Children commonly require sedation to complete radiologic studies and procedures successfully. Without sedation, many young children are unable to remain motionless even for nonpainful imaging studies, such as bone scans or magnetic resonance imaging (MRI). In addition, patients may require analgesia and anxiolysis for painful interventional radiologic procedures. In many cases, the radiologic study or procedure itself poses only minimal risk to the patient, but the administration of sedation adds the most significant incremental risk. In this article, we discuss important aspects of pediatric sedation for different radiologic procedures.
RADIOLOGY SEDATION PROGRAMS
The recognition of the risks inherent in procedural sedation has prompted several regulatory and professional organizations to formulate safety guidelines. The Joint Commission on Accreditation of Health Care Organizations (JCAHO)1 requires each institution to establish a uniform standard of care for pediatric sedation but gives only general guidelines for its content. The American Society of Anesthesiologists (ASA),2 the American Academy of Pediatrics (AAP),3 and the American College of Radiology (ACR)4 provide additional practice standards, but these also leave much room for variability. As a result, institutions nationally employ many different care models for radiology sedation.
Historically, radiologists5 frequently were the physicians responsible for most radiology sedation care, at least for relatively healthy children. Pediatric anesthesiologists typically provide care for children who are critically ill or have more complex sedation needs, although they provide all radiology sedation in some settings. In other settings, pediatric critical care or emergency physicians primarily are responsible for radiology sedation. Regardless of the training of the responsible physician, all radiology sedation should comply with the relevant practice standards, including the ASA practice guidelines for nonanesthesiologists.
The overriding consideration of these guidelines is that sedation is a continuum, ranging from anxiolysis through moderate and deep sedation, to general anesthesia. Idiosyncratic patient responses to medication can result in a deeper level of sedation than intended, and the sedation provider must be able to rescue patients from a deeper-than-intended state of unconsciousness. Minimum requirements for sedation providers include pediatric advanced life support (PALS), and advanced cardiac life support (ACLS) if adults are to be sedated, often supplemented by other institution-specific standards. The ideal training for airway rescue and management has not been universally standardized.
In recent years, several institutions have begun building dedicated, nonanesthesiologist-staffed sedation services to complement the care provided by anesthesiologists. These services are designed to bring a uniform level of safe sedation care to radiology patients, while reducing overuse of scarce pediatric anesthesiology resources.
At The Children's Hospital of Philadelphia, a team of specially trained and privileged pediatric hospitalists manages the majority of sedations for radiology imaging. Privileging requirements for these physicians include PALS and ACLS certification, completion of didactic training (including a written examination), and 10 days in the operating room, working side-by-side with pediatric anesthesiologists and learning principles of cardiopulmonary monitoring and anesthetic pharmacology. The hospitalists gain familiarity with preoperative evaluation, recognition of patients who may prove difficult to ventilate or intubate, and intraoperative airway management techniques. Bag-mask ventilation techniques are emphasized, as are early recognition and management of complications such as hypoventilation, airway obstruction, and laryngospasm. The hospitalists are required to demonstrate competency in rescuing a patient with compromised respiration and to document successful completion of specified numbers of mask ventilations and endotracheal intubations.
PREPROCEDU RAL EVALUATION FOR RADIOLOGIC SEDATION
Practice guidelines mandate that a thorough patient assessment be performed prior to sedation. This includes, at minimum, a history and focused physical exam. A thorough evaluation of the airway is especially critical, with a focus on anatomical issues that could complicate airway rescue in the event of central or obstructive apnea.6
Figure 1. Anxiolysis algorithm guideline.
The examination should evaluate the patient's range of neck motion as well as the size of the mandible and tongue. Clinical experience with children who proved to be difficult to ventilate has shown that obstructive sleep apnea and craniofacial abnormalities7 are important predisposing factors. Many of these patients should be referred to the department of anesthesiology for further management. Children with significant cardiac disease require a pre-sedation evaluation by a pediatric cardiologist.
During the pre-sedation evaluation, the sedation provider should elicit a list of current medications and allergies and confirm adherence to the institution's standard fasting guidelines. A history of sedation or anesthesia often helps anticipate any problems. In addition, it is helpful to evaluate the patient using the ASA physical status classification (Cote, Table 2, see page 628). Class I or II patients often are good candidates for sedation by a nonanesthesiologist, Class UI patients may require further scrutiny or an anesthesiology consultation, and Class IV and V patients should be managed exclusively by anesthesiologists.
Figure 2. Primary sedation algorithm guidelines for children older than 1.
The AAP, ASA, and ACR guidelines all provide minimum standards for personnel and available facilities during pediatric sedation. A skilled medical professional not involved in performing the procedure should be responsible for monitoring the patient. Appropriately sized airway equipment, oxygen, and suction need to be readily available, as should emergency and rescue medications. Continuous pulse oximetry and heart rate monitoring are mandatory, and respiratory rate and blood pressure should be checked at regular intervals (at least every 5 minutes). Capnography should be considered for all patients, especially in radiology settings where direct observation of respiratory effort may not be feasible.
Magnetic Resonance Imaging (MRI)
MRI is superior to computerized tomography (CT) for demonstrating central nervous system lesions and eliminates the risk of exposure to ionizing radiation. Many infants require MRI to help establish the cause of sacral dimples, central apnea, or new seizure activity. Older children may require MRI in the course of establishing a diagnosis for developmental delay, persistent headaches, or scoliosis. Oncology patients frequently require serial MRI studies over many months.
The goal of sedation for MRI is the absence of patient movement, to eliminate motion artifact. Therefore, a hypnotic agent is required. Figures 1 through 3 display the sedation algorithms for radiology imaging used at The Children's Hospital of Philadelphia. Analgesics (ie, opioids) and anxiolytics (ie, benzodiazepines) are not indicated except in small doses to improve the efficacy of the hypnotic agent. In infants, orally administered chloral hydrate is the most commonly used hypnotic agent. Older children may receive IV pentobarbital. Propofol is an appealing agent for MRI sedation, but most institutions limit its use to anesthesiologists because of its potency and the risk for cardiorespiratory depression.
The confined space inside a closed MRI scanner and the noise of the magnet can be disturbing to older children and teenagers who are otherwise able to lie still. These children may be managed with anxiolysis by administering an IV or oral dose of a benzodiazepine (eg, midazolam or diazepam). Analgesia is a critical element to consider in the management of a child who will not be fully sedated. For example, a teenager who had recent spinal surgery and needs to He still on her back for 2 hours may complete the study with morphine or fentanyl.
The most significant practical challenge in the MRI environment is the powerful magnetic field that is present whether or not a scan is in progress. This precludes the use of metallic devices in the area near the scanner, including infusion pumps and monitoring equipment. The American College of Radiology White Paper on MR Safety8,9 provides specific guidance to MRI facilities on developing safety standards and protocols. Every MRI sedation provider should be familiar with both this document and internal institutional policies regarding MRI safety. Ferromagnetic objects become dangerous projectiles in the presence of the scanner's powerful magnetic field, resulting in injuries to patients and staff. Sedation providers should ensure that oxygen tanks in the facility are made of aluminum and that no MRI-incompatible equipment, including gurneys, YV poles, and stethoscopes, is brought into the scanner room.
Figure 3. Primary sedation algorithm guidelines for children younger than 1.
The unique requirements of the MRI environment result in sedation care that is delivered from a distance. Patient monitoring during a sedated MRI should include all usual parameters (eg, blood pressure, electrocardiograph, pulse oximetry), with displays in the scanner control room. Direct visual evaluation of the patient's respiratory effort usually is limited in the MRI setting because of the distance between the patient and the observer. Continuous monitoring of the end-tidal carbon dioxide level can provide an earlier warning of respiratory changes than the oxygen saturation or heart rate. Capnography can be accomplished through a specially designed nasal cannula that allows for side-stream measurement of carbon dioxide levels. Capnography also is helpful in the early detection of upper airway obstruction, as the tracing provides both end-tidal carbon dioxide levels and a respiratory rate. Intermittent airway obstruction and associated head rocking cause motion artifact on MRI scans. Providing a patent airway through the insertion of a nasal (or oral) airway usually relieves this motion.
The basic objective of sedation in CT is similar to MRI: to provide hypnosis to children too young to remain immobile. However, improvements in CT scan technology have reduced the need for sedation.10 Multisection helical CT is significantly faster than traditional CT, and many children are able to lie still during these brief scans.
Young or anxious children do require sedation, especially for longer studies. The CT environment poses fewer challenges than MRI. Standard monitoring equipment can be used in the scanner room and the design of modern CT scanners allows for good visualization of the patient's respiratory effort during the scan. If necessary, the sedation provider can wear lead protection against radiation and stay in the room with the child.
The medications used for accomplishing sedation for CT are similar to those for MRI. However, the effects of chloral hydrate and pentobarbital usually outlast the duration of the CT scan by a considerable amount of time.
An issue that has raised considerable interest in recent literature is the timing of oral contrast (eg, diatrizoate meglumine, gastrografin) for sedated abdominal CT scans. Radiologists prefer that oral contrast be administered within an hour before the scan. However, because of its high osmolality, pulmonary aspiration of oral contrast would cause a toxic pneumonitis. While it would be reasonable to consider this a clear liquid for the purposes of gastric emptying, administration within 1 hour of sedation violates generally accepted fasting guidelines.
There is no uniform practice concerning this issue. Many institutions routinely sedate children with pentobarbital or chloral hydrate after administration of oral contrast.11,12 However, the available studies suffer from small sample sizes relative to the probable incidence of the most serious adverse events. Therefore, when asked to provide anesthesia in this situation, many anesthesiologists routinely intubate the trachea to protect the airway. At The Children's Hospital of Philadelphia, we do provide mild to moderate sedation without a protected airway for children who have received oral contrast for CT, and we modify our medication plan to achieve the least possible level of unconsciousness.
Other Radiologic Studies
Nuclear medicine studies (eg, bone scan) also require prolonged immobility and may necessitate the administration of an hypnotic agent. In addition, performance of a barium enema in an older child, especially one with developmental delays, may require some form of sedation.
One particularly challenging procedure is the voiding cystourethrogram (VCUG), a routinely requested study in children with urinary tract infections or hydronephrosis. The required urethral catheterization is usually painful, especially in an anxious child who is not sufficiently relaxed to allow for easy passage of the catheter. However, children cannot be rendered unconscious for the procedure because they need to be able to void. Many institutions have found that a dose of oral midazolam 30 minutes before the study provides excellent anxiolysis and amnesia.13 At The Children's Hospital of Philadelphia, childlife professionals provide a crucial additional dimension by preparing the child and providing emotional support during the procedure.
The past decade has witnessed a dramatic increase in the number and scope of procedures performed by interventional radiologists (IR). Common reasons for referral to IR include insertion of central venous access catheters, placement of gastrostomy tubes, abscess drainage, and biopsies of various intracavitary masses. Interventional radiologists also may perform biliary stenting and osteoid osteoma removal. Most of these procedures require some form of sedation or general anesthesia.
Sedation considerations for IR procedures are different from those for imaging studies because of the need for analgesia and anxiolysis in addition to immobility. Therefore, sedation for many IR procedures aims to achieve multiple goals. Hypnosis and lack of patient motion may be achieved by administering oral chloral hydrate to young infants or rV pentobarbital to older children. Fentanyl or midazolam are common choices for analgesia or anxiolysis, respectively. The need for systemic analgesia often can be reduced by the administration of local anesthesia. As a cautionary note, combining multiple sedating medications increases the risk of synergistic effects, resulting in respiratory depression and upper airway obstruction.
Ketamine has been suggested as an ideal agent for IR procedures.14 After intravenous or intramuscular injection, patients rapidly enter a dissociative state in which they experience profound analgesia, amnesia, and sedation. Ketamine typically induces mud tachycardia and hypertension, and respiratory effort usually is well maintained. The most important potential adverse effects include laryngospasm, emergence agitation, and delayed psychotropic effects, such as hallucinations and nightmares. While the agent has a good track record in pediatric procedural sedation, many institutions restrict the use of ketamine to anesthesiologists and emergency room physicians.
Many different practice models for radiology sedation can provide satisfactory patient care. Adherence to recognized safety standards and the training and experience of sedation providers are critical for a successful program. Pediatricians should develop an appreciation of safe practices in the radiologic environment and the requirements related to individual studies and procedures.
Sedation needs in radiology are diverse. Imaging procedures such as MRI, CT, and nuclear medicine studies require hypnosis to achieve results without motion artifact. Invasive studies may require the use of analgesic and anxiolytic agents. IR procedures often require the use of multiple agents.
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