Personnel Requirements

The environment and the demands of providing anesthesia outside of the OR are unique regardless of the specific organization that has been chosen for NORA. To create the kind of functioning sedation microsystem discussed earlier, several common themes lead to optimal safety and effectiveness of off-site anesthesia care:

Specific Environmental Requirements

Equipment (see earlier discussion) and monitoring standards (see later discussion) must meet those of the main OR environment. Regardless of whether the anesthetizing location is inside or outside the OR, the ASA has established minimum standards for equipment, monitors, and conditions of anesthesia delivery. These guidelines may, of course, be exceeded at any time based on the judgment of the involved anesthesia personnel. The ASA specifically requires that remote locations must have two sources of oxygen (O₂) (preferably a central source of piped O₂ and a backup E cylinder), suction, an anesthesia machine if administering inhalational anesthetics, a scavenging system for waste anesthetic gases, a self-inflating hand resuscitator bag able to deliver 90% O₂ and positive-pressure ventilation, standard of care monitors and equipment,^7,8 and sufficient electrical outlets, illumination, and space. The ASA Standards for Basic Anesthetic Monitoring include the following:

In addition, it is important to make further adaptations in the non-OR setting. Duplicates of critical equipment, such as laryngoscope handles and blades, should be immediately available. In the MRI unit, it is essential to have MRI-compatible laryngoscope blades and handles, as well as compatible monitoring devices. Each site should be carefully evaluated for important items, such as presence or absence of wall-delivered gases (O₂, nitrous oxide [N₂O], and air), location of suction equipment, and Ambu bag. Every site must have backup gas supplies. If pipeline O₂ is not available, O₂ should be drawn from H cylinders (6600 L) rather than the smaller E tanks (659 L).

Many off-site areas do not have wall suction, especially in the MRI environment. MRI-compatible wall suction is not widely available. An alternative method for providing suction in the MRI suite is to mount a suction canister with 30 feet of suction tubing outside the scanner room.⁹ The suction tubing can then be threaded through a hole in the console wall to access for use in the MRI unit.

Scavenging systems should be carefully evaluated in out of OR locations. When passive scavenging is not possible, active scavenging may be developed by using the wall-source vacuum or wall suction canisters. Ideally, a scavenging system dedicated solely to waste gases should be present.

Electrical circuitry in off-site locations must be upgraded to meet OR standards. Specifically, although the outlets tend to be grounded and hospital grade, plug and outlet incompatibility may be a problem. Adapters and conversion plugs must be available. Although off-site locations tend not to have as great a risk of electrical shock or electrocution to the child as in the OR, it is important to remember that these sites do not have line-isolation monitors. In the event of excessive leakage of current, the anesthesiologist would not be warned. Although the National Electrical Code no longer requires line-isolation monitors in nonflammable anesthetizing locations, it is strongly recommended in areas with multiple power sources. To ensure child and health care personnel safety, biomedical engineers must be attentive to the safe maintenance of all electrical equipment.

It is in the nature of off-site anesthesia that the physical environment and practice patterns are typically that of another medical specialty. It should also be noted that these other specialties practice under standards developed by their own professional organizations that apply to the procedures within their locations reflecting the different procedure goals. The varying specialties involved include (but are not limited to) gastroenterology, dentistry, cardiology, oncology, intensive care, emergency medicine, and radiology.¹⁰ Anesthesia providers who work in these environments are well served by familiarizing themselves with the standards for the given specialty area they are working in, as published on the individual websites for the various professional organizations.

Computed Tomography

CT involves ionizing radiation and can provide a good modality for differentiating between high-density (calcium, iron, bone, contrast-enhanced vascular and cerebrospinal fluid [CSF] spaces) and low-density (O₂, nitrogen, carbon in air, fat, CSF, muscle, white matter, gray matter, and water-containing lesions) structures. Because the scan time for current devices is brief, with actual imaging time ranging from 5 to 50 seconds per sequence, many children are able to tolerate CT without sedation or anesthesia. In cases in which anesthesia is required, it is often for those who have a fragile or unstable respiratory or cardiovascular status. Anesthesia or sedation is often required for children who are unable to cooperate (cognitively impaired children and those younger than 2 to 3 years of age) or require CT emergently. Emergent indications for CT include head trauma, unstable respiratory status in need of a pulmonary diagnosis, unexplained changes in mental status, or neoplasm workup in severely debilitated children. Anesthesia management is also necessary with a potentially unstable airway (peritonsillar abscess, anterior mediastinal mass, craniofacial anomaly, tracheoesophageal fistula, uncontrolled vomiting, or gastroesophageal reflux), or the need for breath holding during acquisition of images (three-dimensional dynamic airway studies) (Figs. 45-1 and 45-2). Some CT units are particularly concerned about children moving when contrast is injected (because of dose restrictions the contrast injection cannot be repeated) and therefore request anesthesia services for any child they cannot confidently predict will stay motionless for the study.

FIGURE 45-1 Three-dimensional dynamic computed tomography scan demonstrating change in caliber of left main-stem bronchus (circle) in an intubated child at end-inspiration (pressure held at 15 to 18 mm Hg) (A) versus end-expiration (B).

FIGURE 45-2 Three-dimensional CT scan demonstrating change in caliber of left main-stem bronchus (arrows) on inspiration (A) versus expiration (B).

Children with Down syndrome present a particular area of interest for the anesthesiologist working with the CT scanner. These children pose a unique risk for atlantoaxial instability and may require a head or neck CT to evaluate cervical and temporomandibular anatomy, recurrent sinusitis, or choanal atresia. The incidence of atlantoaxial instability varies from 12% to 32%.²⁵ Many children with Down syndrome require cervical spine radiographs before entering grade school or participating in the Special Olympics. Usually, the parents know the outcome of these tests and can relay the results of cervical spine radiographs. These studies alone do not indicate to the practitioner whether the child is at risk of dislocation.²³ Rather, it is the presence of neurologic signs or symptoms that would herald a spine that is “at risk”: abnormal wide-based gait, incontinence, increased clumsiness, fatigue with ambulation, complaints of numbness, tingling in an extremity, weakness of an extremity, or a new preference for sitting games. In infants, these clinical signs may be difficult to assess. In younger children, developmental milestones (e.g., crawling, sitting up, reaching for objects) should be evaluated. Physical signs may include clonus, hyperreflexia, quadriparesis, neurogenic bladder, hemiparesis, ataxia, and sensory loss. Children with atlantoaxial instability on a radiograph are at less risk for dislocation if they do not exhibit any signs or symptoms of instability. Children who are capable of following commands are asked to perform full neck flexion and extension maneuvers to determine whether pain, sensory, or motor manifestations of cord compression develop.

Perhaps the most controversial issue facing anesthesiologists with regard to CT scans is the issue of oral contrast for CT. Because children lack abundant retroperitoneal fat, they do not have the natural contrast needed to elucidate abdominal images. For this reason, children may be required to ingest (orally or via nasogastric tube) diatrizoic acid (Gastrografin) to opacify the stomach and bowel. Oral contrast is useful in the identification of an intraabdominal abscess, mass, fluid collection, bowel injury, pancreatic injury, or other traumatic injury. The oral contrast comes as Gastrografin 3% and may be diluted to a 1.5% to 2.5% strength concentration. Gastrografin 3% is the full-strength concentration; in this undiluted form, Gastrografin is hypertonic (2200 mOsm/L). At this concentration, it can cause pulmonary edema, pneumonitis, osmotic effusions, and death if aspirated. Fortunately, when Gastrografin is administered to children for CT it is diluted to 1.5% to 2.5% strength, which is thought to be much less dangerous if aspirated. The volume of oral contrast that is administered can be quite large. Neonates typically receive 60 to 90 mL. Infants between 1 month and 1 year of age may receive up to 240 mL. Children between the ages of 1 and 5 years receive between 240 to 360 mL of contrast medium. Risk is introduced when these children require anesthesia within an optimal window after ingestion (usually 30 minutes to 1 hour after receiving the contrast agent) to enhance visualization. By most fasting guidelines (nil per os [NPO]), Gastrografin consumption within 1 to 2 hours of an anesthetic or sedation does not fall within the usual NPO guidelines. Yet, the scan must be completed while the Gastrografin is present in the gastrointestinal tract. Despite the large volume of Gastrografin that may be ingested, there does not appear to be a significant aspiration risk in this population, and many anesthesiologists do not secure the airway with a tracheal tube (Fig. 45-3). A review of the pediatric and adult literature confirms that over the last 35 years only a few case reports have been published of aspiration syndrome attributed to Gastrografin, all in extremely high-risk patients.^24–26 Several investigators have evaluated this issue from different perspectives. In one study, a cohort of 50 patients who received oral contrast after blunt abdominal trauma were evaluated for radiologic evidence of aspiration pneumonia or clinical complications of aspiration.²⁷ Some of the patients received general anesthesia, and some were neurologically impaired (including several with increased intracranial pressure). In this very high-risk group, only one patient had a question of aspiration on a chest radiograph after the CT scan, and that patient did not develop pulmonary symptoms. Another study evaluated the volume of gastric contents of 365 patients undergoing deep sedation or general anesthesia for abdominal CT scans.²⁵ Gastric contents exceeded 0.4 mL/kg in 49% of those who received gastric contrast. Two cases of vomiting were recorded. None of the patients in the study developed clinical evidence of aspiration. When dilute Gastrografin is used, the risks associated with pulmonary aspiration appear to be small, even in children who are moderately to deeply sedated.²⁸ In spite of this evidence, no large cohort studies have been conducted that have the power to determine the actual incidence of aspiration in this setting. Therefore no accepted standard of care for the airway management of these children has been determined. Some anesthesiologists induce anesthesia with an intravenous or inhalational technique and maintain the anesthetic without securing the airway with a tracheal tube. Others perform rapid-sequence induction and tracheal intubation. The lack of consensus among anesthesiologists and the absence of evidence preclude a clear and consistent recommendation for managing the airway in these children.

FIGURE 45-3 Four hours after ingestion of Gastrografin, oral contrast is still present in the stomach and small intestine. Although dilute Gastrografin is still frequently present in the stomach at the time of computed tomography, there are as yet no case reports validating an increase in risk of pulmonary aspiration.

Nuclear Medicine

Nuclear medicine is one of the oldest functional imaging disciplines. Because of the advances in instrumentation and radiopharmaceuticals, nuclear scanning is becoming an increasingly popular imaging modality. Nuclear imaging can be used to evaluate an incredible range of pathologic conditions. These scans are useful for identification of the extent of disease for a large number of neoplasms.²⁹ They can also be used to detect epileptic foci in refractory epilepsy, evaluate cerebrovascular disease (e.g., moyamoya disease) and cognitive and behavior disorders, and detect and delineate renal function and disease, including detection of reflux and acute pyelonephritis.²³ Improvements in the hardware for nuclear imaging has greatly decreased the scan time, although even with the advent of two-level emission and transmission scans and combined CT imaging, a child must remain motionless for 20 to 60 minutes. The nuclear medicine environment is quiet, and the scan is pain-free. Accordingly, the indications for anesthesia or sedation include only those children who could not be reasonably expected to hold still for the 20 to 60 minutes, such as those with cognitive or behavioral impairment, young age, or severe pain or who are claustrophobic.²⁹ Sedation providers should be aware that the equipment in nuclear medicine imaging emits no ionizing radiation, but rather the radiation is contained within the child and is of very low energy levels. Depending on the nature of the study, the children require intravenous access for administration of the nuclear tracer well in advance of the scan and therefore usually have intravenous access for the anesthesia or sedation. Many nuclear scans also require an empty bladder to avoid interference from concentrated tracer in an enlarged bladder. Accordingly, the bladder is often catheterized after anesthesia is induced and the radioactive urine that is collected is disposed of in a radioactive-safe manner.

Two relatively new nuclear scans that involve anesthesia and present particular challenges are single-photon emission computed tomography (SPECT) 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-99m (half-life of 6 hours), which has a high rate of first-pass extraction and intracellular trapping in proportion to regional cerebral blood flow. This scan is useful for localizing seizure foci. It appears to be as accurate as invasive direct cortical mapping in this regard.³⁰ Injection of the radionuclide during a seizure will tag areas of increased cerebral blood flow and localize the seizure foci. The child should be scanned within 1 to 6 hours of the seizure and injection of the tracer. Logistically this can pose a problem because there is no way to predict exactly when a seizure will occur. Therefore the neurology service needs to communicate to the anesthesiology service the importance of being flexible in providing anesthetic services within the window of time allowed to complete the test whenever the next seizure occurs.

PET scans use radionuclide tracers of metabolic activity such as O₂ usage and glucose metabolism. Radionuclide tracers of glucose may be useful when seeking seizure foci or tumor recurrence.^29,31,32 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. The logistical problem in providing this service is even more difficult than that of SPECT scans. In addition to the need to have a team available to provide anesthesia on very short notice, there is a risk of hypovolemia, especially in infants, who remain on NPO status and without intravenous hydration while anticipating a seizure. It is therefore important to work with the neurology and neurosurgery services to plan these scans in advance, to ensure intravenous access to avoid hypovolemia, and to arrange anesthesia coverage when needed.

Stereotactic Radiosurgery

Stereotactic radiosurgery (gamma knife) is a major advance in the treatment of selected malignant tumors (ependymoma, glioblastomas), vascular malformations, acoustic neuromas, and pituitary adenomas in children.^33,34 Radiosurgery is indicated, especially for those children with a tumor located deep in the brain or in an area that could put the child at significant surgical risk (e.g., speech, motor, cerebellum, brainstem areas) or for the recurrent brain tumor that has failed prior treatment. Radiosurgery involves the use of a single large fraction of radiation that is directed at a specific target with minimal radiation exposure to the surrounding normal tissues. Optimal results are achieved with small tumor volumes (14 cm³ or less).³⁵

Stereotactic radiosurgery requires the coordination of the departments of radiology, radiation therapy, and anesthesiology. The procedure averages 9 hours but can take up to 15 hours. The stereotactic portion of the procedure begins in the morning in a CT scanner. A stereotactic head frame is applied after induction of general anesthesia and tracheal intubation. Some older children can tolerate the application of the head frame with local anesthesia alone but then develop anxiety because the pressure sensation produced by the head frame that can lead to anxiety, nausea, or vomiting. The vast majority of children require general anesthesia for application of the frame and subsequent imaging and surgery. When the head frame is in place, the key to unlock and remove it should be taped to the frame itself, in the event of a situation necessitating its emergent removal (e.g., vomiting, airway obstruction, or accidental tracheal extubation). For smaller children, nasal intubation may be considered to provide better stability during transport from the radiology suite to the OR. After the head frame is in place and the imaging study is completed, the child is transported (trachea intubated, sedated, and appropriately monitored) to the postanesthesia care unit while the radiologists and neurosurgeons review the images and plan radiosurgery. The postanesthesia care unit stay can range from 3 to 5 hours, during which time these children require continuous physiologic monitoring.

After the images are reviewed and the radiosurgery planning is complete, the child is transported to the stereotactic radiosurgery linear accelerator for treatment. In the treatment room full anesthesia monitoring and an anesthesia machine are present. To minimize radiation exposure to health care personnel, only the child remains in the scanner during treatment, observed at a distance with video cameras focused on both the child and monitors. The actual treatment lasts approximately 1 hour.

After radiosurgery is completed, the child is returned to postanesthesia care unit, where the trachea is extubated under controlled conditions. Risks are inherent with this prolonged anesthesia, which requires multiple transports between sites. One study examined 68 radiosurgery procedures in 65 children and reported four potentially serious anesthesia-related events.³⁶ In those children who received general anesthesia, serious complications included obstruction of the tracheal tube while in the head frame and lobar collapse requiring prolonged mechanical ventilation.

Radiation Therapy

Radiation therapy for children uses ionizing photons to destroy lymphomas, acute leukemias, Wilms tumor, retinoblastomas, and tumors of the central nervous system. Improved three-dimensional imaging and enhanced computing power have allowed radiation oncologists to conform radiation dose to the shape of the tumor and minimize radiation to the surrounding tissues.³⁷ The energy absorbed by the tissues is measured in grays (Gy), which has replaced the term rad. One Gy is equivalent to 100 rad. Although most children receive standard x-ray therapy, specific lesions may respond better to bombardment with electron, proton, or neutron beam therapy. The anesthetic considerations are identical regardless of the type of therapy in this respect.³⁸ A planning session in a simulator is typically scheduled before the initiation of radiation therapy to map the fields that require irradiation while the child is in a fixed position. For proton beam treatments, a planning session is carried out in a CT scanner. A fiberglass immobilization cast of the head is made while the child is anesthetized with propofol and with a natural airway (Fig. 45-4). This cast allows secure positioning to ensure that the child does not move during treatment, but considerable care is required to configure the mask for optimal airway patency while ensuring proper windows for treatments because the mask may interfere with airway access.

FIGURE 45-4 Child in fiberglass mask for radiation treatment of a cerebral neoplasm.

Radiation therapy involves “fractionated” exposure. Repeat sessions are typical. The child must be motionlessness during therapy to precisely target malignant cells. Radiation therapy is typically administered by dividing the total radiation therapy course among daily or twice-daily sessions. In general, most treatment sessions last between 15 and 30 minutes and the planning simulation session may take as long as 2 hours, depending on the nature and location of the target lesion or area for therapy. For children who require neuraxial treatments for spinal metastases, as many as four fields may be irradiated and in both the supine and prone position. Dividing the total radiation therapy course into discrete daily sessions allows normal tissue repair between sessions while the tumor burden is lessened or destroyed. These children are optimally managed via central venous access that obviates the need for repeated venipunctures. Unless there is a specific airway anomaly, daily anesthetic management typically consists of general anesthesia using a propofol infusion (with or without midazolam pretreatment),³⁹ blow-by oxygen via nasal cannula or face mask, and spontaneous ventilation monitored with ETco₂. Tachyphylaxis does not appear to be an issue even with multiple, frequent, treatments.⁴⁰ One retrospective review of 177 patients undergoing 3833 radiation treatments documented a 1.3% complication rate.⁴¹ This rate compares favorably with the rate of complications for children undergoing propofol-based anesthesia without cancer.⁴²

Dexmedetomidine sedation has been used for radiation therapy, but its use has not become widespread, most likely because of the need for a 10-minute loading dose and relatively frequent need for repeated boluses at the doses that have so far been studied.⁴³ Single-dose IV ketamine 0.5 to 0.8 mg/kg provides effective sedation, albeit with a greater half-life and more adverse effects (e.g., vomiting) than propofol.⁴⁴

One exception to the technique of moderate or deep sedation for radiation therapy is the treatment of retinoblastoma. In this case, the eye must be completely immobile during the treatment. General anesthesia or very deep propofol sedation is indicated in these cases to ensure appropriate irradiating conditions; ketamine, with its side effect of lateral nystagmus, is not appropriate in these cases.⁴⁴

The logistics of radiation therapy anesthesia or sedation are complex, even though the treatments themselves are not challenging. First and foremost, because of the large dose of radiation involved, only the child remains in the room during treatment. All monitoring must be performed via video observation. All radiation therapy units are equipped with video monitoring, but it must be adjusted to allow viewing of the physiologic monitors used for anesthesia. Children are often moved during treatment to allow different angles of access for the radiation treatment, and this must be taken into consideration when placing the monitors and the data or power cords associated with them. As with any anesthetic, positioning of the child must be considered. Many cases of spinal irradiation require the patient to be prone for treatment with the head at a specific angle with respect to the back. In addition, because of the need for the children to be in the close fitting mask during treatments, it is impossible to place an oral airway, LMA, or tracheal tube, thus the importance of monitoring expired carbon dioxide.

Most children undergoing radiation therapy are also receiving adjuvant and simultaneous chemotherapy. As the treatment progresses, nausea, vomiting, and respiratory illness stemming from local radiation effects and chemotherapy can challenge the anesthesiologist. It is important to work with the child’s oncologist to manage symptoms and complete the treatment series as close to the planned treatment regimen as possible, because this is critical to the child’s survival and maximizing quality of life.

Magnetic Resonance Imaging

MRI, magnetic resonance spectroscopy (MRS), magnetic resonance angiography (MRA), and magnetic resonance venography (MRV) are employed for the evaluation of neoplasms, nonhemorrhagic trauma, vascular lesions, cardiac lesions, orthopedic lesions (including joint disorders, osteomyelitis), central nervous system and spinal cord lesions, craniofacial disorders, detecting the origin of developmental delay, behavioral disorders, seizures, failure to thrive, apnea, cyanosis, hypotonia, and in the workup of mitochondrial and metabolic diseases.^45–48 MRA and MRV are especially helpful in evaluating vascular flow and often can replace invasive angiography in follow-up evaluations of vascular malformations, interventional therapy, or radiotherapy.^49,50 All of these imaging modalities are essentially equivalent in terms of the requirements for the provision of anesthesia or sedation and thus can be considered the same as for MRI in the following discussion.

Most MRI systems are superconducting magnets set up in a horizontal configuration within the bore so that the magnetic field is directed lengthwise to the child. The magnet is cooled by liquid nitrogen to a temperature of 39.2° F (4° C). The strength of the magnetic field in these scanners is described in tesla (T) units and range from 0.5 to 3.0 T. To put this into perspective, a 1.5-T magnet is the equivalent of 30,000 times the earth’s magnetic field.

A variety of safety issues with respect to MRI are important, as mentioned in the earlier discussion of management of acute emergencies during anesthesia outside the OR. A useful review of these issues has been published by the American College of Radiology entitled “ACR Guidance Document for Safe MR Practices: 2007.”⁵¹ All individuals who work in the MR environment should be familiar with the primary recommendations in this paper.

First and foremost is the risk of injury from ferromagnetic objects that can become attracted to the magnetic core of the MRI scanner and cause significant morbidity and mortality (Fig. 45-5). In the presence of an external magnetic field, a ferromagnetic object can develop its own intrinsic magnetic field. The attractive forces created between the intrinsic and extrinsic magnetic fields can propel the ferromagnetic object toward the MRI scanner. Numerous injuries have been reported from this mechanism. Objects that have been reported as accidentally attracted to the MRI magnet include a metal fan, pulse oximeter, shrapnel, wheelchair, cigarette lighter, stethoscope, pager, hearing aid, vacuum cleaner, calculator, hair pin, O₂ tank, prosthetic limb, pencil, insulin infusion pump, keys, watches, clipboards, and steel-toe or heeled shoes.^52,53 Mortality can result from projectile disasters, as in the case of a death in 2001 in which a ferrous O₂ tank was inadvertently brought into the MRI scanner after the wall O₂ source failed. The O₂ tank was “pulled” from the hands of the respiratory therapist and crushed the skull of the child being scanned (New York Times, July 31, 2001:B1, B5). It is absolutely essential that all portable O₂ tanks are MRI compatible and that anesthesia carts are not brought into the MRI. Many MRI scanner units now have screening protocols that include a small handheld magnet to test whether objects are ferromagnetic and thus at risk of being pulled into the magnet.

FIGURE 45-5 Magnetic resonance imaging cart that is not compatible inadvertently brought into scanner room.

The other major potential morbidity related to MRI scanning results from implanted devices (i.e., cardiac pacemakers, spinal cord stimulators, programmable ventriculoperitoneal shunts) that may malfunction in the powerful magnetic field of the MRI scanner and can cause injury. These injuries are most often caused by inappropriate patient screening or unfamiliarity with a particular implant’s MRI compatibility. Recently the U.S. Food and Drug Administration (FDA) changed the terminology for designating MRI safe objects from MRI-compatible and MRI-incompatible to MRI-safe, MRI-unsafe, and MRI-conditional (www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/GuidanceDocuments/ucm107705.htm). This terminology will not be applied retrospectively to objects previously designated as MRI-non-compatible. MRI-safe is defined as not posing any known hazard in any MR environment. MRI-conditional refers to objects that may or may not be safe, depending on the specific conditions that are present. Examples include a laryngoscope, cardiac occluder device (e.g., for closure of an atrial septal defect), halo vest, or cervical fixation device. MRI-unsafe means the object should never be brought into the MRI environment because it poses a potential or realistic risk or hazard.

All implanted objects should be carefully evaluated before a patient or health care provider enters the MRI suite. The website http://www.MRIsafety.com is a useful resource for identifying MRI-safe objects. Note that stainless steel or surgical stainless objects may interact with the external magnetic field, potentially resulting in translational (attractive) and rotational (torque) forces. Special attention should be paid to intracranial aneurysm clips (may move and potentially dislodge), vascular stents, cochlear and stapedial implants, shrapnel, intraorbital metallic bodies, and prosthetic limbs. In fact, some eye make-up and tattoos may contain metallic dyes and are at risk of causing skin, ocular, periorbital, and cutaneous irritation and burning.^54–56 Bivona (Smiths Medical, Dublin, Ohio) tracheostomy tubes pose a risk in the MRI environment because of the ferrous material within the tracheostomy tube. Bivona tracheostomy tubes are not FDA approved as MRI-compatible or MRI-safe. These tubes may produce rotational and translational motion on the tracheostomy tube itself, may create artifact on MRI images of the head or neck, and may create a thermal hazard from the heating of the ferrous elements in the magnetic environment. All Bivona tracheostomy tubes should be replaced with an MRI-safe tracheostomy tube or a tracheal tube until the FDA confirms otherwise.^57–58

Cardiac pacemaker compatibility is a matter of some debate.⁵⁹ Historically, the presence of a pacemaker has been considered a contraindication for the MRI environment. Most pacemakers have a reed relay switch that can be activated when exposed to a strong magnetic field and convert the pacemaker to the asynchronous mode. In at least two known cases, patients with pacemakers died from cardiac arrest while in the MRI scanner.⁵⁷ Adverse events associated with pacemakers in the MRI scanner include ventricular fibrillation, rapid atrial pacing, asynchronous pacing, inhibition of pacing output, and movement of the device.^58,60

Since 1996, however, changes in pacemaker electronics have included decreased ferromagnetic content and increased sophistication of the computer capabilities. In 2004, one study reported no changes in pacemaker capabilities or adverse outcomes after 56 patients with pacemakers underwent 62 MRI procedures.⁶¹ Similar results were reported in 68 patients whose pacemakers were reprogrammed to asynchronous or demand mode before undergoing scans in a 1.5-T MRI scanner. Unfortunately, there is a paucity of data on children with pacemakers or implanted defibrillators who underwent MRI scans, particularly with respect to scanners with 3-T field strength. Extreme caution and consultation with local experts is advisable before administering sedation or anesthesia in children with pacemakers in these environments.

Auditory considerations exist with respect to MRI. Specifically, a loud banging sound and vibrations are produced as the forces generated within the gradient coils of the MRI scanner cause the gradient coils to vibrate. The noises generated range from 65 to 95 dB in a 1.5-T magnet. Cases have been reported of temporary hearing loss after an MRI scan.⁶² This report suggests that earplugs may prevent the temporary hearing loss associated with MRI. Given these data, earplugs or MRI-compatible headphones are routinely used in children undergoing MRI scans.

Temperature regulation for children during sedation or analgesia for MRI has been the source of significant discussion and speculation. Cool temperatures and humidity are required for proper magnet function. These conditions are a setup for radiant and convective heat loss. Anesthesia limits intrinsic thermoregulation. On the other hand, the MRI generates radiofrequency radiation (RFR) that is absorbed by the child and may offset heat lost to the environment. The specific absorption rate (SAR) is measured in watts per kilogram and is used to follow the effects of RF heating. The FDA allows a SAR of 0.4 watts/kg averaged over the whole body.⁶³ Data suggest that children can increase their core body temperature by 0.5° C during MRI of less than 1 hour duration in a 1.5-T environment.^64,65 The temperature of infants who underwent MRI scans of the brain increased 0.2° C with a 1.5-T scanner and 0.5° C with a 3-T scanner, with minimal efforts to prevent passive heat loss.⁶⁶ Accordingly, it seems appropriate to minimize efforts to avoid passive heat loss in the MRI scanner and to monitor temperature in the 3-T environment particularly for long scans.

Focal heating remains a concern with respect to monitoring equipment in the MRI scanner. For example, the ECG leads should not have frays or exposed wires; any coils or loops in a conductor such as ECG wires or a pulse oximeter probe can cause tissue burns (Fig. 45-6). Cases of first-, second-, and third-degree burns after MRI have been reported.⁶⁷ To avoid patient injury, the following precautions should be taken: (1) Avoid creating a conductive loop between the child and a conductor (ECG monitoring or gating leads, plethysmographic gating wire, and fingertip attachment), (2) do not leave any unconnected imaging coils in the magnet during imaging, and (3) prevent all exposed wires or conductors from touching the child’s skin during the scan.

FIGURE 45-6 Burn at site of electrocardiogram pad from a frayed lead.

Many MRI scans require contrast administration. Gadolinium (gadopentetate dimeglumine) is an FDA-approved contrast agent that is intravascularly administered for MRI enhancement. Approved for use in 1998, gadolinium provides greater contrast between normal and abnormal tissue throughout the body. Gadolinium forms a complex with chelating agents that facilitates biodistribution to the extracellular compartment and excretion via the kidneys. Unlike iodinated contrast agents, gadolinium complexes do not present a significant osmotic load. Gadolinium agents are considered to be safer than iodine agents with respect to adverse reactions. It is reportedly easily removed with dialysis.⁶⁸ On the other hand, recent warnings from the FDA suggest that gadolinium-containing contrast agents may be associated with the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD) in patients with moderate to end-stage kidney disease. The FDA suggests that gadolinium be administered only if necessary in children with advanced kidney failure and that, in those children, prompt dialysis be considered after gadolinium administration for MRA studies (http://www.fda.gov/Drugs/DrugSafety/DrugSafetyNewsletter/ucm142889.htm). The incidence of severe anaphylactic reactions to gadolinium is less than that of iodine-based contrast media. The incidence of severe anaphylactic or anaphylactoid reactions is 0.01% to 0.0003%.⁶⁹ Care must be taken to ensure the proper dose by weight and creatinine if renal function is compromised. Dosing estimates may be obtained from the following website based on the glomerular filtration rate: https://www.radiologyprotocols.com (free trials available for 1 month).

MRI-compatible equipment continues to be developed and improved. Multiple MRI-compatible anesthesia machines (with ventilators), monitors (including wireless models), and infusion pumps are now available. Unfortunately the cost for this equipment is substantial. An MRI-compatible anesthesia machine costs approximately $60,000, MRI-compatible monitors range up to $140,000, and compatible infusion pumps are $12,000 to $18,000. This cost may be overwhelming, especially in facilities with limited financial resources or limited need for MRI anesthetics. However, it is highly advisable for institutions to make the investment. If patient volume is not high enough or financial backing to support such an investment is lacking, then special planning may be instituted to deliver anesthesia without a full complement of MRI-compatible equipment. Specifically, a non–MRI-compatible anesthesia machine could be used in the following manner: the machine must be positioned outside the MRI suite, and 30 feet of parallel ventilator circuit (Bain Mapleson D) or circle system extension may be threaded through the appropriate-sized hole in the console wall to the child within. Alternatively, intravenous sedation or anesthesia can be delivered using MRI-compatible infusion pumps and O₂ can be delivered using a facemask or nasal cannula. If an MRI-compatible ETco₂ monitor is not available, a conventional carbon dioxide (CO₂) monitor may be situated outside the MRI room and the 30-foot-long tubing threaded through the console wall in a similar fashion to attach to the child within.⁶⁶ If GETA is required without an MRI-compatible anesthesia machine, it is safer to anesthetize the child outside the scanner (anesthesia circuit threaded through the console wall and then back out the entrance door to an induction area), secure the airway, and then move the child into the scanner. Similarly, if propofol sedation is intended, the propofol infusion pump can also be situated outside the scanner and equipped with 30 feet of intravenous infusion tubing. It is important to determine whether the pump is able to infuse accurately through the resistance of the long tubing and that the caliber of the tubing is sufficiently large that the length of tubing required does not trigger the pump’s high-pressure alarm. An Ambu bag or Mapleson circuit must always be situated in the MRI suite and connected directly to an O₂ source within the scanner. This is critical, especially when the anesthesia machine is far from the child.

MRI-safe stethoscopes, stylets, laryngoscope, and flashlights should be available. If they are not available, standard equipment can be used with some modification and testing. The only component of the laryngoscope that is usually not MRI-safe is the battery. Replacing the standard battery with a lithium battery may be a simple, safe, and less expensive alternative to purchasing a marketed MRI-compatible and safe laryngoscope. Before introducing any equipment into the MRI environment, a rudimentary safety check should be performed by first passing a handheld magnet over the object to confirm that there is no ferrous material within. As a final safety check, an MRI safety expert should carefully introduce the object into the scanner (before bringing in a child) to confirm safety.

Anesthetic management of children in the MRI suite depends to a large extent on the availability of support personnel and equipment, the anesthesiologist’s personal anesthetic practice, and the child’s medical history. In clinical practice, the choice of anesthetic varies greatly among anesthesiologists. Airway management may include an LMA, a tracheal tube, or a natural airway (with a roll placed under the shoulders). With an LMA or tracheal tube, either inhalational or intravenous anesthesia may be used to establish a motionless child. With a natural airway, only intravenous sedation or anesthesia with propofol or dexmedetomidine is commonly used.^7,70–75 ETco₂ should be monitored; in the case of nasal prongs, a septate design that delivers O₂ (2 to 4 L/min) through one nostril while aspirating gas for CO₂ (capnometry) through the other allows for continuous assessment of respirations during spontaneous ventilation. If respiratory problems occur, immediate access to the airway is not possible while the child is in the bore of the scanner; for this reason, some anesthesiologists may prefer to insert an LMA or tracheal tube in all children. Most LMAs are MRI-compatible, although the pilot balloon should be taped to the circuit tubing when imaging the head or neck because it may create imaging artifacts (Figs. 45-7 and 45-8).

FIGURE 45-7 Laryngeal mask airway with pilot balloon left adjacent to face.

FIGURE 45-8 MRI scan of the patient in Figure 45-7 demonstrating artifact (arrow) created by ferrous material in pilot balloon.

Few studies have directly compared general anesthesia with a controlled airway to intravenous sedation or anesthesia techniques during MRI. One randomized study of 200 children demonstrated no difference in airway complications between the two groups. However, more pauses occurred during scans (for movement, etc.) with propofol sedation, but much less agitation was experienced on emergence after the scan.⁷⁶ To ensure MRI scans without interruption in the majority of children, many begin with infusion rates of propofol 200 to 250 µg/kg/min in children and either maintain that infusion rate throughout or taper the infusion rate as described previously.⁷⁷ For younger children (infants) and children with severe cognitive dysfunction, infusion rates 20% to 50% greater than 250 mg/kg/min may be required to prevent movement during MRI scans. Other studies documented agitation⁷⁸ and prolonged nausea and vomiting⁷⁹ after MRI scans performed under general anesthesia with inhalation agents. Some MRI scans (cardiac, thoracic, or abdominal) require breath holding to obtain adequate images. In such cases, it is necessary to control the airway with an LMA or endotracheal tube and deliver general anesthesia. After reviewing the literature, insufficient evidence exists to recommend a particular anesthetic technique for MRI scans. Anesthesiologists still must consider their own practice environment and expertise, the demands of the scan itself, and the comorbidities of the particular child when selecting an anesthetic technique, particularly for children undergoing a cardiac MRI.

Interventional Radiology and Invasive Angiography

Interventional radiology has evolved greatly in the last decade; many procedures that previously required operative treatment now can be accomplished with minimal intervention. In spite of the relatively little painful stimulation involved in most of these procedures, general anesthesia is often required particularly in children. Control of movement is often critical, and even the simplest procedures such as angiography often require a general anesthetic to ensure motionless conditions in children. In addition, many procedures require intermittent breath holding to acquire clear images. Furthermore, when the radiologist encounters vasospasm or needs to vasodilate arteries to enhance the images, the anesthesiologist may be requested to induce hypercarbia.

Interventions involving the abdomen and pelvis have unique considerations; N₂O can diffuse into the bowel, causing distention and, in some cases, distort or mask the vasculature of interest; it should be used with caution. In addition, when angiographic imaging of the abdomen is required, the interventional radiologist may request that the anesthesiologist administer intravenous glucagon, usually in 0.25-mg increments. Glucagon reduces peristalsis and, as a consequence, reduces motion artifact during image acquisition.⁸⁰ Glucagon has been reported to have side effects, including nausea, vomiting, hyperglycemia, depression of clotting factors, and electrolyte disturbances⁷⁰; close monitoring is warranted, particularly in neonates and small infants.

Cerebral angiograms and interventions can be complex and carry significant risk. Cerebral studies may be indicated in the workup or postoperative follow-up of vascular malformation or tumor resections, stroke, hemorrhagic events, vascular disease, and unexplained mental status changes. These interventions typically require GETA to provide hypercarbia and breath holding. Hypercarbia to ETco₂ values of 50 mm Hg or greater promote vasodilation to allow better access and visualization of cerebral vasculature (Fig. 45-9). During these cases, orogastric and nasogastric tubes, esophageal stethoscopes, and esophageal temperature probes should be used with caution because they may cause artifacts on the angiographic images.

FIGURE 45-9 Effect of hypercarbia on caliber of cerebral blood vessels; hypercarbia may assist the interventional radiologist to pass a catheter into small vessels (right).

Any child who requires a study for the potential or confirmed diagnosis of moyamoya disease should be treated with utmost precaution. These children should have an anesthetic that minimizes the risk of transient ischemic attacks and stroke during the procedure.⁷¹ Anesthetic care should begin with the preinduction administration of 10 mL/kg of intravenous fluid to minimize the risk of hypotension (and potential cerebral ischemia) on induction of anesthesia. Hypocarbia should be avoided throughout and mild hypercarbia promoted. In the event of vasospasm or difficult access of small, tortuous vessels, locally administered (through the catheter) nitroglycerin in small doses (25 to 50 µg) may facilitate visualization and access. Although often effective for discretely vasodilating specific areas, nitroglycerin will generally not have a clinically important systemic effect on blood pressure. Consequently, intraarterial blood pressure monitoring usually is not required. Specific protocols have been suggested for minimizing perioperative strokes in these children.⁷² Sedating the child before starting the intravenous line decreases crying and hyperventilation that can lead to cerebral ischemia. Close attention to postoperative pain control can similarly improve outcomes (see Chapter 24).

The anesthetic management of children with vascular malformations who present for embolization or sclerotherapy can be challenging. 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. In one review, only 18% of lesions presented before 15 years of age.⁷³ This rapid proliferative phase may occur in response to hormonal changes (pregnancy, puberty), trauma, or other stimuli. Vascular malformations may be classified as high-flow or low-flow lesions, depending on which vessels are involved. High-flow lesions may include arteriovenous fistulas, some large hemangiomas, and arteriovenous malformations. Symptoms of high-output cardiac failure predominate in the neonate, and symptoms of stroke, seizures, or hydrocephalus are more common in infants and older children.⁷³ The potential for pulmonary edema should be anticipated and assessed in the physical examination and past medical history (Fig. 45-10). 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 that is not resected may enlarge and cause further problems. It is for this reason that invasive angiography and embolization is a popular alternative to surgical resection.

FIGURE 45-10 Arteriovenous malformation of the leg with high output cardiac failure.

When embolizing vascular malformations, radiologists often strive to cut off the feeding vessels with agents such as ethanol, stainless steel coils, absorbable gelatin pledgets and powder, polyvinyl alcohol foam, glues, thread, and ethanol. The choice of agent depends on the clinical situation and the size of the blood vessel. Absolute ethanol (99.9% alcohol) is a powerful sclerosing agent that thromboses vessels even at the level of the capillary bed. It is particularly useful in the embolization of symptomatic vascular malformations. Ethanol causes thrombosis by injuring the vascular endothelium. Ethanol also denatures blood proteins. When permanent occlusion is the goal, polyvinyl alcohol foam and ethanol are often employed because they both occlude at the level of the arterioles and capillaries. Medium to small arteries may be occluded with coils, which are the equivalent of surgical ligation. In trauma situations, when only temporary (days) occlusion is the goal, absorbable gelatin pledgets or powder are employed.⁷⁴

The embolization and sclerotherapy of vascular malformations usually requires a general anesthetic to ensure motionless conditions, especially during high-risk procedures that involve injection of a contrast agent and potentially painful sclerosants. These procedures require careful planning and discussion between the interventional radiologist and the anesthesiologist for safe airway management, intraprocedural and postprocedural care, and disposition. The anesthesiologist must have a basic understanding of the procedure and the risks involved. Some of the risks are inherent to the procedure and the agents used for embolization or sclerotherapy. Pulmonary emboli have been reported after these procedures as a result of the inadvertent migration of embolization material to the lungs. The incidence of pulmonary embolization after cerebral interventions has been reported to be as great as 35% in children after embolization or coiling.⁷⁵ Before each procedure, the anesthesiologist and radiologist should discuss the radiologist’s specific requirements and concerns and decide on an anesthetic plan. Some procedures, especially embolizations of the head and neck, carry an increased risk of neurologic or cardiovascular complications.⁸¹ It is important that the anesthesiologist anticipate these potential complications and modify the anesthetic technique to permit neurologic assessment soon after extubation.

The anesthesiologist should be familiar with the mechanism of action and potential risks associated with the various agents and devices used for embolization and sclerotherapy. All sclerosants produce local hemolysis when administered into the vascular bed. Large amounts of sclerosant, particularly sodium tetradecyl and ethanol, can cause hemoglobinuria, which can result in renal injury if the child is not adequately hydrated during and after the procedure.⁸² Most children have a urine catheter placed to monitor the urine output, facilitate generous hydration, and monitor for hematuria. The anesthesiologist should generously hydrate the child with intravenous saline. On average, it has been our practice to administer as much as 50 mL/kg intravenous fluids over the course of the procedure. When hemoglobinuria is noted during the procedure, the anesthesiologist should notify the radiologist coincident with increasing the rate of fluid administration (Fig. 45-11). Hemoglobinuria may not occur until the end of the procedure, sometimes after a cumulative large dose of sclerosant has been administered or the tourniquet (if used) has been released. During procedures that involve lower extremity lesions and tourniquets, hemoglobinuria can develop soon after the tourniquet is released. Promoting diuresis with furosemide 0.5 to 1 mg/kg helps resolve gross hematuria. Occasionally, hemoglobinuria develops 1 to 2 hours after the procedure, usually while in the postanesthesia care unit. It is important to carefully balance fluid administered with urine output. In the event of persistent hemoglobinuria, sodium bicarbonate 75 mEq/L in D₅W may be administered at two times maintenance rate to alkalinize the urine and minimize precipitation of hemoglobin in the renal tubules.⁸

FIGURE 45-11 Hematuria after ethanol embolization.

Administering ethanol to sclerose a vascular malformation has the potential for severe complications.⁸³ The most infrequent but serious risk is cardiovascular collapse, which is generally preceded by hypoxemia and bradycardia. Most reported cases of cardiovascular collapse involved lower extremity malformations.⁸⁴ The cause of the cardiovascular collapse associated with ethanol is unclear, although it is reported to occur uniquely when there is direct release of ethanol into the systemic veins. Collapse can occur after release of tourniquets in extremities that have been injected with ethanol. It is critical that the radiologist communicate with the anesthesiologist whenever ethanol is being injected, as well as before the deflation of the tourniquet. It has been recommended that any child at significant risk of systemic ethanol egress should have a pulmonary artery catheter placed before the procedure to identify changes in pulmonary artery pressure that might herald electromechanical dissociation. Significant increases in pulmonary artery pressure resulting from pulmonary vasoconstriction necessitate interrupting the administration of ethanol until the pressure normalizes. Significant fluctuations in vital signs include an increase in pulmonary artery pressure, a decrease in systemic blood pressure, decrease in ETco₂, or O₂ saturation, cardiac arrhythmias, or full cardiac arrest.

Ethanol can produce a state of intoxication. The ethanol used for embolization and sclerotherapy is 95% to 98% pure. Children who receive greater than 0.75 mL/kg can become clinically intoxicated. Blood levels correlate with the volume of ethanol administered, regardless of the location or type of vascular malformation (Fig. 45-12). On extubation, these children display either significant agitation or excessive sedation and analgesia; opioids should be administered with caution because they have a synergistic effect with ethanol and potentially cause unwanted respiratory depression. It is generally advisable to administer minimal or no opioids until the child is extubated and confirms the presence of pain. Ketorolac may be administered intravenously after soliciting the agreement of the radiologist, removing the invasive catheters, and ensuring hemostasis has been achieved.

FIGURE 45-12 Positive relationship between serum ethanol level and amount of ethanol administered.

(From Mason KP, Michna E, Zurakowski D, Koka BV, Burrows PE. Serum ethanol levels in children and adults after ethanol embolization or sclerotherapy for vascular anomalies. Radiology 2000;217:127-32.)

Children with vascular malformations, especially venous malformations, can have preexisting coagulation disturbances that resemble disseminated intravascular coagulation.⁸⁵ Children with laboratory indices consistent with preexisting consumptive coagulopathy should have a hematology consultation and, if possible, receive heparin for 2 weeks before the procedure to replenish their fibrinogen levels. The anesthesiologist may be asked to administer cryoprecipitate or platelets during the procedure to promote clotting and successful sclerosis. The use of ethanol for sclerosis or embolization can also elicit a coagulation disturbance that resembles disseminated intravascular coagulation. There is a statistical relationship between the amount of ethanol administered and the degree of coagulation disturbance elicited.⁸⁶ Additional cryoprecipitate or fresh frozen plasma transfusions are given only in severe cases, because the coagulopathy is generally not symptomatic and resolves within 5 days. However, major surgery should be deferred until the coagulation parameters have normalized.

It is important to be aware of the potential morbidity associated with embolization procedures. Type and crossmatch should be performed for all children scheduled for embolization in anticipation of possible major hemorrhage. Embolization therapy has been associated with multiple potentially devastating outcomes, including stroke, cerebral abscess, bleeding, cyanosis, and pulmonary embolism.⁸⁷ Postprocedural mortality is reported to be 5% to 6%.⁸⁸ It is important to document full return of neurologic status after the child recovers and the trachea is extubated. Vascular malformations involving the airway are particularly challenging (Fig. 45-13). The anesthesiologist and radiologist should review the imaging studies (usually MRI) before the procedure. The scans should be evaluated for patency of the nares, nasopharynx, hypopharynx, and oropharynx, as well as for an uncompromised trachea, carina, and bronchi. MRI will also confirm that there is no malformation in the nares or nasopharynx, which could be damaged or bleed during intubation. Most interventional radiology suites are not situated in the OR. If there is any potential for airway compromise, difficulty in attaining a mask airway, or failure to intubate, the airway should be secured in the OR before transport to the radiology suite. In general, an otolaryngologist or another specialist skilled in bronchoscopy and tracheotomy should be present in the OR prepared to perform bronchoscopy (fiberoptic or rigid) or tracheostomy should the airway be lost.

FIGURE 45-13 Venous malformation of the face with patient sitting upright (A) and supine (B).

If postsclerotherapy edema and vascular congestion involving the airway structures are anticipated, the child’s trachea should be intubated nasally and remain intubated for 48 hours or until the swelling subsides. Nasal intubation is preferred to minimize the risk of dislodging the tracheal tube or premature extubation. The decision to have the child remain intubated postoperatively is usually made before the start of the procedure, after the anesthesiologist and radiologist review the MR images together. If the trachea remains intubated postoperatively, the trachea is extubated in the intensive care unit after the presence of an air leak around the tracheal tube is confirmed or a flexible nasal fiberoptic view of the airway can be performed at the bedside. If there is any doubt about the patency or self-sufficiency of the airway, these children should be transferred to the OR for tracheal extubation in a controlled setting with an otolaryngologist present.

Venous malformations involving the head, neck, or airway structures typically swell with dependency or Valsalva maneuver (e.g., crying). Before extubating the trachea, these children should be positioned head-up to promote venous drainage and reduce swelling. Efforts should be made to minimize coughing before tracheal extubation. In the event of respiratory compromise, venous malformations can enlarge when the child coughs, increases intrathoracic pressure, or uses accessory muscles. Attempts at reintubation, cricoid pressure, head extension, and mask ventilation can further enlarge the malformation. Mask ventilation can be challenging, sometimes impossible, if the malformation is swollen and firm. Achieving an occlusive mask seal is particularly difficult when there is swelling of the cheek, tongue, lip, chin, or nares. Venous malformations of the lips and tongue, because of their blue color, can make it difficult to assess the child for hypoxemia in the event of respiratory distress. Reintubation can become impossible in these situations because all of the maneuvers to achieve a mask seal increase venous pressure and swelling. When attempting to reintubate the trachea of a child with intraoral or pharyngeal malformations, special care should be taken to avoid damaging the malformation: even a small nick can create significant bleeding. In the event of oropharyngeal bleeding and inability to mask ventilate and/or intubate, it is critical to have alternative airway devices immediately available. LMAs in particular can be lifesaving. Proper insertion and inflation of the LMA can secure an airway and, more importantly, tamponade bleeding. However, because the LMA rests above the vocal cords, it does not protect the airway from pulmonary aspiration.

Intravascular Contrast Media

The use of intravascular contrast media is ubiquitous in interventional radiology and cardiac catheterization. It is important that the anesthesiologist be aware of the risks and potential side effects of these agents. Almost all life-threatening reactions occur immediately or within 20 minutes of contrast agent administration. Low-osmolality ionic and nonionic contrast media are associated with a reduced incidence of adverse events, especially non–life-threatening events compared with high-osmolality contrast media. Serious contrast reactions are estimated at 1 to 2 per 1000 studies using high-osmolality contrast media versus 1 to 2 per 10,000 studies with low osmolality contrast media.^89,90 Adverse reactions include nausea, vomiting, hypotension, urticaria, bronchospasm, anxiety, chills, fever, facial flushing, seizures, pulmonary edema, and cardiovascular collapse. Anaphylactic shock is the most worrisome of all contrast reactions and may occur as early as 1 minute and as late as several hours after administration of the contrast material. Although adverse reactions to intravascular contrast media are unpredictable, some risk factors are identifiable. These include children who suffer from allergies or an atopic disease, children with asthma, significant cardiovascular disease, and paraproteinemia, and children with prior contrast reactions have an increased incidence of adverse reactions.⁹¹ Children who have been identified as being at increased risk of a contrast reaction should be premedicated with corticosteroids and antihistamines. The American College of Radiology suggests that corticosteroid premedication, along with low osmolality contrast media, should be used for those at risk.^91,92

Because the contrast agent is hypertonic relative to plasma, attention needs to be paid to the risk of a triphasic response: initial but transient (30 to 60 seconds) hypotension, followed by hypertension as the contrast material draws fluid intravascularly, 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. For this reason, special attention should be paid when administering iodine contrast to any child with a history of congestive heart failure. The initial increase in blood volume may precipitate cardiovascular compromise. Renal failure from contrast media can occur with high- and low-osmolality contrast media. Although the cause of the acute renal failure is not known, risk factors include preexisting renal insufficiency (serum creatine 1.5 mg/dL or greater), diabetes mellitus, dehydration, cardiovascular disease, hypertension, and hyperuricemia. For these at-risk children, good hydration must be maintained, along with careful follow-up of renal function.⁹³ It should be noted that those with paraproteinemias (multiple myeloma, Waldenström macroglobulinemia) are predisposed to irreversible renal failure from protein precipitation in renal tubules, which is preventable with proper hydration.⁹⁴

Endoscopic Procedures

Gastrointestinal endoscopy is a common procedure for pediatric gastroenterologists. Both upper and lower endoscopies involve significant stimulation, which requires deep sedation or general anesthesia in infants and children. A range of sedation and anesthesia options may be used for both simple^95,96 and more complex procedures such as foreign body removal, endoscopic retrograde cholangiopancreatography (ERCP), and percutaneous endoscopic gastrostomy (PEG) placement.⁹⁷ The choice of deep sedation versus general anesthesia (with or without a tracheal tube) depends on the medical condition of the child, the risks associated with the specific procedure, and the anticipated duration. Upper esophagogastroduodenoscopy (EGD) in infants (less than 10 kg) generally requires tracheal intubation to avoid airway compression caused by the endoscope pressing the trachealis muscle into the trachea. However, few definitive data exist on this issue (few studies include infants less than 1 year of age). At Dartmouth Hitchcock Medical Center, we have found that if the endoscopist is willing to use the smallest available pediatric scopes, successful sedation or anesthesia without a tracheal tube is possible for infants as small as 6 to 7 kg. In some cases an LMA may be used to secure the airway and the cuff deflated to allow passage of the endoscope and then reinflated once the scope has entered the esophagus. It is advised to hold on to either a tracheal tube or an LMA during the procedure to reduce the risk of the endoscopist dislodging it during their manipulations.

Many techniques may be employed successfully to maintain adequate conditions for upper and lower gastrointestinal endoscopy. Although all anesthesia-delivery areas must meet ASA standards, scavenging and ventilation in endoscopy suites may not always be effective in allowing the safe use of inhalational anesthetics. In these cases, total intravenous anesthesia can substitute for potent inhalation agents.^98–100 Over the last several years, various combinations of intravenous agents have been described for the delivery of sedation and anesthesia in the endoscopy suite for children. As a general rule, propofol is used either alone,¹⁰¹ in combination with an opioid (fentanyl or remifentanil),^102,103 or with ketamine.¹⁰⁴ Outcomes after deep sedation or anesthesia with propofol and inhalational anesthesia were similar.⁹⁹ However, the time to awakening was more rapid after the inhalational anesthetic, the incidence of agitation on emergence was less, and the time to hospital discharge earlier after propofol.

Access to the airway is obviously limited once a transoral endoscope is in place. The two most stimulating portions of the esophagogastroduodenoscopy are transoral and transpyloric passage of the endoscope. After endoscope insertion, the sedation or anesthesia can often be reduced without adverse effect on the procedure conditions. Smooth insertion of the endoscope can be aided by topical spray of local anesthesia to the oropharynx to reduce the discomfort of passing the endoscope and to prevent coughing and gagging. For older children, topicalization of the oropharynx can be accomplished before sedation and the child can position himself or herself for the gastroenterologist (lateral position). Sedation can be subsequently accomplished with the child prepositioned. For cases performed without tracheal intubation, a CO₂ sampling nasal cannula can be placed and used over the nose or near the mouth (for those who do not breath through the nose) to supplement O₂ and allow a monitor of respiration.

Upper endoscopies have the inherent risk of apnea, laryngospasm, bronchospasm, and airway obstruction. Most problems resolve after withdrawal of the endoscope and positive-pressure ventilation with a face mask.¹⁰⁵ In rare situations, tracheal intubation may be required to complete the procedure or resolve an airway issue. In young infants, abdominal distention secondary to air introduced into the stomach may impair diaphragmatic excursion, leading to hypoventilation. Little published evidence exists on which to base age-related practice in endoscopy sedation and analgesia, experience led several groups to select all infants up to 6 months of age as the age interval for which general anesthesia with tracheal intubation is required, because of a greater frequency of respiratory complications.^95,96 When extubating the tracheas in these infants, be wary that residual air in the stomach can impair effective ventilation and contribute to desaturation or O₂ dependence in the recovery room. Thus it is important to remind the endoscopist to suction any residual air from the stomach before removing the endoscope.

Few large studies have reported outcomes after pediatric gastrointestinal endoscopy. The Clinical Outcomes Research Initiative (CORI) is a national registry of endoscopic procedures that was started in 1995. The PEDS-CORI is the pediatric component that was started in 1999. A 2007 report collected the complications from pediatric upper endoscopy involving 10,236 encounters from 13 different institutions over 4 years.¹⁰⁶ Overall, there was a 2.3% incidence of complications (of any kind). Of these, 79.9% were cardiopulmonary, 18% were gastrointestinal complications, and 5.9% were other complications, including prolonged sedation, drug reactions, or rash. Not surprisingly, children who developed complications were younger and had a greater ASA physical status. General anesthesia was associated with a reduced overall complication rate (1.2%) compared with that in the IV sedation group (3.7%). Although these data were not controlled or randomized, it does shed some insight into the complication rates associated with pediatric sedation outside the OR.