperthermia and limb exsanguination has been successfully used for repeated painful radiotherapy on lower extremities (Spencer and Barnes, 1980).

Indwelling central catheters are implanted in the majority of radiotherapy patients and can be used for induction and maintenance of anesthesia, blood draws, IV fluid administration, and chemotherapy. Dressing changes are often accomplished in conjunction with the sedation or anesthesia. Antiseptic preparation of all injection sites with povidone-iodine and alcohol is critical. At the end of the session the catheter should be carefully flushed with heparinized saline. An alternative to central catheters is the use of a heparin-lock peripheral IV port, changed weekly, with careful parental instruction. Smoothness of emergence is particularly important after angiographic procedures because of the risk of a dislodged clot or bleeding at the puncture site. Some patients have been heparinized without protamine reversal. Unlike adults, sand bags and weights are not routinely applied to angiographic cannulation sites of children.

Occasionally, the loss of self-control with sedation results in dysphoria, and some patients fare better when they are completely awake. Minimal medication may be preferable in patients with complicated and unstable medical conditions who may not tolerate the anesthesia or sedation. Some procedures (e.g., unilateral carotid barbiturate injection or the Wada test) may require conversation, interaction, and responsiveness of the patient. In these situations, no sedation may be the best alternative.

Postanesthesia care

Recovery criteria and the postanesthesia care unit (PACU) environment in an extramural location must be no different than the postanesthesia care delivered to children after an operative procedure. Each site must have sources of supplemental oxygen, the ability to deliver positive pressure ventilation, the availability of suction and monitoring equipment, and a nursing staff trained in postanesthesia care. Discharge criteria should be established by an anesthesiologist in conjunction with the extramural service and its nursing staff.

Postprocedure analgesic requirements are extremely variable. Whereas a groin puncture may be only mildly annoying for adults, the inability to move about and the ache of blood dissecting subcutaneously causes considerable discomfort in children. All children who have undergone angiography require a minimum PACU stay of 4 hours to ensure that the puncture site does not bleed or develop a hematoma. Ideally, a patient should be free of pain and resting supine and motionless in order to minimize the risk of a groin-puncture bleed or hematoma. An experienced member of the nursing staff should be able to recognize and manage unexpected agitation, delirium, or an unanticipated or undesired change in mental status and know to call for extra help.

The anesthesiologist may be asked to participate in the perioperative care of patients who have had embolization procedures. These patients often experience pain or swelling after the procedure, with the severity of discomfort depending on the extent of embolization, the agent used for embolization, postembolic swelling, and the amount of tissue necrosis. A variety of analgesic techniques are available, and the use of steroids perioperatively, although they do not directly decrease pain, may be of benefit in reducing edema and postembolic neuritis. Postembolic swelling influences perioperative airway management for procedures in the head and neck. Pediatric patients may need to remain intubated after such procedures, particularly when visible edema in the floor of the mouth, tongue, hypopharynx, oropharynx, or anterior neck could compromise the airway.

Nausea or vomiting may increase venous blood pressure because of the Valsalva maneuver, which can aggravate bleeding and swelling in puncture sites or after head and neck procedures. Hypothermia is a risk at some extramural locations because the MRI, CT, and interventional radiology equipment require a cool environment. Heating lamps and forced air heaters may be used when it is safe and appropriate to do so. Finally, with the use of iodine-containing radiocontrast media, as well as sclerosing and embolizing agents, consideration must be given to adequate volume resuscitation, the risk of a contrast reaction, and bladder catheterization for detection of oliguria, polyuria, or hematuria.

Resuscitation

Each extramural anesthetizing location is unique with regard to conducting resuscitation. Redundancy of monitoring devices and equipment is important; a provider should not be limited to a single item that could malfunction at the time of resuscitation. Patients with multiple allergies, shellfish allergies, or atopic disease are at increased risk of exhibiting anaphylaxis to iodine-containing contrast. These patients may benefit from pretreatment with steroids and antihistamines. Areas with restricted access (MRI in particular) should have designated adjacent locations to perform full resuscitation. These areas should be equipped with wall oxygen, suction, and full monitoring and resuscitation capability. A self-inflating silicone bag (no ferromagnetic working parts) or nonferrous Jackson-Rees circuit should always be kept inside the MRI suite.

The physicians, nurses, anesthesiologists, technologists, and support personnel must know the location of a readily accessible code cart. In addition, a hard board to be placed under the patient during resuscitation should be available. Mock codes should be performed regularly to ensure adequate flow, teamwork, and delineation of responsibilities in the event of an emergency. The MRI scanner poses a special problem. Codes should never be conducted in the scanner because as support personnel rush inside to assist, ferrous materials that are not removed will become projectile and create an even more hazardous situation. Quenching a magnet should not be an alternative, because it requires a minimum of 3 minutes to eliminate the magnetic field. In addition, inadequate exhaust during a quench has been known to produce hypoxic conditions in the scanner and has resulted in patient death. A “black quench” could melt the MRI coils and require replacement of the scanner, a costly and time-consuming undertaking. Defibrillators are not compatible with MRI and may not function properly when they are exposed to the magnetic field (Snowdon, 1989). In an emergency, a patient should be removed from the scanner to an area outside of the magnetic field. This designated area is a safe place for resuscitation and should have not only a wall oxygen source for a self-inflating bag but also access to appropriate monitors.

Specific extramural sites

Radiology

Computerized Tomography Scan

CT differentiates between high-density (e.g., calcium, iron, bone, and contrast-enhanced vascular and cerebrospinal fluid [CSF] spaces) and low-density (e.g., oxygen, nitrogen, carbon in air, fat, CSF, muscle, white matter, gray matter, and water-containing lesions) structures. Because the scan time is quick, CT may be preferable for patients who are medically unstable and in need of rapid diagnosis—for example, with the child being evaluated for abuse, an intracranial hemorrhage, or abdominal or thoracic mass. Other indications for emergency CT scans may include encephalopathy and a change in neurologic status. In these situations, the issues of a full stomach and increased intracranial pressure usually necessitate a rapid-sequence induction with tracheal intubation. A CT scan of the head is often the preferred study in emergency situations where head trauma is involved (Blankenberg et al., 2000).

The actual scanning sequences are short and can range from 10 to 40 seconds. These short scan times enable many children to complete a CT scan without any sedation, especially with parental presence and distraction techniques. When an anesthesiologist is involved, it is often for airway or failed-sedation issues or for a medically complicated patient. An important aspect of some CT scans is to visualize the sinuses, ears, inner auditory canal, and temporomandibular bones and to evaluate for choanal atresia or craniofacial abnormalities. These scans may require direct coronal imaging with extreme head extension (off the end of the table at an angle between 40 and 70 degrees) or absolute immobility for three-dimensional reconstruction, so it is critical for the treatment team to have a thorough understanding of the specifics of the study. Three-dimensional airway and cardiac studies have evolved and have unique anesthetic requirements. The airway studies require breath holding on inspiration and expiration in order to allow visualization of areas with airway collapse (Lee et al., 2008). The cardiac studies are often done in collaboration with cardiologists and radiologists who are able to make structural and functional assessments of the heart. These scans can also be challenging, because adenosine is often requested in order to briefly pause heart function so that image quality is maximized (Woodard et al., 2006).

Any patient who is at risk for cervical instability should be properly screened before neck extension. Children with Down syndrome are at risk for atlantoaxial instability. The incidence of instability varies from 12% to 32% (Blankenberg et al., 2000). Many children with Down syndrome require cervical spine radiographs before entering grade school or participating in Special Olympics. Usually, the parents are well aware of the radiologic findings. The cervical spine films, however, do not indicate whether or not a child is at risk for dislocation (Davidson, 1988). Rather, those children who exhibit neurologic signs or symptoms such as abnormal gait, increased clumsiness, fatigue with ambulation, or a new preference for sitting games are at risk. In infants, developmental milestones (e.g., crawling, sitting up, and reaching for objects) should be verified. Physical signs of Down syndrome may include clonus, hyperreflexia, quadriparesis, neurogenic bladder, hemiparesis, ataxia, and sensory loss. The asymptomatic Down syndrome child with radiologic evidence of instability may be approved for procedural sedation; however, unnecessary neck movement should be avoided. Any child who displays neurologic signs or symptoms should not be sedated until a neurosurgical or orthopedic consultation is obtained.

Radiologists employ Gastrografin when evaluating abdominal masses. Gastrografin diluted to a concentration of 1.5% is usually considered a clear liquid. The volume that is administered orally is significant; newborns younger than 1 month of age receive 60 to 90 mL, infants between 1 month and 1 year of age may receive up to 240 mL, and children between the ages of 1 and 5 years receive between 240 and 360 mL. Because sedation or anesthesia should usually be accomplished within a window of 1 to 2 hours after ingestion of the contrast, most “elective” fasting guidelines would be violated; however, the scan must be completed while the Gastrografin is still in the gastrointestinal tract. There are no published data to guide optimal induction or sedation techniques as they relate to aspiration risk in these circumstances. Full strength (3%) Gastrografin is hyperosmolar and hypertonic. All Gastrografin should be diluted to an isosmolar and isotonic 1.5% concentration of neutral pH. There is one case report of 1.5% Gastrografin aspiration in a child with no adverse sequelae; therefore, the risk of using a 1.5% concentration of Gastrografin seems low (Friedman et al., 1986; Wells et al., 1991).

Embolization Procedures

Interventional techniques include nonvascular and vascular interventions (Towbin and Ball, 1988). In vascular interventions, embolization and sclerotherapy have become important techniques for treating vascular malformations, aneurysms, fistulas, and hemorrhage; for accomplishing renal ablation; and for presurgical embolization of hypervascular masses. Percutaneous transluminal angioplasty and fibrinolytic therapy are increasing in pediatric institutions; great success is being reported, even in the smallest infants, and the important contribution that adequate sedation and analgesia can make to ultimate outcome has been recognized (Diament et al., 1985).

Vascular malformations are congenital aberrant connections between blood vessels and may be composed of lymphatic, arterial, and venous connections. These lesions, although present at birth, are often discrete and not clearly visible. As the child grows, the vascular malformation may expand rapidly, growing with the child. This rapid proliferative phase may occur in response to hormonal changes (e.g., pregnancy or puberty), trauma, or other stimuli (Jackson et al., 1993). Vascular malformations may be high-flow or low-flow lesions, depending on which vessels are involved. High-flow lesions include arteriovenous fistulas, some large hemangiomas, and arteriovenous malformations. Particularly with large lesions, high-output cardiac failure and congestive heart failure with the potential for pulmonary edema should be anticipated and sought out in the medical history and physical examination. Low-flow lesions consist of venous, intramuscular venous, and lymphatic malformations. Surgical resection of symptomatic vascular malformations may be hazardous as well as unsuccessful—any vascular element not resected may enlarge and cause further problems.

Because vascular malformations enlarge over time, even asymptomatic lesions may require intervention. Patients with symptoms may suffer from pain, tissue ulceration, disfigurement, airway or cardiovascular compromise, impairment of limb function, coagulopathy, claudication, hemorrhage, and progressive nerve degeneration or palsy. Because large vascular lesions require multiple embolizations, parents and patients are often comforted by seeing familiar anesthesiologists, another benefit of having a core group of anesthesiologists in the radiology suite. Vascular embolization is also used as a bridge to surgical resection. Successful embolization and sclerotherapy decrease the size of the malformation and reduce blood flow to the lesion, thereby decreasing surgical risks.

When embolizing vascular malformations, radiologists often aim to cut off not only the feeding vessels but also the central confluence (nidus) where much of the arterial shunting occurs. Embolic agents include stainless-steel minicoils, absorbable gelatin pledgets and powder, detachable silicone balloons, polyvinyl alcohol foam, cyanoacrylate glue, and ethanol. The choice of agent depends on the clinical situation and the size of the blood vessel. When permanent occlusion is the goal, polyvinyl alcohol foam and ethanol are often employed. Both occlude at the level of the arterioles and capillaries. Medium to small-sized arteries may be occluded with coils, the equivalent of surgical ligation. Particularly in trauma situations, when only temporary occlusion (days) is the goal, absorbable gelatin pledgets or powder are used (Coldwell et al., 1994).

Large hemangiomas may be associated with the coagulopathy of Kasabach-Merritt syndrome. In this condition, the hemangioma traps and destroys platelets and other coagulation factors, resulting in thrombocytopenia and an increased risk of bleeding. As the hemangioma involutes, the coagulation status improves (Mulliken and Young, 1988). A condition described as systemic intravascular coagulation (SIC) can occur after the embolization of extensive vascular malformations. This condition is marked by an elevated prothrombin time (PT) with a decrease in coagulation factors and platelets.

Absolute (99.9%) ethanol is injected in vascular malformations to promote sclerosis. Ethanol may produce a coagulum of blood and cause endothelial necrosis (Becker et al., 1984). Sclerotherapy or embolization with absolute ethanol increases the risk of developing a postprocedure coagulopathy marked by positive D-dimers, elevated PT, and decreased platelets (Mason et al., 2001b). Ethanol causes thrombosis, because it injures the vascular endothelium. Ethanol also denatures blood proteins. Extensive ethanol injections can cause hematuria, and urinary catheters should be inserted to monitor urine output, diuresis, and hematuria. Especially with children scheduled for outpatient surgery, liberal fluid replacement ensures that the hematuria clears before discharge. Ethanol can cause neuropathy and tissue necrosis if it is not injected selectively. Using selective catheterization and direct percutaneous puncture, care is taken not to expose normal blood vessels to the ethanol. In addition to the risk of hematuria, ethanol also can produce significant serum alcohol levels. Mason and others (2000) note that up to 1 mL/kg of ethanol can be administered and that serum ethanol levels have been greater than the intoxication level of .008 mg/dL (Fig. 33-1). Patients with high serum-ethanol levels may be either sedated or extremely agitated, depending on their particular response to intoxication.

FIGURE 33-1 Relationship between ethanol administered (mL/kg) and serum ethanol level (mg/dL).

Embolization or balloon occlusion of arterial venous malformations, vascular tumors, intracranial aneurysms, and fistulae carries considerable risk of catastrophic results. Risks include a sudden intracranial hemorrhage, acute cerebral ischemia, or catheter or balloon migration. If sedated, the patient may require urgent airway management. Long cases require a urinary catheter, especially if contrast material is used.

Cerebral angiography requires motionlessness as well as exquisite control of ventilation. Anesthetic technique, in choice of agent as well as in control of arterial CO₂ tension, may affect cerebral blood flow and hence the quality of the scan. Cerebral angiography may be performed in children for the diagnosis or follow-up study of Moyamoya disease, and these children should have anesthetic techniques that minimize the risk of transient ischemic attacks (TIAs) and stroke during the procedure (Soriano et al., 1993). Other considerations include controlled hypercarbia to promote vasodilation and facilitate access and visualization of the vasculature for the radiologist. In the event of vasospasm or difficult access of small, torturous vessels, locally administered (through the catheter) nitroglycerin in small doses (25 to 50 mcg) may facilitate visualization and access. Occlusion of the venous portion of the arteriovenous malformation (AVM) without complete occlusion of the arterial inflow vessels could result in acute swelling and bleeding. Vascularity reduction through occlusion of major feeder vessels is the goal of embolizing large AVMs before planned surgical excision. This may be accomplished as a staged procedure over several days, involving repeated anesthetics or sedation sessions.

Angiographic imaging may be enhanced through the use of glucagon. Glucagon is efficacious for digital subtraction angiography, visceral angiography, and selective arterial injection in the viscera. When needed, glucagon is administered intravenously in divided doses of 0.25 mg to a maximum of 1 mg. Risks include glucagon-induced hyperglycemia, vomiting (particularly when given rapidly), gastric hypotonia, and provocation signs of pheochromocytoma (McLoughlin et al., 1981; Chernish et al., 1990; Jehenson, 1991). Children who receive glucagon should routinely receive prophylactic antiemetics.

The ability to intermittently assess neurologic function and mental status is invaluable during embolization procedures, but it may not be practical in children because of fear, pain, and movement. General anesthesia permits easier control of blood pressure and ventilation and eliminates the concern about patient movement. For children, general anesthesia is often preferred when performing high-risk procedures that require immobility and periods of breath-holding. Preprocedural assessment should include any history of seizures, bleeding, treatment with anticonvulsants or anticoagulants, neurologic symptoms, and evaluation of intracranial-pressure status. It is important to determine whether the patient has had any TIAs or has evidence of cerebrovascular occlusion. Vasodilator agents (calcium channel blockers) or nitrate derivatives may need to be administered after embolization. Because many patients are anticoagulated during the procedure, a preoperative coagulation profile should be obtained. A variety of anticoagulants may have to be on hand as well to prophylaxis for thrombosis (Bidabe et al., 1990).

Morbidity associated with embolization is not negligible. Arteriovenous malformations (AVMs) involving the head and neck often require cannulation of the external carotid artery branches and the thyrocervical trunk. All patients scheduled for embolization should be typed and cross-matched for blood. Those patients who undergo embolizations of AVMs of the head and neck are at risk for stroke, cranial nerve palsies, skin necrosis, blindness, infection, and pulmonary embolism (Riles et al., 1993). It is important to assess and document full return of neurologic status after the patient is extubated.