Anesthesia and Sedation for Pediatric Procedures Outside the Operating Room

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CHAPTER 33 Anesthesia and Sedation for Pediatric Procedures Outside the Operating Room

Keira P. Mason and Robert S. Holzman

Contents

Requirements for Extramural Locations

• Organization and Administration
• Personnel, Support, and Logistics
Periprocedural Patient Care: Standards of Practice and Quality Assurance

• Scheduling and Preparation of Patients
• Selection of Agents and Techniques
Postanesthesia Care
Resuscitation
Specific Extramural Sites

• Radiology
• Nuclear Medicine
• Radiation Oncology
• Clinic and Office Procedures
Safety Issues for Patients and Their Anesthesiologists

• Use of Intravascular Contrast Media
• Ionizing Radiation
• High-Intensity Magnetic Fields
Difficult-Airway Management in the Radiology Suite
Blood-Loss Management Outside of the Operating Room
Summary

Advances in imaging and endoscopic technology requests from medical colleagues for support during prolonged or high-risk procedures and concern about liability exposure have led to increasing demands for anesthesiologists’ professional services outside the operating room. In the 14 years since the first publication of this chapter, anesthesia services outside the operating room have increased more than sixfold at Children’s Hospital Boston to over 7000 anesthetic procedures annually. As the demand for sedation services has increased nationally, so also have nonanesthesiologists expressed an interest in providing these services and are often using anesthesia billing codes. Indeed, pediatric radiologists, oncologists, dentists, gastroenterologists, pulmonologists, pediatricians, hospitalists, and intensivists are all able to supervise and deliver sedation. Monitoring techniques, sedative choices, and sedation guidelines vary between specialty organizations. Although the American Academy of Pediatrics (AAP) recently updated its guidelines, the recommendations of the American College of Gastroenterology and the American College of Emergency Physicians differ from those of the AAP (AAP et al., 2008).

Anesthesia departments may be reluctant or unable to commit limited financial resources to providing state-of-the-art anesthesia equipment and monitors to extramural locations with limited caseloads. Historically, anesthesia equipment and monitors designed for the outfield environment—small, portable, or safe for use with magnetic resonance imaging (MRI)—are at least double the costs of their operating-room counterparts. In addition, insurance reimbursement may be difficult, because insurers do not always understand the need for an anesthesiologist. Nonsurgical colleagues and support personnel may have little experience with anesthesia care, delivery, and needs, particularly in urgent situations. Even anesthesiologists are challenged, as few are familiar with the specific requirements associated with interventional, endoscopic, or radiologic procedures. Conflicts may inevitably arise between physicians, administrative personnel, and insurers, particularly because each group has different priorities and expectations. This chapter explores the requirements for anesthetic administration outside the operating room, the available anesthetic techniques, and some specialty-specific considerations. It concludes with current and important safety issues.

Requirements for extramural locations

Organization and Administration

A collaborative relationship between extramural and anesthesiology departments is critical to providing safe patient care. At a minimum, safe patient care requires appropriate anesthesia equipment and monitors, adequate space, and experienced ancillary providers who are knowledgeable in anesthesia and facile in providing assistance if needed. Each off-site area has its own needs, goals, and guidelines. It is ideal to designate a team of anesthesiologists committed to providing extramural anesthesia care and troubleshooting the logistical challenges in the various locations. Each member should rotate regularly through the different extramural sites in order to maintain familiarity with the procedures, to foster a relationship with the physicians and ancillary personnel, to understand the anesthesia demands unique to each site, and sharing information about ongoing advances. Technological advances are particularly expanding in the field of radiology, and complicated imaging studies challenge the anesthesiologist to have an understanding of the unique conditions that each study requires. Understanding these requirements will guide the anesthesiologist in developing a management plan (Lee et al, 2008).

In the past, extramural locations were not designed with the anesthesiologist in mind. The need for anesthesia had not been anticipated when off-site locations were planned. It is only within the past decade that the demand for anesthesia services in these sites has burgeoned. Thus, most off-site locations have not been configured to support the capabilities for anesthesia. Ideally, anesthesiologists should be involved in the early stages of site design to ensure that minimum standards for anesthesia delivery are met and to troubleshoot engineering issues and advocate for adequate space for anesthetic induction and emergence (Committee on Drugs, 1992; American Academy of Pediatrics Section on Anesthesiology, 1999). Physical plant considerations for MRI-site planning have been previously described (Koskinen, 1985). When anesthesia services are requested, these sites may not meet minimum standards and may require reengineering to meet minimum requirements of the American Society of Anesthesiologists (ASA) (House et al., 1994). The anesthesia machine should be equipped with back-up supplies of E cylinders filled with oxygen and nitrous oxide. If pipeline oxygen is not available, then oxygen should be supplied from H cylinders (6600 L) rather than the smaller E tanks (659 L).

Scavenging systems should be carefully evaluated in the extramural location. Unlike the operating room, passive scavenging systems may not always be possible. A safe means of active scavenging may be provided by the vacuum at the wall or wall suction canisters. A scavenging system should be dedicated solely to waste gases. Many MRI scanners do not have wall suction because MRI-compatible wall suction is not widely available. If the suction is located outside the MRI suite, then a mouse-sized hole may be created in the suite’s wall to allow suction tubing to be passed inside (Koskinen, 1985).

Electrical circuitry and lighting in extramural locations may not be up to operating room standards, even if the outlets are grounded and up to hospital grade. Although some extramural locations carry minimal risk of electrical shock or electrocution, these sites do not have line-isolation monitors (LIMs) and therefore do not warn of excess leakage of current. Supplemental lighting for recordkeeping, label verification, establishment of intravenous (IV) access, and visualization of the patient is critical. Even under the best circumstances, for example, lighting is dim in the MRI scanner, and monitoring by simple clinical observation can be limited. Anesthesia personnel may not always remain in the imaging suite, particularly during ionizing radiation imaging, computerized tomography (CT) scanning, and radiation therapy. Monitoring capabilities via remote television or hardwiring through reinforced walls can allow video display of the patient and the physiologic monitors within.

A storage area large enough to stock anesthesia equipment and supplies must be easily and quickly accessible. This area should be routinely checked, restocked, and kept locked when anesthesia services are not required. The need for redundancy of nondisposable supplies is a matter of philosophy. Are two laryngoscopes enough, or should there be a third? Is one electrocardiograph (ECG) monitor enough, or should there be a battery-operated monitor for back-up and transport? Drugs should be checked according to the usual operating-room routine, and expired medications should be replaced. Gas-cylinder supplies must be reliable, especially in areas without piped oxygen. A code cart should be conveniently located in an area known to all physicians and ancillary personnel. This cart should be routinely checked and restocked. With larger volumes of patients necessitating significantly sized critical care areas, strong consideration should be given to having a difficult-airway cart available at extramural locations.

Finally, extramural anesthetizing locations are often distant from the operating room. Patients may need to remain anesthetized during transport to or from the extramural location. For these circumstances, assured elevator access with key-controlled emergency overrides is a must. All anesthesiologists who deliver extramural services should be familiar with their surroundings. Checklists are invaluable to guarantee consistent patient care, anesthesia monitoring, equipment, documentation, and back-up assistance.

Personnel, Support, and Logistics

Support and medical personnel in nonsurgical areas may not be familiar with the requirements of an anesthesiologist, thus providing an important educational and training opportunity. Proper training facilitates teamwork and minimizes chaos in critical situations. A standard anesthesia cart at each anesthetizing location should be fully stocked with essential medications, necessary additional equipment, a spare self-inflating bag, endotracheal tubes, laryngeal mask airways (LMAs), suction catheters, IV supplies, laryngoscope handles and blades, and a variety of oral and nasopharyngeal airways.

Leadership is crucial; a director of anesthesia services at an extramural location can orchestrate, facilitate, and coordinate anesthesia services. This director can also serve as a consultant for the other medical and nursing staff. By being available to answer questions, do on-site consultations, examine patients, and provide back-up support or emergency-airway expertise, the anesthesiologist can also support a nurse-administered sedation program. Nurses who provide sedation under the supervision of the ordering extramural physician (e.g., gastrointestinal, radiologic, or dental) should have Pediatric Advanced Life Support (PALS) and Basic Life Support (BLS) certifications. The Joint Commission on Accreditation of Healthcare Organizations (JCAHO) (2009) requires that individuals who administer sedation are able to rescue patients from whatever level of sedation or anesthesia is achieved, whether intentional or unintentional. All children scheduled for nursing sedation during a scan should receive a prescreening telephone call from a radiology nurse the day before the scheduled scan. Often, these telephone calls are made after business hours to ensure that a parent is home. The nurse reviews the medical history, relays fasting instructions, and reminds the parent to administer the child’s routine medications with a sip of clear fluid. The supervising physician must give final approval for sedation after reviewing the child’s medical history and current medical status and before ordering the medications. To minimize the chance of drug-delivery error or miscalculation, it is helpful to have preprinted order sheets or a computerized order-entry template.

It is crucial to know whom to call for assistance if a problem arises. A speed-dial system should be available from all extramural anesthetizing location sites in order to immediately request emergency back-up help.

Periprocedural patient care: standards of practice and quality assurance

The practice standards adopted by the American Society of Anesthesiologists (ASA) in 1986 for basic intraoperative monitoring apply to extramural locations as well. Practice standards and guidelines promulgated by the AAP are exceeded by established practice standards in anesthesiology (Committee on Drugs, 1992; Anesthesiology and Pediatrics, 1999). Significant variances may exist when practitioners who are not anesthesiologists administer sedation (Keeter et al., 1990). Practice Standards for Non-Anesthetizing Locations were adopted by the ASA in 1994 (ASA House of Delegates, 1994).

As recommended by the JCAHO, sedation-related policies and procedures should be part of a quality-assurance initiative that should accompany all sedation programs. Ideally, adverse events such as failed or prolonged sedations, paradoxical reactions, hypoxia, emesis, unscheduled admissions, or cardiac and respiratory events should be identified and entered into a computerized database. In addition, the extramural nurse should call all patients and families within 24 hours in order to follow-up care on patient outcome and identify any delayed adverse events.

Scheduling and Preparation of Patients

Appropriate planning for an anesthetic begins with a familiarity with the procedure. The requesting service orders the procedure and then leaves the logistics of scheduling to the extramural service. Radiologists recognize that involvement with anesthesia lengthens their total time commitment to a patient and potentially limits the number of procedures accomplished in a day (Winter, 1978; Cremin, 1990). A well-coordinated system to screen patients on the day of the procedure is important. Experienced personnel, ideally a certified pediatric nurse practitioner (CPNP), should be designated to take initial vital signs, review recent medical history, begin IV lines if necessary, and familiarize the family with the upcoming procedure, including anesthesia.

Screening patients for extramural procedures may be challenging and time consuming. Many children are chronically ill, nutritionally impaired, and have complicated medical conditions. These issues must be carefully addressed through attention to the patient’s history, physical examination, old medical records, outside consultations, and close communication with other medical colleagues. Several consultants may need to confer in order to fully understand the patient’s current state of health. Not every procedure is elective. Urgent procedures may be required despite an upper respiratory tract infection (URI), ongoing pneumonia, deteriorating physical status, untreated gastroesophageal reflux, sepsis, or hemodynamic instability. In these situations, consultation between the anesthesiologist, the requesting physician, and the radiologist should confirm urgency. Anesthesia plans should be adjusted to accommodate the requirements of the procedure (e.g., holding breath for a CT scan of the chest) and the patient’s medical condition.

It is not always possible for an anesthesiologist to provide sedation and anesthesia for all children when there is a large volume of cases. A structured nursing sedation program can provide safe and effective sedation. In many hospitals, the extramural department (gastroenterology, radiology, cardiology) outsources responsibility for sedation to another department, which could include pediatrics, hospital medicine, anesthesiology, intensive care, or emergency medicine. After screening the patient, an appropriate referral for either general anesthesia or procedural sedation is the usual result. Because MRI is a unique environment, it is more efficient to have the MRI nurses screen patients before and on the day of the procedure. To ensure consistent decision making, the anesthesiology and radiology departments should develop a set of guidelines and easily identifiable “red flags ”to help in this triaging process (Table 33-1). If any questions arise, additional medical history needs to be clarified, or additional studies need to be performed, the nurse and anesthesiologist confer before making the final decision regarding general anesthesia or procedural sedation. In addition, chronically ill children often have electrolyte disturbances, coagulation and hematologic abnormalities, and hemodynamic instability. A consent for the administration of general anesthesia or procedural sedation must be obtained in parity with policies established for anesthesia in the operating room.

TABLE 33-1 Red Flags for Sedation

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.

image

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.

Ultrasound-Directed Procedures

Needle biopsies and drainage procedures are directed with ultrasound guidance for diagnostic examination (e.g., of the kidneys, liver, lungs, muscle, unknown mass, or unknown fluid). Percutaneous drainage of abscesses, cysts, pancreatic pseudocysts, and other fluid-containing structures can often be accomplished with ultrasound guidance. Ultrasound is useful for placement of difficult central venous-line (CVL) catheters and peripherally inserted central catheters (PICCs). The requirement for general anesthesia vs. sedation for ultrasound-guided procedures depends in part on the duration of the procedure, the location involved, the risks associated with the procedure, and any procedural requirements. The need for controlled ventilation with breath holding may require an endotracheal tube and general anesthesia. Associated secondary effects of the end-organ disease must be kept in mind in the overall anesthetic care plan.

Magnetic Resonance Imaging

Atoms with an odd number of protons or neutrons are capable of acting as magnets. When they are aligned in a static magnetic field, they can be subjected to radiofrequent energy that alters their original orientation. With removal of the radiofrequency pulse, the nuclei rotate back to their original alignment (relaxation), and the energy released can be detected and transformed into an image. Hydrogen is the atom most often used for imaging, because it is present in most tissues as water and long-chain triglycerides.

MRI is employed for the evaluation of neoplasms, trauma, skeletal abnormalities, and vascular anatomy (Barnes, 1992). MRIs of the brain are often performed to evaluate developmental delay, behavioral disorders, seizures, failure to thrive, apnea and cyanosis, hypotonia, and mitochondrial or metabolic disorders. Magnetic resonance angiography and venography (MRA and MRV) are especially helpful in evaluating vascular flow and can sometimes replace invasive catheterization studies for follow-up or initial evaluations of vascular malformations, interventional treatment, or radiotherapy (Edelman and Warach, 1993). Functional MRI (fMRI) is an evolving technology that measures the hemodynamic or even metabolic response related to neural activity in the brain or spinal cord. fMRI is often able to localize sites of brain activation and is now dominating brain-mapping techniques because of its low invasiveness and lack of radiation exposure. Some fMRI studies require cognitive facility and are typically interactive with a conscious and responsive patient. fMRI studies on children who are unable to respond appropriately either because of age or cognitive compromise are challenging—how that will evolve in pediatric anesthesiology practice is not yet clear.

Historically, the anesthetic management of children in the MRI suite has been highly dependent and somewhat limited by MRI-compatible monitors and anesthesia gas machines. (Karlik et al., 1988; Menon et al., 1992; Tobin et al., 1992). The American College of Radiology (ACR) established guidelines to minimize the risk of MRI-related mishaps but did not address the needs of the anesthesiologist (Kanal et al., 2007). These guidelines were written in response to fatalities that had occurred when loose, nonferrous oxygen cylinders became projectiles when brought inadvertently into the MRI suite with a patient in the bore of the magnet (Chaljub et al., 2001). In 2008 the ASA assembled a task force composed of anesthesiologists and a radiologist with MRI expertise. This Task Force on Anesthetic Care for Magnetic Resonance Imaging created a document entitled the Practice Advisory on Anesthetic Care for Magnetic Resonance Imaging (ASA Task Force on Anesthetic Care for MRI, 2009). This document establishes important recommendations for safe practice as well as consistency of anesthesia care in the MRI environment. Most important, the Practice Advisory includes all sedation, including monitored anesthesia care, general anesthesia, critical care, and ventilatory support. Conditions of high-risk imaging were defined as imaging in patients with medical or health-related risks or as equipment-related, procedure-related, or surgery-related risks. MRI-guided interventions, cardiac imaging, and airway imaging were all identified as high-risk procedures. The Task Force was designed to promote patient and health care provider safety, prevent MRI mishaps, recognize limitations in physiologic monitoring, optimize patient management, and identify potential equipment and health risks (ASA Task Force on Anesthetic Care for MRI, 2009).

Anesthetic management also depends on the availability of support personnel, equipment and monitors; the personal style and comfort level of the anesthesiologist; and the patient’s particular medical history. Requiring a general anesthetic solely to ensure motionless conditions for a radiologic imaging study is often a frightening concept for parents. Parents often equate pain and surgical interventions with the need for anesthesia and are reluctant to expose their child to a general anesthetic for the sake of an MRI study. Children under the age of 5 years most commonly require moderate or deep sedation or an anesthetic to ensure motionless conditions. Ketamine, narcotics, or benzodiazepines are generally unsuccessful. Pentobarbital, propofol, and dexmedetomidine offer successful alternatives to inhalation anesthesia (Mason et al., 2001a, 2004, 2008a, 2008b; Guenther et al., 2003, Yamamoto, 2008). One technique for general anesthesia is to perform an inhalation induction followed by placement of an LMA. During the scan, the patient maintains spontaneous ventilation. Lidocaine gel (2%) on the LMA cuff is a useful adjunct, because it decreases the incidence of sore throat and retching (Chan and Tham, 1995; Keller et al., 1997). A retrospective study of 200 patients demonstrated the usefulness of this approach (Brimacombe et al., 1995). In children with upper respiratory infections, there was a lower incidence of mild bronchospasm, laryngospasm, breath-holding, and major oxygen desaturation (less than 90%) in the group with LMAs compared with the group that received endotracheal anesthesia (Tait et al., 1998). Temperature monitoring can be accomplished by liquid crystal display (skin temperature). There is still no means of monitoring core temperature, because any temperature probe would risk heat generation and thermal burns to the patient.

Anesthesiologists must be aware of many personal items taken for granted—clipboards, pens, watches, scissors, clamps, credit cards, eyeglasses, and paper clips that should not be in the MRI field (Karlik et al., 1988; Menon et al., 1992; Tobin et al., 1992). Conventional ECG monitoring is not possible, because as the lead wires traverse the magnetic fields, image degradation occurs and, most importantly, the ECG leads heat and cause burns on the patient. Fiberoptic ECG monitoring is necessary to minimize the risk of patient burn. Even with fiberoptic cables, it is important to recognize that the connections between the ECG pads and the telemetry box are still hardwired, and careful attention must be paid to prevent frays, overlap, exposed wires, and knots in the cables (Shellock, 1989). In order to prevent injury to the patient, care must be used to avoid creating a conductive loop between the patient and a conductor (e.g., ECG monitoring and gating leads, plethysmographic gating wire, and fingertip attachments). During the scan, no exposed wires or conductors can touch the patient’s skin, and no imaging coil can be left unconnected to the magnet. Pulse oximeters are also not conventional to the operating room environment; rather they are fiberoptic. Failure to remove the conventional pulse oximeter probes and adhesives has resulted in second- and third-degree burns (Shellock, 1989; Brow et al., 1993).

Current advances in physiologic monitoring and anesthesia machines for the MRI environment have optimized the ability of the anesthesia care provider to provide safe care in the MRI suite. The Dräger Fabius MRI (Dräger Medical AG; Lübeck, Germany) was designed for MRI and approved by the FDA in 2008 for use within both a 1.5-Tesla (T) and 3-T magnetic field up to a field strength of 400 gauss. The Dräger Fabius MRI, equipped with two vaporizers, is an electronically controlled ventilator and the first one able to deliver multiple modes of ventilation in the MRI suite. Advances in physiologic monitoring now offer the ability to monitor ECG and pulse oximetry in a 1.5-T and 3-T MRI scanner via wireless, fiberoptic communication (Invivo Precess, Inviv; Orlando, Florida).

Average noise levels of 95 dB have been measured in a 1.5-T MRI scanner; this level of noise is comparable with the noise level of very heavy traffic (92 dB) or light road work (90 to 110 dB). Exposure to this level of noise has not been considered hazardous if it is limited to less than 2 hours per day (Gangarosa et al., 1987). There are case reports, however, of both temporary and permanent hearing loss after an MRI scan (Brummett et al., 1988; Kanal et al., 1990). Three-Tesla magnets offer the advantage of less image degradation and improved neuroskeletal and musculoskeletal imaging. As the field strength increases, so does the noise (Hattori et al., 2007). In fact, the peak sound-pressure level of a 3-T magnet exceeds 99 dB, the level approved by the International Electrotechnical Commission. Noise reduction did not differ between earplugs and headphones, although the combination of both was more effective at reducing sound (Hattori et al., 2007). Earplugs or MRI-compatible headphones should be offered to all pediatric patients and are required for all patients imaged in the 3-T MRI scanner. fMRI provides additional challenges in the 3-T environment; the noise of the 3 T can interfere with the acoustic stimulation generated for purposes of obtaining the fMRI (Ravicz et al., 2000; Menendez-Colino et al., 2007). Video goggles compatible with the 1.5-T and 3-T environments (Resonance Technology; Los Angeles, California) may be worn by the patient during MR imaging to provide a three-dimensional virtual reality system complete with audio integration. The introduction of this integrated audio-video headset has revolutionized the ability to offer distraction to patients, many of whom are able to tolerate imaging without adjuvant sedation or anesthesia.

Although studies in mice and dogs suggest that exposure to magnetic fields may increase body temperature, it is unlikely that static magnetic fields up to 1.5 T have any effect on core body temperature in adult humans (Sperber et al., 1984; Shellock et al., 1986; Shuman et al., 1988). However, this may be of greater concern in infants and small children, especially in cases like cardiac MRI studies that require a long scan time. The specific absorption rate (SAR) is measured in watts per kilogram and is used to follow the effects of radiofrequency heating. The FDA allows an SAR of 0.4 W/kg averaged over the whole body (Department of Health and Human Services, FDA, 1982). Ex vivo exposure of large metal prostheses to fields over six times that experienced in MRI have not revealed any appreciable heating (Davis et al., 1981). To date, there has been no conclusive evidence that radiofrequency is a significant clinical issue in magnets up to 3 T.

The biological effect of MRI should be considered when offering parent-present induction; however, there are no reports implicating MRI-caused chromosomal aberrations. Studies in amphibians demonstrate that exposure to a 4-T magnetic field does not cause any defects in embryologic development (Prasad et al., 1990). Most hospital’s MRI machines are 1.5 T. Despite these studies, pregnant patients or family members are not usually allowed into the MRI scanner. MRI scans during pregnancy are discouraged by the ACR during the first and second trimesters unless fetal imaging is required or the MRI is necessary for emergent medical care (Woodard et al., 2006).

Additional safety issues for MRI include implanted objects (i.e., cardiac pacemakers), ferromagnetic attraction that causes objects to become projectile, noise, biological effects of the magnetic field, thermal effects, equipment issues, and claustrophobia. Some stainless steel may contain ferritic, austenitic, and martensitic components (Dujovny et al., 1985; Persson et al., 1985). Martensitic alloys contain fractions of a crystal phase known as martensite, which has a body-centered cubic structure, is prone to stress corrosion failure, and is ferromagnetic. Austenite is formed in the hardening process of low carbon and alloyed steels and has ferromagnetic properties. Iron, nickel, and cobalt are also ferromagnetic. For this reason, the components of any implanted device should be carefully researched before entering the magnet. Stainless steel or surgical stainless objects interacting with an external magnetic field may produce translational (attractive) and rotational (torque) forces. Intracranial aneurysm clips, cochlear and stapedial implants, shrapnel, intraorbital metallic bodies, and prosthetic limbs may move and potentially dislodge. Special precaution should be taken with cochlear implants in the 3-T environment, because unremovable magnets may suffer demagnetization in the scanner. These patients should only undergo imaging in the 3-T scanner after special precautions are taken (Majdani et al., 2008). Some eye makeup and tattoos may contain metallic dyes and therefore cause ocular, periorbital, and skin irritation (Scherzinger and Hendee, 1985; Prasad et al., 1990). Some tissue expanders employed in reconstructive surgery have a magnetic port to help identify the location for intermittent injections of saline (Liang et al., 1989). Bivona tracheostomy tubes usually contain ferrous material (although it is not specified in the package insert) and should be replaced with Shiley tracheostomy tubes before patients enter the MRI environment.

Cardiac pacemakers present a special hazard in and around the MRI scanner, especially in patients who are dependent on pacemakers. Most pacemakers have a reed relay switch that can be activated when they are exposed to a magnet of sufficient strength (Pavlicek et al., 1983). This activation could convert the pacemaker to the asynchronous mode. There are at least two known cases of patients with pacemakers who died from cardiac arrest while in an MRI scanner. The autopsy of one patient determined that the death was the result of an interruption of the pacemaker in the magnetic environment (Center for Disease and Radiological Health, 1989). In addition to the risk of pacemaker malfunction, there is also the chance that torque on the pacer or pacing leads may create a disconnect or microshock (Erlebacher et al., 1986). Recent studies demonstrate that with careful preparation, select patients with permanent pacemakers and implantable cardioverter defibrillators may safely undergo imaging in the 1.5-T environment without any inhibition or activation of their device (Nazarian et al., 2006). The ACR formed a Blue Ribbon Panel on MRI Safety in 2001 to review existing MRI safety practices and issue new guidelines. The ACR Guidance Documents for Safe MR Practices was published in 2002 and updated in 2004 and again in 2007 (Kanal et al., 2007). Safety concerns related to pediatric MRI were specifically addressed in the 2007 document, with specific emphasis on patient screening, sedation, and monitoring issues. Implanted cardiac pacemakers or implantable cardioverter defibrillators were considered a relative contraindication to MRI and only scanned in locations staffed with radiologists and cardiologists of appropriate expertise. The recommendation was for radiology and cardiology personnel, along with a fully stocked crash cart, to be readily available, as well as a programmer to adjust the device if necessary. After the MRI, a cardiologist should confirm function of the device and recheck it within 1 to 6 weeks. In general, heart valves are not ferromagnetic and are not a contraindication to MRI. It is critical that everyone entering the vicinity of the MRI scanner fills out a screening form that specifically lists every possible implantable device, alerting the MRI staff to any potential hazards.

The magnetic field may affect the electrocardiogram. The changes in the T wave are not the results of biological effects of the magnetic field but rather to superimposed induced voltages. This effect of the magnetic field on the T wave is not related to cardiac depolarization, because no changes to the P, Q, R, or S waves have ever been observed in patients exposed to fields up to 2 T. There are no reports of MRI affecting heart rate, ECG recordings, cardiac contractility, or blood pressure (Beischer, 1969; Tenforde et al., 1983; McRobbie and Foster, 1985; Gulch and Lutz, 1986). One study, however, found that humans exposed to a 2-T magnet for 10 minutes developed a 17% increase in the cardiac cycle length (CCL). The CCL represented the duration of the RR interval. The CCL reverted to preexposure length within 10 minutes of removing the patient from the magnetic field (Jehenson et al., 1988). The implications of this finding are unclear. This change in CCL in patients with normal hearts may be of no consequence. The implications of this finding for patients with fragile dysrhythmias or sick sinus syndrome, however, have yet to be determined.

In the presence of an external magnetic field, a ferromagnetic object can develop its own magnetic field and become a projectile object. The attractive forces that are created between the intrinsic and extrinsic magnetic fields can propel the ferromagnetic object toward the MRI scanner. Special note should be made of the magnet’s strength. Over the past few years, 1.5-T magnets have been supplanted by 3-T magnets. The field strength and magnetic force generated by a 3-T MRI scanner are unforgiving to the careless or inadvertent introduction of a ferrous object into the environment. Placing a magnet outside the MRI scanner can be a helpful but crude and sometimes inaccurate way to test any objects. If the object is not attracted to the magnet, this is not an absolute indication that there is no ferrous material present. A positive attraction, however, provides critical information to the anesthesiologist. Some unusual objects that have found their way into the MRI suite only to become projectile objects include a metal fan, a pulse oximeter, shrapnel, a wheelchair, a cigarette lighter, a stethoscope, a pager, a hearing aid, a vacuum cleaner, a calculator, a hair pin, an oxygen tank, a prosthetic limb, a pencil, an insulin infusion pump, keys, watches, and steel-tipped or heeled shoes (Kanal, 1992). Small objects can usually be easily removed from the magnet, but large objects may have so much attractive force to the MRI scanner that it is impossible to remove them by manual force. In these circumstances, quenching the magnet may be the only way to release the object once it is attached to the scanner. Quenching the magnet eliminates the magnetic field over a matter of minutes. This process is not without substantial risk; as helium gas is vented, condensation and considerable noise fill the suite. All personnel are required to vacate the suite during a quench, because there is a risk of hypoxic conditions if the helium should inadvertently enter the room.

In 2008, the JCAHO recognized the potential and existent hazards of the MRI environment when they published the Sentinel Event Alert (The Joint Commission, 2009). This alert identified 5 MRI-related cases of injury and 4 MRI-related deaths—one from a projectile and three cardiac events. The alert was designed to prevent accidents and injuries in the MRI suite, specifically identifying eight types of possible injuries (Box 33-1).

Box 33-1 The Joint Commission Sentinel Event Alert

Preventing accidents and injuries in the mri suite

“Missile effect” or “projectile” injury in which ferromagnetic objects (those having magnetic properties) such as ink pens, wheelchairs, and oxygen canisters are pulled into the MRI scanner at rapid velocity.
Injury related to dislodged ferromagnetic implants such as aneurysm clips, pins in joints, and drug infusion devices.
Burns from objects that may heat during the MRI process, such as wires (including lead wires for both implants and external devices) and surgical staples, or from the patient’s body touching the inside walls (the bore) of the MRI scanner during the scan.
Injury or complication related to equipment or device malfunction or failure caused by the magnetic field. For example, battery-powered devices (laryngoscopes, microinfusion pumps, monitors, etc.) can suddenly fail to operate; some programmable infusion pumps may perform erratically; and pacemakers and implantable defibrillators may not behave as programmed.
Injury or complication because of failure to attend to patient support systems during the MRI. This is especially true for patient sedation or anesthesia in MRI arenas. For example, oxygen canisters or infusion pumps run out and staff must either leave the MRI area to retrieve a replacement or move the patient to an area where a replacement can be found.
Acoustic injury from the loud knocking noise that the MRI scanner makes.
Adverse events related to the administration of MRI contrast agents.
Adverse events related to cryogen handling, storage, or inadvertent release in superconducting MR imaging system sites.

From The Joint Commission: Preventing accidents and injuries in the MRI suite, 2008. Available at http://www.jointcommission.org/SentinelEvents/SentinelEventAlert/sea_38.htm.

Special attention has recently been devoted to the topic of the IV gadolinium contrast that is used to enhance MR images. Gadolinium (in the form of gadopentetate dimeglumine) was approved by the FDA in 1998 as a contrast agent for MRI. With an elimination half-life of between 1.3 and 1.6 hours, gadolinium is excreted via the kidneys after forming a complex with chelating agents (Baker et al., 2004). Adults and children have similar elimination half-lives of gadolinium, with 95% excreted within 72 hours (Weinmann et al., 1984; Van Wagoner et al., 1990). Because gadolinium does not contain iodine, it does not produce an osmotic load and is generally considered safer and less allergenic than iodine (Brasch, 1993; Murphy et al., 1996; Dorta et al., 1997). Important warnings from the FDA suggest that patients with advanced kidney failure are at risk of developing nephrogenic systemic fibrosis or nephrogenic fibrosing dermopathy after gadolinium-based MR contrast agents. The FDA first notified health care professionals and the public about this risk in June 2006. There are currently five gadolinium-based contrast agents approved for use in the United States: Magnevist (gadopentetate dimeglumine), Ominiscan (gadodiamide); OptiMARK (gadoversetamide); MultiHance (gadobenate dimeglumine); and Prohance (gadoteridol). To date there are no reports of nephrogenic systemic fibrosis in those with normal kidney function or those with mild-to-moderate kidney insufficiency. The FDA suggests that gadolinium only be used when absolutely necessary in those with advanced kidney failure and that these patients undergo dialysis after vascular studies that require a large amount of gadolinium contrast.

Some patients experience claustrophobia and have difficulty cooperating during the study. Anxiety reactions are estimated to occur in 4% to 30% of patients (Granet and Gelber, 1990; Melendez and McCrank, 1993). As already discussed, new advances in technology now offer patients with anxiety or claustrophobia distraction with MRI-safe video goggles (Resonance Technology; Los Angeles, California). Patients with extreme skeletal abnormalities such as advanced scoliosis or flexion contractures, although motivated, may be unable to lie motionless or supine on the solid, uncushioned MRI table for the extended duration of a spinal MRI. These patients may require general anesthesia for positioning and comfort or may need adjunctive pain medication.

Nuclear Medicine

Nuclear medicine is one of the oldest functional imaging disciplines. Scans obtained through nuclear medicine are useful for identification of epileptic foci in refractory epilepsy, evaluation of cerebrovascular disease (e.g., Moyamoya disease), and the evaluation of cognitive and behavioral disorders (O’Tuama and Treves, 1993). Anesthesiologists become involved when the child’s medical history suggests that procedural sedation would not be appropriate. In order to complete these scans, the child must remain motionless for at least 1 hour.

The two most common nuclear medicine studies that require the administration of an anesthetic are single-photon emission computed tomography (SPECT) scans and positron emission tomography (PET) scans. SPECT scans use single-photon gamma-emitting radioisotopes and rotating gamma cameras to produce three-dimensional brain images. SPECT scans involve the use of radiolabeled technetium-99 (half-life, 6 hours), which has a high rate of first-pass extraction as well as intracellular trapping in proportion to regional cerebral blood flow (Chiron et al., 1989). SPECT scans are ideal when seeking seizure foci, and they often precede surgical resection of an identified focus. The technetium radionuclide is ideal because it remains intracellular and can be visualized on scan hours after a seizure has occurred. Ideally, the child should be scanned within 1 to 6 hours of the seizure. The radionuclides are physiologically harmless and not allergenic. Caregivers should, however, wear gloves to minimize contact with radiation-containing secretions.

PET scans use positron emission tomography and radionuclide tracers of metabolic activity, such as oxygen or glucose metabolism (Chugani, 1993; Griffeth et al., 1993). Unlike SPECT scans, PET scans should be performed during the seizure itself. Because of the short half-life of the glucose tracer (110 minutes), the scan is best completed during the seizure or within 1 hour thereafter.

Radiation Oncology

Pediatric radiation oncologists use ionizing photons to destroy lymphomas, acute leukemias, Wilms tumor, retinoblastomas, and tumors of the central nervous system. Multiple sessions are typical, requiring reliable motionlessness in order to precisely aim the beam at malignant cells while sparing healthy cells. A planning session in a simulator is often scheduled before the initiation of radiation therapy so that fields to be irradiated can be plotted and marked.

Radiation therapy is usually brief, nonpainful, and may be approached with a variety of plans for rendering the patient temporarily motionless. The key issue is the anesthesiologist’s limited access to the patient. Remote video monitoring, as well as ECG and pulse oximeter use, are crucial. Two, or in some locations three, video cameras are used to look at the monitors, the chest, and the face of the patient. A central venous catheter in young children undergoing a long course of radiation therapy helps immensely. It is important to remember that infants undergoing radiation therapy after a prolonged fast are at risk for hypoglycemia; delayed awakening, or tremulousness, any of which should prompt a glucose determination.

Fractionated radiation therapy is the strategy of dividing the total radiation therapy course into discrete daily sessions, allowing normal tissue repair between sessions while the tumor burden is lessened or destroyed. Hyperfractionated, or multiple-session daily radiation therapy, is a modality reported primarily in adults for head and neck cancers. The rationale for twice-daily fractionation in children is that fractionation to growing bone in rats reduces the growth deficit by 25% to 30%; the hope is that other normal tissues may be similarly spared during growth (Eifel, 1988; Eifel et al., 1990). Whereas one successful approach has been to give infants an initial formula feeding 6 hours before their first treatment and keep them fasting until recovery from their second anesthetic (6 hours after the first), with the current liberalization of fasting guidelines it is preferable to give children clear liquids during their recovery from the first anesthetic and keep them fasting thereafter for 4 hours before the second anesthetic (Menache et al., 1990).

Stereotactic radiosurgery (with a Gamma Knife) is a major advance in the treatment of select intracranial arteriovenous malformations and tumors in children (Loeffler et al., 1990). Stereotactic radiosurgery differs from external-beam radiotherapy in several important ways. A focused, single, large fraction of radiation is used instead of smaller, daily fractions. Stereotactic radiosurgery uses gamma rays of relatively weak intensity that are produced by 201 cobalt-60 sources that intersect at a single point where all 201 beams converge to destroy tumors, vascular malformations, or abnormal tissue sites within the brain. Normal brain tissue surrounding the abnormality is therefore relatively protected from radiation effects. In pediatrics as well as in adults, most radiosurgery originally concentrated on treatment of small, histologically benign lesions such as vascular malformations, acoustic neuromas, and pituitary adenomas. This has more recently been expanded to include malignant tumors such as solitary metastases, ependymomas, glioblastomas, and several other tissue types. For optimal results, the tumor’s volume should be small (14 cm3) (Coffey et al., 1992).

Stereotactic radiosurgery requires coordination between departments of radiology, radiation therapy, neurosurgery, and anesthesiology. The stereotactic procedure begins either during the CT or MRI scan. The child is placed in a stereotactic head frame that is screwed into the cranium. Most adults are able to tolerate this entire procedure with local anesthesia or sedation. The neurosurgeon infiltrates the skin with a local anesthetic before applying the head frame. Adults and older children who tolerate this procedure with sedation alone may vomit as a result of anxiety, headache, or the location of the tumor itself. Because the head frame is heavy and cumbersome, it is difficult for the vomiting patient to turn his or her head in order to protect his or her airway. Pediatric patients (including most adolescents) typically require a general anesthetic. General anesthesia with tracheal intubation is induced before placement of the head frame. The key for removal of the head frame is taped to the frame itself. A nasogastric tube is placed for the day’s anesthetic.

Calculations for dose and the three-dimensional coordinates for the beam may take several hours to compute after the initial radiologic study and head-frame placement. Some patients do well with sedation and spontaneous breathing; however, younger patients are usually mechanically ventilated. An initial CT scan is followed by computer calculations. Once the calculations are complete, the patient is transferred to the radiosurgery suite. After the irradiation, the patient is allowed to emerge from the anesthetic (Loeffler et al., 1990). The most common perioperative problem is nausea and vomiting, probably because of radiation sensitivity of the chemoreceptor trigger zone.

Stereotactic radiation therapy is a more precise localization of the fractionated radiation dose over the same duration of time as conventional radiation therapy, with the adjunctive use of a head frame. Considerations for the head frame include ease of application, reliability, ability to deliver supplemental oxygen and support the airway with a face mask if needed, and rapid removal of the facial restraint should it become necessary.

Total body irradiation (TBI) is generally performed twice a day over a 6-week period. It is usually in preparation for a bone-marrow transplant. For those patients who require anesthesia, the commitment is large—not only for the twice daily anesthetic but also for the coincident fasting status required. As these patients progress with their TBI treatment and become more immunocompromised, there is an increased risk of acquiring an illness during the course of treatment. Vomiting, respiratory illness, poor nutrition, or hypovolemia are all possible. Cancelling a TBI treatment because of an associated illness is discouraged, because it disrupts the course of treatment and could compromise the patient’s overall prognosis. Although anesthesiologists are wary of the risks of aspiration, both sedation and general endotracheal anesthesia have been found to decrease the incidence of vomiting with TBI (Westbrook et al., 1987; Whitwam et al., 1978).

Clinic and Office Procedures

Endoscopic Procedures

Gastrointestinal endoscopy has become a routine part of patient care, and as such it constitutes the bulk of procedures performed by a pediatric gastroenterologist (Fox, 1998). Depending on the patient and the type of procedure contemplated (therapeutic vs. diagnostic), children may require no sedation, minimal to moderately deep sedation, or general anesthesia. Minimal sedation may impair cognitive function and coordination while ventilatory and cardiovascular functions are relatively unaffected. However, pediatric patients often are uncooperative and do not tolerate endoscopic procedures with minimal or moderate sedation, necessitating deeper sedation or general anesthesia to successfully accomplish the procedure (American Society of Anesthesiologists Task Force on Sedation and Analgesia by Non-Anesthesiologists, 2002). Over the past 15 years, the volume of endoscopic procedures has increased by twofold to fourfold in the adult community, and has most likely increased at a similar rate in children (Cohen et al., 2006).

The inability to independently maintain ventilatory function and to respond purposefully increases the risk involved with deep sedation. Although some recommend that deep sedation be limited to anesthesiologist delivery only, gastroenterologists have demonstrated that they too are able to safely administer sedation (Saint-Maurice and Hamza, 1992; Wolfe and Rao, 1992; Hassall, 1993, 1994; Dillon et al., 1998; Bouchut et al., 2001; Koh et al., 2001; Paspatis et al., 2006). Propofol, considered by the ASA to be within the scope of anesthesia practice only, is considered by the American Society for Gastrointestinal Endoscopy (ASGE) to be an acceptable sedative for gastroenterologist administration (ASGE, 2002; Walker et al., 2003; Rex et al., 2005; Perera et al., 2006; Rex, 2006; Abu-Shahwan and Mack, 2007). Propofol is an important sedative for gastroenterologists, and it is estimated that one quarter of all adult endoscopies are performed with propofol sedation (Cohen et al., 2006). Children with more complex medical problems, anticipated airway difficulties, morbid obesity, or behavioral problems can undergo their procedures in the operating room. Regardless of the site of the procedure, all patients scheduled for endoscopy should be evaluated in advance to confirm that they are appropriate candidates. In addition, the anesthetic technique depends on the procedure, the patient, and the skill of the endoscopist, as well as the limitations and capabilities of the endoscopy suite. There is a wide range of sedation agents for children as well as adults, and there is no optimal sedation regimen for either age group (Lightdale et al., 2007).

Procedural sedation is readily achieved with an IV anesthetic combining a sedative (e.g., midazolam), opioid (e.g., fentanyl, alfentanil, remifentanil, or dexmedetomidine), and a hypnotic (e.g., propofol). Spontaneous ventilation without the patient’s airway being intubated has been shown to be a safe and effective technique (Bouchut et al., 2001; Koh et al., 2001; Koroglu et al., 2006). The majority of complications are respiratory and usually occur during an esophagogastroduodenoscopy (EGD). These complications include apnea, laryngospasm, bronchospasm, and airway obstruction. Bradycardia has been observed with dexmedetomidine use in children. Most problems resolve after withdrawal of the endoscope and positive pressure ventilation with a tightly-fitting mask; however, some patients may require endotracheal intubation to secure an airway and safely complete the procedure.

Esophagogastroduodenoscopy

Access to the airway is obviously limited once a transoral endoscope is in place. It is important to maintain spontaneous ventilation during deep sedation, because any airway intervention needed typically requires the removal of the endoscope. The two most stimulating portions of the EGD are transoral and transpyloric passage of the endoscope. A smooth endoscope insertion can be aided by topical spray of local anesthesia to the oropharynx to help eliminate coughing and gagging.

A majority of the respiratory complications noted previously occur during EGD when compared with colonoscopy, especially in infants and younger children. It has been suggested that this results from a combination of factors, including the large size of the endoscope and partial airway obstruction resulting in hypoxemia. Abdominal distention as a result of air introduced into the stomach may impair diaphragmatic excursion, leading to hypoventilation. This has led several groups to select 6 months of age, as a result of the higher respiratory complication rate in this age group, as the time before which general anesthesia with endotracheal intubation is required for the procedure (Wolfe and Rao, 1992; Koh et al., 2001).

Colonoscopy

Access to the airway is unimpeded during a colonoscopy. Deep sedation can be achieved more readily, and if respiratory problems occur, airway interventions are straightforward to manage. Patients undergoing colonoscopy also experience increased stimulation during certain parts of the procedure, such as when traversing the colon to the cecum. Also, at times, abdominal pressure is applied to help guide the colonoscope. The depth of the anesthetic should be adjusted accordingly.

Endoscopic Retrograde Cannulation of the Pancreas

Although many institutions report success of procedural sedation in pediatric patients undergoing endoscopic retrograde cannulation of the pancreas, general anesthesia with endotracheal intubation may make the procedure easier to perform, especially if the procedure is of long duration, the patient has significant comorbid diseases, or the procedure is performed with the patient in the prone position (Teng et al., 2000; Prasil et al., 2001).

Psychiatric Interviews

IV sodium amobarbital has a long history as an adjunct to psychotherapy, having found its peak use during World War II and immediately thereafter in helping soldiers deal with the stresses and trauma of combat (Zonana, 1979). Although this technique has enjoyed a resurgence for diagnostic and therapeutic interventions in adults, pediatric reports are rare. Weller et al. (1985) described the successful use of sodium Amytal in psychiatric interviews in prepubescent children. The induction of a tranquil state and sedation (e.g., slurred speech, a sense of fatigue, difficulty counting backwards, and basal vital signs) is similar to the anxiolysis achieved during monitored anesthesia care. A bispectral index (BIS) monitor may prove to be a useful adjunct as well (Palmer et al., 2001). The psychiatric interview process under these conditions is fascinating to participate in, if only as an observer. Memory retrieval, for instance the uncovering of relationships between current psychopathology and earlier traumatic life events, or symptom removal via therapeutic suggestions, are examples of interventions facilitated by the pharmacologically induced relaxed state made possible by the anesthesiologist during the interview.

Safety issues for patients and their anesthesiologists

As anesthesiologists find themselves participating in the care of patients who require increasingly sophisticated imaging technology, it is appropriate to examine the risks for patients and staff exposed to the types of high energies and contrast agents used.

Use of Intravascular Contrast Media

In a comprehensive review, Goldberg (1984) noted that approximately 5% of radiologic examinations with radiocontrast media (RCM) are complicated by adverse reactions, with one third of these being severe and requiring immediate treatment. Reactions occur most commonly in patients between 20 and 50 years of age and are relatively rare in children. The male/female ratio is about 2.5:1, not dissimilar to the gender distribution of other allergies such as latex, aspirin, and neuromuscular blocking agents. With a history of atopy or allergy, the risk of a reaction is increased from 1.5- to 10-fold. Reactions vary from mild, subjective sensations of restlessness, nausea, and vomiting to a rapidly evolving, angioedema-like picture accompanied by respiratory distress, bronchospasm, arrhythmias, and cardiac arrest. Because of the high osmolar concentrations of these agents (often higher than 1000 mOsm, and sometimes more than 2000 mOsm), caution should be exercised with patients who have a limited cardiovascular reserve (such as patients in congestive heart failure or those with cardiomyopathy). In addition, volume-depleted young children who have been kept fasting for prolonged intervals or who have had bowel preparations should be prehydrated before RCM administration. Those patients who are dependent on a full intravascular volume status (e.g., patients with sickle cell disease or restricted pulmonary circuit volume with cyanotic congenital heart disease and patients with arteriovenous shunts) should be monitored carefully for an initial rise in filling pressures and intravascular volume and subsequent diuresis after an osmolar load. Patients with impaired excretory mechanisms, such as those in renal failure, must be monitored closely after high osmolar loads. Low-osmolar RCM administrations are relatively safe with regard to life-threatening reactions, but moderate non–life-threatening reactions requiring some treatment occur 0.2% to 0.4% of the time, and a severe life-threatening reaction can occur in 0.04% of patients (Thomsen and Bush, 1998).

RCM contains iodine, because iodine’s high density and low toxicity make it an ideal agent for visualization and differentiation. The iodine is filtered through the glomeruli and is not reabsorbed by the glomeruli or the tubules. Because the contrast agent is hypertonic relative to plasma, an initial hypertensive response is usually followed by a hyperosmotic diuresis with the potential for hypotension. Equilibration with the extracellular fluid compartment occurs within 10 minutes, heralded by the onset of diuresis. Special attention should be paid when administering RCM with iodine to any child with a history of congestive heart failure. Patients with hepatic or renal dysfunction should be observed closely for signs of impaired excretion of the RCM. In sickle cell disease, the increase in blood osmolarity may precipitate shrinkage, clumping, and ultimately sickling of erythrocytes and vascular occlusion. Sickled cells are known to align with external magnetic fields to which they are exposed; it is unknown how this theoretic concern compares, for example, with the normal forces of deformation imposed on red cells of patients with sickle cell disease in their normal course through the vascular tree (Kanal et al., 1990).

Gadolinium diethylenetriaminepentaacetic acid (DTPA) is a low osmolar ionic contrast medium used for MRI, with a slower clearance in neonates and young infants than adults, yielding longer windows for imaging (Elster, 1990). Free gadolinium has a biological half-life of several weeks, with uptake and excretion taking place in the kidneys and liver. Unfortunately, free gadolinium is quite toxic and is therefore chelated to another structure that restricts the ion and decreases its toxicity. The most common adverse reactions are nausea, vomiting, hives, and headache. Local injection site symptoms include irritation, focal burning, or a cool sensation. Transient elevations in serum bilirubin (3% to 4% of patients) have been reported, and a transient elevation in iron for Magnevist and Omniscan (15% to 30% of patients) occurs, which tends to reverse spontaneously within 24 to 48 hours (Van Wagoner and Worah, 1993). Anaphylactoid reactions occur on the order of 1:100,000 to 1:500,000 and are more rare (< 1:100,000 doses) in children.

The older literature states that patients who have had anaphylactic reactions to shellfish are at increased risk of anaphylactoid reaction to RCM. The irony of the statement is that it may be correct, but not for obvious reasons. The original rationale was that shellfish contain high quantities of iodine, and therefore it was assumed that there would be a risk of cross-reactivity. However, neither shellfish allergy nor RCM reactions are caused by iodine. Atopy is a risk factor; therefore, the association between atopy, anaphylactic reactions to shellfish, and a possible predisposition to a RCM reaction may indeed be valid.

The treatment of severe allergic reactions, whether anaphylactoid or anaphylactic, is no different than for any other allergic reaction. Epinephrine, aminophylline, atropine, diphenhydramine, and steroids have all been employed in order to control varying degrees of adverse reactions. A patient who requires RCM administration and who has had a previous reaction to RCM has an increased (35% to 60%) risk for a reaction on reexposure. Pretreatment of these high-risk patients with prednisone and diphenhydramine 1 hour before RCM administration reduces the risk of reactions to 9%; the addition of ephedrine 1 hour before RCM administration further reduces the rate to 3.1% (Kelly et al., 1978; Greenberger, 1984).

In 2007, the ACR updated their practice guidelines for the use of intravascular contrast media that they published in the Manual on Contrast Media (ACR, 2008). Iodinated low-osmolality contrast media have a lower incidence of adverse effects as compared with ionic high-osmolality contrast media. The management of acute reactions in children is clearly outlined by the ACR (Box 33-2).

Box 33-2 Management of Acute Reactions in Children

Urticaria

No treatment needed in most cases
Give H1-receptor blocker: diphenhydramine PO, IM, or IV 1 to 2 mg/kg, up to 50 mg.
If severe or widely disseminated: give α-agonist, epinephrine SC (1:1000) 0.01mL/kg.

Facial edema

Give O2 6 to 10 L/min (via mask, face tent, or blow-by stream). Monitor electrocardiogram, O2 saturation (pulse oximeter), and blood pressure.
Give α-agonist: epinephrine SC or IM (1:1000) 0.01 mL/kg, up to 0.3 mL/dose. Repeat in 15 to 30 minutes as needed.
Give H1-receptor blocker: diphenhydramine IM or IV 1 to 2 mg/kg, up to 50 mg.
If not responsive to therapy, seek appropriate assistance (e.g., cardiopulmonary arrest response team).

Laryngeal edema or bronchospasm

Give O2 6 to 10 L/min (via mask, face tent, or blow-by stream). Monitor electrocardiogram, O2 saturation (pulse oximeter), and blood pressure.
Give β-agonist inhalers: bronchiolar dilators, such as metaproterenol, terbutaline, or albuterol, 2 to 3 puffs. Repeat as necessary.
Give epinephrine SC or IM (1:1000) 0.01 mL/kg, maximum 0.3 mL/dose or IV epinephrine (1:10,000) 0.1 mL/kg, maximum 3 mL/dose. Repeat in 3 to 5 minutes as needed.
Call for assistance (e.g., cardiopulmonary arrest response team) for severe bronchospasm or if O2 saturation <88% persists.

Pulmonary edema

Give O2 6 to 10 L/min (via mask, face tent, or blow-by stream). Monitor electrocardiogram, O2 saturation (pulse oximeter), and blood pressure.
Give diuretic: furosemide IV 1 to 2 mg/kg.
Call for assistance (e.g., cardiopulmonary arrest response team).

Hypotension with tachycardia

Give O2 6 to 10 L/min (via mask). Monitor electrocardiogram, O2 saturation (pulse oximeter), and blood pressure.
Legs elevated 60 degrees or more (preferred) or Trendelenburg position.
Keep patient warm.
Give IV or IO normal saline or lactated Ringer’s solution 20 mL/kg over 5 to 10 minutes. Bolus infusion over 10 to 20 minutes in patients with myocardial dysfunction.
Seek appropriate assistance (e.g., cardiopulmonary arrest response team).

Hypotension with bradycardia (vagal reaction)

Give O2 6 to 10 L/min (via mask). Monitor electrocardiogram, O2 saturation (pulse oximeter), and blood pressure.
Legs elevated 60 degrees or more (preferred) or Trendelenburg position.
Keep patient warm.
Give IV or IO normal saline or lactated Ringer’s solution 20 mL/kg over 5 to 10 minutes. Give infusion over 10 to 20 minutes in patients with myocardial dysfunction.
Give atropine IV 0.02 mg/kg if patient does not respond quickly to steps 2, 3, and 4. Minimum initial dose of 0.1 mg. Maximum initial dose of 0.5 mg (infant/child), 1 mg (adolescent). Atropine dose may be doubled for second administration.
Seek appropriate assistance (e.g., cardiopulmonary arrest response team).

IM, Intramuscular; IO, intraosseous; IV, intravenous; SC, subcutaneous; PO, orally.

From American College of Radiology 2008 “Manual on Contrast Media.” Version 6. Reston, Va, p 75-76.

Allergic reactions rarely occur with oral agents. The incidence of severe anaphylactoid reactions to gastrointestinally administered agents is approximately 1:2,500,000, and the causes remain unknown. There are no pretreatment protocols established for these types of reactions and no well-defined risk factors. Gastrointestinal complications include nausea, vomiting, and diarrhea. One of the factors that may protect against having an allergic reaction is the poor absorption of oral iodinated contrast agents. Indeed, disruption of the GI mucosa is recognized as causing an increase in absorption of oral contrast, and the urinary excretion of contrast in a gastrointestinal study is a well-recognized sign. However, these signs are rarely associated with bronchospasm, flushing, periorbital edema, pruritis, rash, rhinitis or urticaria.

Ionizing Radiation

Radiation exposure is directly proportional to the duration of the procedure and inversely proportional to the square of the distance from the source. Henderson et al. (1991) monitored the radiation exposure of 16 pediatric anesthesia fellows during a – month period. Fellows assigned to the cardiac catheterization laboratory had a fluoroscopy exposure time of 14 to 85 minutes per case, typically for two to three cases per day. For these anesthesiologists, badge readings ranged from 20 to 180 mrem/month. All noncardiac anesthesia fellows had undetectable (<10 mrem/month) levels. All fellows wore lead aprons, 50% wore a thyroid shield, and one stepped at least 10 feet away from the source during every exposure; this latter fellow had a reading of 30 mrem, despite having spent 26 hours in the catheterization laboratory. The annual maximum permissible dose (MPD) for nonradiation workers (including anesthesiologists) is 100 mrem or 1 mSievert (mSv, Systeme Internationale Units). For comparison, the MPD for radiation workers is 50 mSv annually and 10 mSv times age cumulatively. MPD during pregnancy for radiation workers (per gestation) is 5 mSv. Limits of exposure and comparative sources of exposure are listed in Table 33-2.

TABLE 33-2 Limits and Sources of Radiation Exposure

Limits for Exposures Exposure Range
Occupational dose limit (U.S. NRC) 5000 mrem/year  
Occupational exposure limits for minors 500 mrem/year  
Occupational exposure limits for fetus 500 mrem  
Source of exposure    
Average dose to U.S. public from all sources 630 mrem/year  
Average dose to U.S. public from natural sources 330 mrem/year  
Average dose to U.S. public from medial sources 53 mrem/year  
     
Chest x-ray 8 mrem 5-20 mrem
Extremities x-rays 1 mrem  
Dental x-ray 10 mrem  
Head/neck x-ray 20 mrem  
Cervical spine x-ray 22 mrem  
Lumbar spinal x-rays 130 mrem  
Pelvis x-ray 44 mrem  
Hip x-ray 83 mrem  
Upper GI series 245 mrem  
Lower GI series 405 mrem  
CT (head and body) 1100 mrem  
Expected 50% death without medical attention 400,000 mrad 300,000-500,000 mrem
Doubling dose for genetic effects 100,000 mrad  
Doubling dose for cancer 500,000 mrad (8% per mSv, natural level at 20%)
Dose for increase cancer risk 1:1,000 1250 mrem (8% per mSv)
Consideration of therapeutic abortion threshold (dose in utero) 10,000 mrem  

1 mrem = 10 mSv; 1 rad is the amount of radiation to deposit 0.01 joules of energy per kilogram.

NRC, Nuclear Regulatory Commission; U.S., United States.

High-Intensity Magnetic Fields

MRI exposes the patient (and the health care workers surrounding the patient) to a static magnetic field, a rapidly switched spatial-gradient magnetic field, and radiofrequency magnetic fields. The static magnetic field, which causes alignment of unpaired tissue protons, may cause movement of ferromagnetic devices such as vascular clips, ventricular shunt connectors, casings for pacemakers, and control devices for pacemakers. Metallic devices in other areas, particularly when invested with fibrous tissue, are less problematic (Shellock and Crues, 1988; Shellock, 1989). As mentioned previously, tissue expanders may have magnetic ports to facilitate identification of the injection site. Despite their low mass, such ports have a potential for torque and movement in the presence of a strong magnetic field; therefore, the specific type of tissue expander should be identified before patient evaluation in an MRI (Liang et al., 1989). Assessment of risk in patients with implants or other possibly ferromagnetic devices or objects consists of a careful history including penetrating wounds, physical examination to look for scars, and possibly a plain radiograph of the region in question (Pohost et al., 1992). Other concerns have been increased blood pressure, cardiac arrhythmias, and impaired mental function. Although described or theorized on an experimental basis, little clinical documentation is available.

The magnetic field generates an electrical current two to three orders of magnitude less than a defibrillator (10 mA/M2, compared with, 000 to 10,000 mA/M2). This current strength may nevertheless reprogram a programmable pacemaker and interfere with its function (Erlebacher et al., 1986). Exposure to a strong external magnetic or electromagnetic field can lead to conversion of a demand pulse generator from synchronous to asynchronous mode, damage to the reed switch (that activates the fixed- rate pulse generator), reprogramming of pacemaker parameters, induction of currents in the electrode wires, or displacement of the generator itself. Indeed, it is the sensitivity of some reed switches that has determined the safety boundary of MRI devices as being 5 Gauss (5 × 10-4 T). Patients with implantable defibrillators or cardioverters, implantable infusion pumps (e.g., for insulin), cochlear implants, and neurostimulators are all at risk for having the implant device reprogrammed on exposure to the magnetic field. Defibrillator failure has been reported in the MRI environment (Snowdon, 1989).

Radiofrequency pulses cause heat production in metallic implants and coiled wires such as ECG cables or pulse oximeter cables if they are looped and laying on the patient’s skin. Patients with compromised thermoregulatory abilities, such as those with cardiac problems, fever, or taking certain drugs, may be at particular risk. Included in this group are infants, whose SAR is greater than that of adults because of the greater ratio of body surface area to body mass, and whose thermoregulatory abilities may be interfered with during a general anesthetic (Kussman et al., 2004). SAR refers to the energy absorption (e.g., increasing body temperature) with an increase in the total amount of radiofrequent energy absorbed (Fitzsimmons, 1992).

Increased reports of vertigo, nausea, and a metallic taste have been found in a study on human exposure to the 4-T magnetic field of a whole-body scanner (Schenck et al., 1992). Fertilized frog embryos exposed to a 4-T magnetic field did not demonstrate any adverse effects on early development (Prasad et al., 1990). An increase in CCL of 17% was found in healthy volunteers in a 2-T environment after 10 minutes of exposure, causing speculation about the effect of the 2-T environment on the sinus node (Jehenson et al., 1988). This may be of particular concern in patients with a preexisting arrhythmia history. Of more significant concern in pediatric patients is the potential for hypothermia, because of the air flow directed through the scanner cavity and the inability to control room temperature or use radiant warmers. The use of warm IV fluid bags, thermal packs, and blankets can decrease heat loss. Excellent reviews of monitoring considerations and equipment choices in the MRI environment, as well as patient safety principles are available, and the ACR (with a representative from the ASA) has published a recent white paper on MRI safety (Kanal et al., 1990, 2007; International Non-Ionizing Radiation Committee of the International Radiation Protection Association, 1991; Fitzsimmons, 1992; Menon et al., 1992; Patteson and Chesney, 1992; Pohost et al., 1992).

MRI and spectroscopy do not employ ionizing radiation. However, secondary harmful effects, such as magnetic objects becoming projectiles within the magnetic field as they approach the bore of the magnet and potentially causing injury, are a consideration (Chu and Sangster, 1986; Chaljub et al., 2001). Patients (and anesthesiologists) with metallic implants such as vascular clamps, hemostatic clips, dental devices, heart valve prostheses, intravascular coils, filters and stents, ocular implants, orthopedic implants, otologic implants, shrapnel, penile implants, and vascular access ports must be individually evaluated for their risk in the MRI environment (Cahalan et al., 1987; Shellock and Curtis, 1991).

As with individual precautions, equipment precautions should be taken for all ferromagnetic objects such as IV stands, oxygen, and nitrous oxide cylinders, and monitoring equipment. The anesthesia machine, if used in the scanning room, should be outfitted with aluminum gas cylinders and kept in the corner of the room. Anesthesia machines especially designed to be MRI-compatible are now readily available.

Difficult-airway management in the radiology suite

If a child with a known difficult airway requires endotracheal intubation in order for the scheduled procedure to be completed, it is wise to perform the anesthetic induction in the operating room, an area where access to difficult-airway equipment is readily available. Regardless of an anesthesiologist’s comfort level and familiarity with extramural environments, the same depth of back-up coverage is simply not available.

The unrecognized difficult airway is problematic in a remote location; therefore, it is important to have LMAs stocked in all extramural anesthesia carts. If a child cannot be intubated or ventilated with a mask, LMAs can provide a successful alternative. Case reports describe the successful use of LMAs in children with difficult craniofacial anomalies, such as Goldenhar’s syndrome and even Pierre Robin sequence (Fan et al., 1995; Hansen et al., 1995; Haxby and Liban, 1995). Similarly, a light wand may facilitate endotracheal intubation in the child with a difficult airway (Holzman et al., 1988). Recently introduced rigid laryngoscopes with video in infant through pediatric sizes (e.g., Glidescope), should be strongly considered for availability in offsite locations.

It is important to recognize that an airway that was not difficult on induction may become difficult on emergence after sclerotherapy with alcohol and subsequent tissue edema, particularly at the base of the tongue, neck, or the mediastinum (Furst et al., 1996; Ohlms et al., 1996; Fishman, 1999). These patients often require several days of airway support and ongoing evaluation in the ICU until airway swelling is no longer a concern.

Blood-loss management outside of the operating room

Transfusion requirements are rare in extramural locations, yet preprocedural anemia, accidental perforation of vascular structures, or medical transfusion requirements such as sickle cell disease or prematurity may require transfusion therapy. Equipment familiar to the anesthesiologist and identical to that available in the operating room is a welcome sight in a life-threatening emergency. Calling for additional help, establishing additional vascular access, and coordinating with the blood bank is crucial. Having a runner available may be critical when there is no equivalent to a circulating nurse. In an emergency, it may become necessary to involve a surgeon and transport the patient to the operating room, in which case it would be optimal for another anesthesia team to set up the operating room while the patient is being prepared for transport.

Summary

The demand for anesthesia and sedation services in sites distant to the operating room is continuing to increase. Providing patient services in locations remote to the operating room can be challenging and poses risks that may not exist in the operating-room setting. Although the incidence of adverse outcomes for anesthesia and sedation in these remote areas has never been prospectively studied, we can look at office-based and ambulatory surgery centers to extrapolate the risk. Comparative outcomes analysis in Florida reveals that the incidence of adverse events is higher in the office-based setting when compared with outpatient surgical centers (Vila et al., 2003). Although these outcomes cannot be directly compared, it raises the question of added risk in the off-site anesthetizing location. Sedation, monitored anesthesia care, and general anesthesia are all choices that carry risks. Historically, an avoidance of a general anesthesia has been thought to minimize the risk of adverse outcome. Closed-claims analysis has shown, however, that monitored anesthesia care poses an equal risk to general anesthesia with respect to severity of injury, death, and permanent brain damage. Furthermore, 24% of all monitored anesthesia care claims involve oversedation and respiratory depression (Bhananker et al., 2006). In summary, anesthesia care providers must recognize that as the demand for off-site services increases, so also should their ability to understand the environment and do careful risk analysis when selecting patients and formulating a plan of care.

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