Anesthesia for magnetic resonance imaging and computed tomography procedures

INTRODUCTION — Anesthetic management of patients undergoing magnetic resonance imaging (MRI), or computed tomography (CT) procedures poses unique risks and challenges due to the scanning equipment itself, communication difficulties, and an off-site location that is typically distant from the main operating room. In the CT suite, radiation exposure poses an additional hazard. In the MRI suite, the anesthesiologist must manage unique hazards due to the strong magnetic field, radiofrequency energy, and loud acoustic noise, as well as use specialized MRI safe equipment for anesthetic delivery and monitoring.

This topic will review anesthetic management of adults and children undergoing MRI or CT procedures. The principles and risks of MRI and CT imaging in adults and children are addressed in other topics:

●(See "Principles of magnetic resonance imaging".)

●(See "Radiation-related risks of imaging".)

ANESTHETIC CHALLENGES FOR MAGNETIC RESONANCE IMAGING

Physical location of the MRI suite — Preparation for anesthetic care in an MRI suite poses unique challenges and requires extra time compared with preparations in a standard operating room (OR). The MRI suite is typically remote from the main OR location, which poses general challenges for anesthetic management, including transport of some monitors and pharmacologic agents [1-6]. Details are discussed in a separate topic. (See "Considerations for non-operating room anesthesia (NORA)", section on 'Anesthetic challenges in non-operating room locations'.)

Communication in the MRI suite — Communication challenges and distractions include [3,5,6]:

●Darkened room

●Distance to the patient

●Obstructed line of sight to the patient and monitors

●Loud acoustic noise generated during fast pulse MRI scanning, which may obscure alarms on monitors and other anesthesia equipment. Also, the hearing protectors worn by medical team members in the MRI suite impair communication. (See 'Anesthetic challenges for magnetic resonance imaging' above.)

●Presence of multidisciplinary team, some of whom may not work together with regularity. For this reason, members of the care team (eg, radiologists, anesthesiologists, scanning equipment technicians, subspecialized nursing personnel) should discuss the sequence of events that will occur in a pre-procedure briefing [3,5,6]. Issues include how and where anesthesia will be induced (eg, in the imaging room itself or in a separate induction room), how the patient will be transported to the imaging room and positioned, specific requirements for the imaging procedure (eg, periods of apnea for cardiac imaging), procedures for possible emergencies, and where the patient will recover from anesthesia. Additional goals for the briefing include verification of availability and proper functioning of all necessary anesthetic and monitoring equipment. (See "Patient safety in the operating room", section on 'Timeouts and briefing in the operating room'.)

Environmental risks and challenges — Anesthetic management of adults or children undergoing MRI procedures poses unique risks for both patients and anesthesia care providers [4-6]. MRI uses a strong magnetic field to orient atoms to the field's north-to-south poles, and then uses radiofrequency pulses to change the orientation of the nuclei of specific atoms. As the nuclei return to their ground state, they radiate radiofrequency energy, which is then analyzed to create the image. The strong magnetic field, radiofrequency pulses with associated electromagnetic interference (EMI), and loud acoustic noise are potentially hazardous [3-5]. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Patient safety concerns'.)

Magnetic field — The strong static magnetic field may cause even heavy objects (eg, oxygen or nitrous oxide tanks) to become accidental projectiles into the bore of the scanner [4,5,7]. This magnetic field is constantly present, even when a patient is not being actively scanned. Thus, the anesthesia gas machine, monitors, intravenous (IV) infusion pumps, and all other anesthetic equipment must be MRI safe. The outermost line on the floor of an MRI suite is the 5 Gauss line. This is the point at which pacemakers, implantable cardiac defibrillators, and other medical devices may be affected by the magnetic field. The field strength increases rapidly as one gets closer to the magnet. Stretchers, intensive care unit (ICU) beds, and crash carts used for advanced cardiac life support (ACLS) are not MRI compatible [3]. (See 'Equipment' below and "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Safety zones'.)

Some anesthesiologists will not be able to safely enter the MRI suite. For example, those with a pacemaker (PM), implantable cardioverter-defibrillator (ICD), or implanted insulin pump cannot provide anesthetic care in this setting. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Assessing implants, devices, or foreign bodies for MRI'.)

When possible, the anesthesiologist should remain at least 0.5 to 1 m from the bore of the scanner and should move slowly when it is necessary to be near the bore. Movement of a mannequin head faster than 1 m/second induced electric fields/current densities above recommended levels [8]. Rapid patient motion in the strong magnetic field near the MRI scanner produces an electrical current within the body, which may cause symptoms such as nausea, vertigo, headache, light flashes, loss of proprioception, or a metallic taste. The anesthesiologist may experience similar symptoms (typically dizziness or headaches) with rapid head movement in or near the magnet bore [4].

Radiofrequency energy — Radiofrequency energy can cause tissue or device heating and can also induce current in conductors such as (ECG) leads, equipment cables, or fluid-filled tubing [5]. Skin or other tissue burns can occur [3,5], or in rare cases, a fire [9]. Therefore, MRI compatible ECG leads are used, and equipment cables and IV tubing are not positioned directly on the patient's skin. (See "Fire safety in the operating room", section on 'Fire on the patient'.)

Electromagnetic interference — The strong magnetic field and radiofrequency energy may cause artifacts that limit clinical interpretation of the electrocardiogram (ECG) or pressure waveforms [6].

●Electrocardiogram (ECG) – The magnetic field can produce artifactual changes in the ECG waveform. To eliminate the use of long conductors, MR-safe monitors use either wireless transmitters or fiberoptic cables for the ECG and pulse oximeter, with communication to a central monitoring station that sends the waveforms to a remote display unit. However, the ECG waveform may be affected by interference from several sources. For example, when the patient's upper body is in the scanner, the ECG is subject to interference from a phenomenon called hydromagnetics, whereby the strong magnetic field produces a current in blood as it flows through the ascending aorta and aortic arch. This results in artifactual alterations of the ST segment of the ECG. Although most monitors designed for use in the MRI suite incorporate one or more preprogrammed filters to improve the waveform, residual artifacts may persist.

Also, during periods of pulsating radiofrequency energy, the magnetic field may generate electromagnetic interference (EMI) that affects the entire waveform of the ECG. Thus, clinical interpretation of the ECG may be difficult while the patient is in the scanner, despite availability of ECG leads that are shielded to mitigate this effect as much as possible.

●Pressure waveforms – Other standard monitor features such as waveform filters that are typically helpful for optimizing arterial or other pressure waveform analysis may be absent or inadequate in MRI safe/compatible monitor models.

Loud acoustic noise — Loud acoustic noise is generated during the pulses of energy required for imaging because the gradient coils vibrate loudly in the strong magnetic field (figure 1) [4,5]. Although a sound level of 40 decibels (dB) is generally an acceptable limit in an operating room, an MRI scanner can generate noise levels as high as 125 dB (approximately as loud as a chainsaw) during fast pulsed imaging sequences, especially with stronger static fields.

Since this noise may cause hearing damage, earplugs should be inserted into the patient's ears. Medical personnel can also experience hearing loss due to the loud acoustic noise. Hearing protectors should be worn by the anesthesiologist if he or she is in the room while the patient is being scanned. These should attenuate the noise level by up to 10 to 60 dB, which may also impair the ability to hear alarms on monitoring and other equipment and may make communication with other medical personnel difficult.

Emergency quench — A rare occurrence is an unexpected magnet quench (defined as loss of magnet superconductivity with sudden boil-off of cryogenic [-269°C] liquid helium), or a controlled quench performed to remove the patient from the bore [4,5]. The magnet is only deliberately quenched in the event of a truly life-threatening emergency, such as a patient or staff member being pinned against the scanner by a ferromagnetic object. (In most cases, if a magnetic object is stuck to the scanner but nobody is in danger, the magnet is ramped down slowly without being quenched and the piece of equipment is removed.) In the event of a quench, the quench duct should carry the helium out of the building in which the MRI is installed. If not properly vented, the large quantity of gaseous helium released during a quench can result in rapid, complete displacement of air inside the MRI suite, possibly causing hypoxia in the patient and MRI personnel [4,5]. Although the patient and all staff are evacuated from the scanner room as quickly as possible during a quench, entrance or exit from the suite may not be possible for several seconds due to high pressure against the doors that is generated by the escaping gases.

Preparation: Special considerations for MRI procedures

Equipment — MRI-compatible monitors may be unfamiliar and significantly different from typical operating room (OR) monitors. Available MRI safe/conditional monitors, gas machines, and IV infusion pumps are typically used only in MRI suites and may be unfamiliar to anesthesia personnel who do not work in these areas often [5,6]. Preparation should include a review of the user manual for unfamiliar equipment. The anesthesiologist should also verify that the monitor used in the MRI suite offers the necessary capabilities for safe patient care (eg, the ability to monitor invasive blood pressure in a critically ill patient).

Anesthesia technicians (assistants who transport and restock all equipment and supplies) should be available during preparation of equipment as well as during the scanning procedure. All assistants working in the MRI suite should receive specialized training in patient and personal safety in this environment, as well as the types of special equipment and supplies that may be needed [3-6]. (See 'Environmental risks and challenges' above.)

Monitoring equipment is classified as "MR safe," "MR unsafe," or "MR conditional" [3-5]. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Assessing implants, devices, or foreign bodies for MRI'.)

●MR safe – MR safe equipment poses no known hazards in any MRI environment. Magnetic field and radiofrequency energy produced by the scanner can cause heating in the conductive components of these monitors, placing the patient at risk for burns or fire [9]. Thus, MRI safe equipment (eg, ECG leads, pulse oximeter probes, blood pressure cuffs and cables) should be used. Also, wires, equipment cables, and oxygen or intravenous tubing are padded, and placement directly on the patient's skin is avoided. (See "Fire safety in the operating room", section on 'Fire on the patient'.)

●MR conditional – MR conditional equipment poses no known hazard in a specified MR imaging environment with specified conditions of use. For example, some anesthesia machines such as the General Electric Aestiva 5 anesthesia machine may be used in field strengths of up to 300 Gauss; the Dräger Fabius MRI machine may be used in field strengths of up to 400 Gauss; while the BleaseGenius MRI machine may be used up to the 1000-Gauss line. Equipment labels denote the conditions (eg, maximum strength of the magnetic field, spatial gradient, time rate of change of the magnetic field [dB/dt], radiofrequency [RF] fields) under which the equipment was tested.

●MR unsafe – MR unsafe items are known to pose hazards in all MR environments. For example, cardiac defibrillators and standard gas cylinders (eg, oxygen, air, nitrous oxide) may become large dangerous projectiles flying unexpectedly into the bore. Even if secured in place, some types of equipment are damaged by proximity to the extremely strong magnetic field. Even if an oxygen tank is MR safe or conditional, the carrier in which it is transported may be ferromagnetic. All gas delivery equipment should be tested or verified to be safe before being brought into zone IV. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Safety zones'.)

Preparation for MRI procedures includes ensuring that all monitors, equipment, and the anesthesia machine itself are MRI safe/compatible [3-6]. If the patient's airway is to be managed near the scanner, it is also necessary to use MRI-safe/compatible laryngoscope handles, blades, stylets, and stethoscopes.

In institutions without MRI-safe/conditional pumps infusion pumps for administration of IV agents to maintain general anesthesia, specially designed lengths or extensions or multiple lengths of IV tubing are used to connect the patient in the MRI suite to IV infusion pumps located further away in the MRI control room.

Long circuit tubing for the anesthesia machine circuit and the sampling catheter for monitoring respiratory gases (eg, end-tidal CO₂ and expired inhaled anesthetic concentrations) may be needed [3,5]. These extended tubing lengths are necessary because the distances between the patient and the anesthesia gas machine and/or infusion pumps for IV drugs may be 6 to 10 feet or sometimes more, depending on the layout of the imaging suite.

Positioning in the MRI suite — The strong, static magnetic field is generated by a superconducting electromagnet and is present at all times. Thus, positioning of the anesthesia machine, monitors, and other equipment within the MRI suite is carefully planned before, during, and after an imaging study. Collaboration with the MRI technologist is necessary to determine and demarcate the optimal and safe locations for movable anesthesia equipment in relation to the magnet [4,5].

The patient's position in the scanner depends upon the specific imaging requirements. During brain imaging, the patient is usually positioned with their head in the scanner and arms tucked at the sides, although positioning will vary for the specific scanning purposes. For example, lower extremity scans can be done with only the extremity in the scanner; for breast imaging, the patient is typically prone, with arms over the head. Consideration should be given to nerve injuries (ie, stretch of brachial plexus) that may occur in certain positions, particularly for patients under general anesthesia [10].

Typically, the anesthesiologist monitors the patient from a control room. If possible, configuration of the MRI suite setup allows the anesthesiologist to maintain an unobstructed view of the patient, anesthesia machine, and monitors, either by direct observation or on a video monitor. In some cases, IV infusion pumps that are not MRI safe are also located in the control room near the anesthesiologist, with long extension tubing connecting the pump to the patient's IV catheter. (See 'Anesthetic management of adult patients' below.)

Final configuration of the patient area should allow the anesthesiologist to view both the patient and the anesthesia machine and monitors during the procedure, either by direct observation or on a video monitor.

Minimizing potential delays in cardiopulmonary resuscitation — Initiation of cardiopulmonary resuscitation (CPR) may be delayed (defined as longer than two minutes after cardiac arrest). Delays occur due to the need for removal of the patient from the scanner, transfer to a stretcher, and relocation to a nearby location out of zone IV that is fully stocked with resuscitation equipment [3,5]. In the MRI suite, the powerful magnet can draw heavy equipment such as a defibrillator into the bore of the scanner, so the patient must be moved to an area just outside of the suite. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Safety zones'.)

Safety precautions that address these challenges include availability of MR-safe-conditional laryngoscopes and other airway equipment in the MRI suite to avoid inadvertent entry of MR-unsafe devices into zone IV near the scanner [11]. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Safety zones'.)

Furthermore, multidisciplinary team responses to airway and other emergencies such as cardiac arrest should be rehearsed, along with prearranged communication protocols to summon additional anesthesia personnel in an emergency [5,12]. Ideally, the "code team" responders are experienced with specific anesthetic-related causes of respiratory or cardiac arrest in adult or pediatric patients, as appropriate. Cognitive aids are particularly useful in this setting since radiology personnel may be unfamiliar with crisis management for anesthesia-related emergencies. (See "Cognitive aids for perioperative emergencies".)

Preanesthesia consultation: Special considerations for MRI procedures — The radiology team may consult anesthesia personnel to determine what type of anesthetic care is necessary in selected patients with severe anxiety or claustrophobia, inability to lie supine, inability to cooperate, obesity, a difficult airway, obtunded or comatose state after craniotomy, or hemodynamic instability. Underlying risks due to comorbidities are assessed; these may be exacerbated at both extremes of age (older adults and very young children) [4].

The preanesthesia consultation for patients undergoing MRI includes a review of the pathology for which the procedure is being performed and understanding the specific requirements for completion of the scan that may affect anesthetic care, as determined by the interventionalist or radiology team (eg, a need for frequent periods of apnea).

It is particularly important to identify factors that may cause patient injury or complications due to the MRI scanning equipment or administration of contrast agent [13].

●MRI safety

•Presence of implants – Although newer permanent PMs and ICDs may be MRI-conditional, many patients are still using older devices that were not designed to be compatible with MRI. Even with MRI-conditional PMs and ICDs, device-specific precautions during MRI are not uniform and should be checked with the manufacturer [5,14-17]. For patients with PMs and ICDs that are not MRI-conditional, if an MRI examination is indicated and necessary, scanning can be undertaken at a center with equipment and experience in performing such examinations if specific precautionary measures are in place [4,14,15,18]. Specific risks for use of MRI in patients with PMs or ICDs are discussed separately. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging".)

Risks for patients with other implantable cardiovascular devices such as a stent (eg, coronary arterial, aortic, or peripheral vascular stents), mechanical cardiac valve, inferior vena cava filter) are discussed separately [5]. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Cardiovascular implantable electronic device'.)

Also, risks for noncardiac implantable electronic medical devices (IEMDs) such as a deep brain stimulator, nerve stimulator, bone stimulator, or cochlear implant are described separately [5,19]. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Cardiovascular implantable electronic device'.)

Furthermore, transdermal patches (eg, fentanyl, lidocaine, scopolamine) may contain aluminum or other metals in their nonadhesive backing and should not be worn during MRI due to the risk of causing burns [5]. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging", section on 'Drug infusion pumps and patches'.)

•Need for continuous infusions – Patients receiving continuous infusions (eg, vasoactive infusions for hemodynamic instability) are at particularly high risk due to limited access to the patient and infusion pumps during MRI or CT scanning, as well as the absence of resuscitation equipment in the room that houses the MRI scanner.

•Pregnancy – Women who are or might be pregnant are informed that fetal safety remains unproven, although there have been no demonstrated untoward effects of MRI in pregnancy during more than 30 years of clinical use [5]. (See "Diagnostic imaging in pregnant and lactating patients", section on 'Magnetic resonance imaging'.)

●Risks of gadolinium – The anesthesiologist should not administer linear gadolinium contrast agent to patients with acute or severe renal insufficiency because of increased risk of nephrogenic systemic fibrosis [4,5]. Macrocyclic gadolinium agents that have not been associated with nephrogenic system fibrosis can be administered safely. (See "Patient evaluation for metallic or electrical implants, devices, or foreign bodies before magnetic resonance imaging".)

All gadolinium agents are avoided in pregnant patients as they cross the placenta and the health consequences to the fetus are unknown. (See "Diagnostic imaging in pregnant and lactating patients", section on 'Magnetic resonance imaging'.)

ANESTHETIC CHALLENGES FOR COMPUTED TOMOGRAPHY IMAGING

Physical location of the CT suite — Preparation for anesthetic management in a CT suite requires extra time compared with preparations in a standard operating room (similar to preparations in an MRI suite, interventional radiology suite, or other in-hospital settings that are in a remote location). Detailed discussion of these issues is available in a separate topic. (See "Considerations for non-operating room anesthesia (NORA)", section on 'Anesthetic challenges in non-operating room locations'.)

Communication in the CT suite — Similar to considerations in the MRI suite, communication challenges include a darkened room, distance to the patient, obstructed line of sight to the patient and monitors, and presence of a multidisciplinary team.

Radiation risks — Anesthesia care providers will be exposed to ionizing radiation if they are in the scanner room during a CT procedure. Protective strategies to mitigate radiation risk including distance from the source of ionizing radiation and use of portable shields, lead aprons, thyroid collars, and eye protection are discussed separately [20,21]. (See "Radiation-related risks of imaging" and "Considerations for non-operating room anesthesia (NORA)", section on 'Radiation risks'.)

Preanesthesia consultation: Special considerations for CT procedures — The radiology team may consult anesthesia personnel for selected patients with severe anxiety or claustrophobia, inability to lie supine, inability to cooperate, obesity, a difficult airway, obtunded or comatose state after craniotomy, or hemodynamic instability. The preanesthesia consultation for patients undergoing CT scanning involves reviewing the pathology for which the procedure is being performed and any specific requirements for completion of the scan. Women of childbearing age are also assessed for the possibility of pregnancy.

Positioning in the CT suite — Similar to MRI procedures, the anesthesiologist often monitors the patient from a control room. If possible, configuration of the room setup allows the anesthesiologist to maintain an unobstructed view of the patient, anesthesia machine, and monitors. (See 'Positioning in the MRI suite' above.)

Emergency management in the CT suite — Similar to the MRI suite, a prearranged communication protocol with anesthesiology and other personnel outside the MRI suite is necessary to ensure that response to an emergency is rapid [3,5,6] (see 'Minimizing potential delays in cardiopulmonary resuscitation' above). For pediatric cases, responding personnel should be subspecialized in pediatric resuscitation [12]. Cognitive aids are particularly useful in this setting since radiology personnel may be unfamiliar with crisis management for anesthesia-related pediatric emergencies. (See "Cognitive aids for perioperative emergencies".)

ANESTHETIC MANAGEMENT OF ADULT PATIENTS — Management during MRI or CT scanning includes selection of anesthetic techniques and agents as well as positioning of the patient, anesthetic equipment, and anesthesia personnel to provide optimal care.

Monitoring and equipment — Regardless of anesthetic technique, standard American Society of Anesthesiologists (ASA) monitoring (eg, electrocardiography [ECG], pulse oximetry [SpO₂], noninvasive blood pressure [NIBP] cuff measurements, capnography to monitor end-tidal CO₂ [ETCO₂]) is necessary to rapidly diagnose respiratory or cardiovascular instability (table 1). (See "Basic patient monitoring during anesthesia", section on 'Standards for monitoring during anesthesia'.)

All monitors and equipment used inside an MRI suite must be MRI safe/compatible (see 'Equipment' above). As noted above, positioning of anesthesia equipment and monitors is carefully planned in either an MRI or a CT suite. Especially in the MRI suite, the location of the monitor may be dictated by the limitations of an MR conditional monitor and the Gauss lines in the room. (See 'Positioning in the MRI suite' above and 'Positioning in the CT suite' above.)

Anesthetic techniques

Monitored anesthesia care (MAC) — Considerations for selection of an anesthetic technique for MRI or CT scanning procedures are similar to those for interventional radiology (IR) procedures (see "Considerations for non-operating room anesthesia (NORA)", section on 'Selection of anesthetic technique'). Minimal or deep sedation with monitored anesthesia care [MAC] is often selected, depending on procedure-specific and patient-specific considerations. Regardless of the type of anesthesia selected, the patient must remain immobile during the procedure since even very small movements cause image artifacts.

In some cases, conversion to general anesthesia becomes necessary; thus, the anesthesiologist should always be prepared to induce general anesthesia (table 2) [4-6].

General anesthesia

●Induction – If a general anesthetic is selected for an MRI procedure, induction of general anesthesia and establishment of airway access is typically completed in a holding area or induction room near the MRI suite, with subsequent transportation of the unconscious patient into the MRI suite, and then into the MRI scanner itself. For CT procedures, induction is typically accomplished inside the CT suite.

●Maintenance – Typically, a relatively light anesthetic depth may be maintained since there are no painful stimuli. However, the patient must remain immobile throughout the duration of the scan since even small movements cause artifacts in the image. If necessary, the scan is interrupted while the anesthesiologist leaves the control room to assure airway patency and/or administer a neuromuscular blocking agent (NMBA) to maintain immobility. If coughing or other movement occurs, anesthetic depth should be increased. In some cases, the patient's blood pressure is supported with a vasopressor (eg, phenylephrine) to maintain depth of anesthesia sufficient to prevent movement. (See "Hemodynamic management during anesthesia in adults", section on 'Selection and dosing of anesthetic agents'.)

Either an inhalation anesthetic technique, total intravenous anesthesia (TIVA), or a combination of these techniques may be employed to maintain general anesthesia.

•Inhalation technique – If an inhalation anesthetic technique is employed during MRI scanning, use of an MRI safe/conditional anesthesia machine is ideal. Sevoflurane is typically used since there are no MRI safe/conditional desflurane vaporizers. Also, an MRI compatible scavenging system should be used so that the medical staff does not inhale anesthetic gases [4]. (See "Maintenance of general anesthesia: Overview", section on 'Inhalation anesthetic agents and techniques'.)

In institutions that do not have an MRI safe/conditional anesthesia machine, an MRI unsafe machine may be used with an elongated breathing circuit through a "wave guide" (copper-lined conduit that maintains radiofrequency isolation), so that the machine can be located further away in zone III [4].

•TIVA technique – A TIVA technique is a reasonable alternative to an inhalation anesthetic (see "Maintenance of general anesthesia: Overview", section on 'Total intravenous anesthesia'). During a TIVA technique for MRI scanning, an MRI safe/conditional ventilator or other equipment should be available since administration of positive pressure ventilation with oxygen may become necessary.

If available, MRI safe/conditional infusion pumps are used to administer the IV agents. In some institutions, multiple lengths of IV tubing are used to connect the patient in the MRI suite to MRI unsafe infusion pumps that are located in the control room. However, if occlusion of the IV tubing or catheter occurs during slow (≤20 mL/hour) infusion of an agent, the pressure occlusion alarm may be delayed due to the length of the tubing [22]. Thus, awakening and movement may occur because the patient was not receiving the intended IV anesthetic agent(s).

ANESTHETIC MANAGEMENT OF PEDIATRIC PATIENTS — Infants and young children may be uncooperative and intolerant of relatively long periods of immobility required for MRI or CT scanning [23]. These patients occasionally require deep sedation or general anesthesia [24,25].

Location of the induction and recovery site — In some institutions, the site for preanesthetic evaluation, induction of sedation or general anesthesia, and subsequent recovery of an infant or child is at a central location specialized in pediatric anesthesia services (with subsequent transport to and then from the MRI or CT scanner). In other institutions, anesthetic induction and recovery are accomplished at the remote physical location of the scanning suite. There are advantages and disadvantages to each approach.

Induction and recovery at a central location — Advantages of induction and recovery at a central location include immediate availability of other subspecialized staff (anesthesiologists and anesthesia technicians) and equipment, which may be necessary for difficult airway management or intravenous (IV) access in a pediatric patient, or for emergency resuscitation during induction of anesthesia or recovery after the procedure.

Disadvantages include the need to transport the pediatric patient, which may be dangerous, particularly for those who are critically ill [26]. The following precautions may improve patient safety:

●Transport to the MRI or CT suite is accomplished with portable monitoring equipment and essential drugs. A mnemonic such as "SOAPME" (Suction, Oxygen, Airway equipment, Pharmacologic agents, Monitoring, special Equipment) or a formal checklist ensures that the following items are not forgotten [27]:

•Standard monitors (eg, electrocardiography [ECG], pulse oximetry [SpO₂], noninvasive blood pressure [NIBP] cuff, capnography to continuously monitor an end-tidal CO₂ [ETCO₂] waveform). A separate monitor may be necessary if ETCO₂ monitoring is not incorporated as a module in the institution's standard portable transport monitors. Protocols to ensure regular checks of all equipment are necessary.

•Emergency airway equipment, including suction catheters, masks, supraglottic airways, laryngoscopes, endotracheal tubes, and a self-inflating bag-mask device (eg, an Ambu bag).

•Anesthetic and other standard and emergency drugs (the checklist should include a list of essential drugs).

•Sufficient oxygen to ventilate the patient for a prolonged period (ie, until the patient is able to maintain his or her own airway), due to the possibility of an elevator breakdown during transport. In general, a full oxygen tank, which contains 660 L, should last long enough to transport the patient even if a delay occurs.

●Since the MRI and CT suites are typically remote from the main operating room (OR), the best route for transport is predetermined by the anesthesiology department or an institutional representative. Simulating management of problems that may occur during patient transport may decrease the risk of adverse events [28].

Induction and recovery near the MRI or CT scanner — Advantages of induction and recovery near the MRI or CT scanner include avoidance of the need for patient transport after induction of anesthesia or for recovery. This setup also facilitates parental presence during induction and recovery. In some institutions, time and cost savings are gained due to elimination of pre- and postprocedure transport times.

Disadvantages include the cost and availability of experienced pediatric nursing staff to manage care before and after the procedure, including at least one nurse for preoperative evaluation and two nurses for postoperative recovery. Another requirement is institutional build-out of space near the MRI or CT suite, with full monitoring and resuscitation capabilities for both the preoperative and postoperative periods. Protocols are necessary to ensure stocking and checking all routine and emergency drugs and equipment stored on-site (or in a recovery cart that is exchanged or restocked after each use).

General considerations — Pediatric patients who receive sedation or general anesthesia in MRI or CT suites have a high incidence of oxygen desaturation (2 to 12 percent), with such events occurring more commonly in those with developmental delay [23,29,30]. Underlying risks due to patient comorbidities may be exacerbated at both extremes of age (very young children and older adults) [4].

Anesthetic techniques for infants younger than six months — General anesthesia or propofol sedation is commonly used in infants and very young children, but this incurs side effects and risks (eg, intraoperative airway obstruction and post-anesthesia apnea), and is not necessary for all MRI or CT imaging procedures [31]. Although some studies note potential long-term neurocognitive and behavioral consequences for children who receive general anesthesia early in life, particularly if repeated anesthetics are necessary, there is little concern regarding a single anesthetic exposure [32,33]. (See "Neurotoxic effects of anesthetics on the developing brain".)

A "feed and swaddle" protocol may be employed in many young infants [34,35]. This involves feeding with breast milk, then laying the infant face-up with the head at the edge of a blanket over a folded corner. Each corner is brought across the baby and tucked. The infant's feet, legs, and hips can move freely to avoid injury. The infant then is soothed until he or she falls asleep naturally without anesthetic or sedative agents and can be placed in the scanner. A specialized safety strap is used to ensure that the infant does not kick or roll off the narrow imaging table. If the infant awakens and moves, the scan is interrupted for additional soothing. This technique was used in a retrospective review of 164 infants undergoing brain MRI, with a diagnostic success rate of >90 percent in term infants ≤181 days old, as well as in preterm infants [35]. Similarly, the diagnostic success rate was 96 percent in a small observational study in 24 infants <6 months old undergoing cardiac MRI or CT angiography procedures for aortic arch abnormalities [36]. Although this technique requires additional time, risk for the infant is minimized compared with sedation or general anesthesia. (See 'Sedation' below and 'General anesthesia' below.)

An alternative technique for neonates is sedation with intranasal dexmedetomidine 3 mcg/kg together with intranasal midazolam 0.2 mcg/kg [37]. Peripheral intravenous (IV) access was established after intranasal administration of these sedatives but before beginning MRI scanning.

Another strategy for infants who are swaddled and young children who are unable to comply with breathing instructions, newer MRI techniques such as single-shot fast spin echo or volumetric gradient echo can decrease artifacts and improve imaging quality, while techniques such as respiratory triggering and signal averaging may adequately reduce respiratory motion artifact [38].

Anesthetic techniques for older infants and children — Although many younger children will require sedative agents, children over five years old may be able to complete the imaging procedure with none [39]. Techniques such as allowing the parent/caregiver to stay with the patient in the imaging room, distraction with goggles projecting a movie, or simple reassurance may alleviate the need for sedation. In one study, a mock scanner was used to expose children to the MRI environment [40]. The resulting behavioral desensitization allowed 72 percent of children to complete an MRI on their first attempt.

Sedation — For those children who require sedation or general anesthesia, monitoring and equipment considerations are similar to those for adult patients undergoing MRI or CT scanning. Thus, standard American Society of Anesthesiologists (ASA) monitoring (eg, electrocardiography [ECG], pulse oximetry [SpO₂], noninvasive blood pressure [NIBP] cuff measurements, and capnography to monitor end-tidal CO₂ [ETCO₂]) is necessary to rapidly diagnose respiratory or cardiovascular instability (table 1) [1]. In the MRI suite, monitors, anesthesia machine, and laryngoscopes, stylets, and stethoscopes must be MRI safe/compatible. (See "Basic patient monitoring during anesthesia" and 'Equipment' above.)

As noted above, a natural airway and spontaneous ventilation are maintained if possible. Sedation for CT and MRI are discussed separately. (See "Procedural sedation in children: Selection of medications", section on 'Sedation for imaging studies'.)

General anesthesia — General anesthesia may be necessary for a pediatric patient unable to tolerate the procedure. Examples include ex-premature infants who are more sensitive to the respiratory depressant effects of sedative medications and opioids and are thus prone to apnea, children with obstructive sleep apnea (OSA) or symptomatic gastroesophageal reflux, or adolescents with developmental delay. Controlled ventilation and breath-holding may also be necessary to minimize motion artifact during MRI [24,29,30,41,42].

Airway management — The type of airway support is selected based on the patient's comorbidities.

●Oxygen administered via nasal cannula – In some pediatric patients without comorbidities such as airway abnormality, sleep apnea, or obesity, a general anesthetic may be employed with delivery of oxygen via nasal cannula with maintenance of spontaneous respiration. Placement of a shoulder roll (ie, a rolled blanket positioned under the shoulders) facilitates maintenance of an open airway by anteriorly displacing the tongue and submental tissues [43].

●Oxygen administered via oral airway or nasal trumpet – If necessary, use of an oral airway or nasal trumpet facilitates airway opening and may preclude the need for more advanced airway management (eg, endotracheal intubation).

●Laryngeal mask airway (supraglottic airway) – A laryngeal mask airway (LMA; also known as a supraglottic airway [SGA]) is another option in a child with a normal airway who is not at risk for aspiration.

●Endotracheal intubation – Endotracheal intubation is required in a child with an abnormal airway or risk for aspiration. In addition to standard ASA monitoring, continuous ETCO₂ and intermittent airway pressures and volumes are monitored after the airway has been secured.

Pediatric patients with a history of frequent poorly controlled seizures typically require general endotracheal anesthesia to maintain immobility during an imaging study. Often, these patients are chronically receiving phenobarbital for seizure control, which results in higher than normal hepatic cytochrome P-450 enzyme levels, and a higher clearance of anesthetics and other drugs [44]. Dosing of the primary anesthetic agent is increased as needed, and/or multiple anesthetic agents may be employed. (See 'Anesthetic agents' below.)

Ventilation management — Many patients can be allowed to breathe spontaneously if the imaging procedure is brief. However, small patients or those with neuromuscular weakness might not be able to overcome the resistance of the breathing circuit during spontaneous breathing, particularly if very long tubing is required to connect the patient to a ventilator that is located outside of the scanner room. Controlled mechanical ventilation is typically used for these patients, although continuous positive airway pressure has also been described [45].

Temperature management — An MRI safe/compatible temperature probe is also necessary for all infants and children. Interference with normal thermal regulation during general anesthesia often results in hypothermia [1,46]. Conversely, the radiofrequency radiation emitted by the MRI scanner generates heat energy that may be absorbed by the patient, causing hyperthermia [47].

Anesthetic agents — If general anesthesia is necessary to accomplish MRI or CT scanning in a pediatric patient, induction is typically accomplished with intravenous propofol or inhaled sevoflurane. For maintenance, either an inhalation anesthetic technique, a total intravenous anesthetic (TIVA) technique with infusion of one or more IV anesthetic agents, or a combination of these techniques may be employed [30,41,48,49].

●Volatile anesthetic agents – Similar to general anesthesia in adult patients, an MRI safe/compatible anesthesia machine with an appropriate scavenging system is employed for delivery of inhalation anesthetics (see 'Anesthetic techniques' above). Use of potent volatile anesthetic agents allows rapid recovery and eliminates the need for multiple MRI safe/compatible infusion pumps. However, inhalation anesthetic agents cannot be delivered via an MRI safe ventilator from a neonatal or pediatric intensive care unit (ICU) in a patient who requires specialized ventilator settings.

Sevoflurane is the only potent volatile anesthetic agent used for induction and is typically the only volatile anesthetic available on anesthesia machines in the MRI or CT suite. Induction of anesthesia for an MRI scan typically occurs in an area immediately outside the MRI suite, followed by immediate insertion of an IV catheter. Subsequently, the patient may be moved into the MRI suite for maintenance of general anesthesia with either sevoflurane and/or IV agents.

One large retrospective study of 7129 pediatric patients receiving sevoflurane anesthesia for MRI noted only 28 severe airway-related adverse events (0.4 percent, CI 0.2-0.5 percent), with the most common being apnea or airway obstruction [50].

●Intravenous anesthetic agents – If IV anesthetic agent(s) are administered, MRI safe/compatible infusion pumps are preferred for patients undergoing MRI scanning, as noted above. This is particularly important in pediatric patients because a slow infusion of IV agents (eg, ≤20 mL/hour) is used in small patients. Long lengths of IV tubing should therefore be avoided because they may become kinked (or the IV may become infiltrated) for some time before the pump's pressure alarm activates [22]. (See 'General anesthesia' above.)

•Propofol – Propofol is commonly used in both children and adults because of its rapid onset and recovery, antiemetic effects, and other properties. Its side effect profile is also relatively benign (table 3) [1,42,48,49]. (See "General anesthesia: Intravenous induction agents", section on 'Propofol'.)

Propofol may be used as a sole agent for pediatric MRI or CT when administered at a maintenance dose of 100 to 300 mcg/kg per minute, titrated to effect and hemodynamic stability [51] (see "Maintenance of general anesthesia: Overview", section on 'Sedative-hypnotic agent: Propofol'). One study concluded that propofol was superior to dexmedetomidine due to more satisfactory emergence from general anesthesia and better parental satisfaction [52]. Alternative strategies employ a combination of propofol with other IV agents (eg, a benzodiazepine, opioid, dexmedetomidine, ketamine) to reduce the total propofol dose [53-57].

•Dexmedetomidine – Dexmedetomidine is an alpha₂ receptor agonist that provides dose-dependent sedation, analgesia, sympatholysis, and anxiolysis, with a redistribution half-life of six minutes. (See "Maintenance of general anesthesia: Overview", section on 'Dexmedetomidine'.)

Dexmedetomidine is typically used in combination with other IV agents (eg, propofol, ketamine, fentanyl, midazolam) [41,53,57,58].

For example, a loading dose of dexmedetomidine has been administered as a bolus of 0.5 mcg/kg (or as a rapid infusion of 1 to 2 mcg/kg administered over 5 to 10 minutes), followed by administration of propofol as needed [57,59]. This combination of agents has resulted in fewer sedation-related adverse events, particularly upper airway obstruction, compared with administration of propofol alone.

Another example is the combination of dexmedetomidine 1 mcg/kg and ketamine 1 mg/kg for induction, followed by maintenance with dexmedetomidine at 0.2 to 0.7 mcg/kg per hour [58]. This combination may be selected in patients with respiratory or hemodynamic compromise, since both dexmedetomidine and ketamine maintain airway reflexes and respiratory drive, while ketamine typically increases blood pressure (BP), heart rate (HR), and cardiac output (CO), as noted below.

Although dexmedetomidine has been used as the sole anesthetic agent [51,60,61], many patients require additional medications [62].

•Ketamine – Ketamine is an induction agent that produces dissociative anesthesia (profound analgesia while appearing disconnected from surroundings), acting as an N-methyl-D-aspartate (NMDA) antagonist and an opioid receptor agonist. It is the only anesthetic agent that stimulates catecholamine receptors, thereby producing increases in BP, HR, CO, and cerebral blood flow. Ketamine may be administered IV, or via an intramuscular dose in a child without IV access (table 3). However, ketamine is rarely selected for induction since large doses may cause hallucinations and increased secretions, although administration of midazolam and glycopyrrolate as adjuvant agents mitigates these side effects. (See "General anesthesia: Intravenous induction agents", section on 'Ketamine'.)

A maintenance dose of ketamine 2.5 to 5 mcg/kg per minute may be administered in combination with other agents (eg, dexmedetomidine, propofol, remifentanil) [41,56,58] (see "Maintenance of general anesthesia: Overview", section on 'Ketamine'). Ketamine has a good safety profile for pediatric patients undergoing MRI, CT, and other procedures outside of the main OR. One observational study of 22,645 pediatric patients who received ketamine during such procedures noted zero mortality and a low incidence (1.8 percent) of serious adverse events such as laryngospasm [63].

•Remifentanil – Remifentanil is an ultrashort-acting opioid that acts on mu-opioid receptors. Its primary benefit is its very rapid onset and offset (table 4). Advantages of a rapid recovery time include the potential for increased parent satisfaction, as well as increased efficiency. (See "General anesthesia: Intravenous induction agents", section on 'Opioids' and "Maintenance of general anesthesia: Overview", section on 'Analgesic component: Opioid agents'.)

Remifentanil may be used in combination with other agents (eg, propofol) for pediatric MRI or CT scanning, typically as a continuous infusion at 0.05 to 0.1 mcg/kg per minute administered during and/or shortly after induction. Patients are closely monitored to avoid respiratory depression during the infusion, but other opioid-induced adverse effects are rare at these low doses (eg, postoperative nausea and vomiting, chest wall rigidity, significant bradycardia requiring treatment) [54].

•Avoid chloral hydrate – Chloral hydrate is avoided because it can be fatal even at therapeutic doses due to resedation at home after discharge [64]. Resedation is due to the long elimination half-life of the active metabolite of chloral hydrate, which is 8 to 12 hours at recommended doses, but may be as long as 35 hours after higher doses.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Procedural sedation in adults".)

SUMMARY AND RECOMMENDATIONS

●Challenges for anesthetic management in the MRI and CT suites

•Remote setting – Challenges for anesthetic management of patients undergoing either magnetic resonance imaging (MRI) or computed tomography (CT) procedures include settings that are remote from the main operating rooms. (See 'Physical location of the MRI suite' above and 'Physical location of the CT suite' above.)

•Communication challenges – Communication in the MRI or CT suite can be difficult due to a darkened room, distance and obstructed line of sight to the patient and monitors, and presence of a multidisciplinary team. Loud acoustic noise and the need to wear hearing protectors pose additional challenges in MRI suites. (See 'Communication in the MRI suite' above and 'Communication in the CT suite' above.)

•Risks due to scanning equipment include:

-For MRI scanning, the strong static magnetic field may cause objects to become projectile, radiofrequency energy may cause tissue or device heating, electromagnetic interference (EMI) may cause artifacts that limit clinical interpretation of the electrocardiogram (ECG) and other waveforms, and loud acoustic noise may cause communications difficulties and hearing loss. (See 'Environmental risks and challenges' above.)

-For CT scanning, the risk is exposure to ionizing radiation. (See 'Radiation risks' above.)

•Positioning the patient and equipment – Positioning of the anesthesia machine, monitors, and other equipment within the MRI suite is planned in collaboration with MRI personnel to determine optimal and safe locations for all anesthesia equipment in relation to the MRI magnet (figure 1). Typically, the anesthesiologist monitors the patient from a control room in the MRI or CT suite, with configuration of the room setup to allow an unobstructed view of the anesthesia machine, monitors, and patient, either by direct observation or on a video monitor. (See 'Positioning in the MRI suite' above and 'Positioning in the CT suite' above.)

•Special considerations for equipment in the MRI suite – All monitors and equipment should be MRI safe/compatible, including the anesthesia machine itself, infusion pumps for administration of intravenous (IV) agents, and laryngoscope handles, blades, stylets, and stethoscopes. (See 'Equipment' above.)

•Challenges in emergency management – Prearrange communication protocols with anesthesiology and other personnel outside the MRI or CT suite to ensure rapid response. Delays due to the need to remove the patient from the scanner, placement onto a stretcher, and relocation to a nearby environment fully stocked with resuscitation equipment should be minimized. Cognitive aids are particularly useful in these settings. (See 'Minimizing potential delays in cardiopulmonary resuscitation' above and 'Emergency management in the CT suite' above and "Cognitive aids for perioperative emergencies".)

●Preanesthesia consultation – The preanesthesia consultation for patients undergoing MRI or CT scanning involves assessing the pathology for which the procedure is being performed and specific requirements for completion of the scan (eg, frequent periods of apnea). Comorbidities or hemodynamic instability that may affect anesthetic administration is assessed, and factors are identified that may cause complications due to MRI equipment (eg, a pacemaker, implantable cardioverter-defibrillator [ICD], implanted nerve stimulator, other ferromagnetic implants), or radiation exposure during CT (eg, pregnancy). (See 'Preanesthesia consultation: Special considerations for MRI procedures' above and 'Preanesthesia consultation: Special considerations for CT procedures' above.)

●Anesthetic management of adult patients

•Monitored anesthesia care – Minimal or deep sedation with monitored anesthesia care [MAC] is often selected. The patient must remain immobile during the procedure since even very small movements cause image artifacts. The anesthesiologist should always be prepared to induce general anesthesia if necessary. (See 'Monitored anesthesia care (MAC)' above.)

•General anesthesia – Either an inhalation anesthetic technique, total intravenous anesthesia (TIVA), or a combination of these techniques may be used if general anesthesia is necessary in an adult patient. Sevoflurane is employed if a volatile inhalation anesthetic is selected during MRI scanning since MRI safe/conditional vaporizers for other agents are not available. (See 'General anesthesia' above.)

●Anesthetic management of pediatric patients

•Infants <6 months old – General anesthesia is not indicated for a nonpainful MRI or CT procedure in an infant less than six months old. Typically, a “feed and swaddle” technique is employed, whereby the infant is fed breast or bottle milk, then swaddled and soothed until he falls asleep naturally, followed by placement in the scanner without anesthetic or sedative agents. (See 'Anesthetic techniques for infants younger than six months' above.)

•Older infants and children – For children undergoing MRI or CT scanning, a natural airway and spontaneous ventilation is maintained if possible. Many older pediatric patients tolerate brief MRI or CT scans after a dose of oral or nasal midazolam. Older pediatric and teenaged patients typically tolerate longer scans with small bolus doses of IV midazolam and fentanyl. (See 'Anesthetic techniques for older infants and children' above.)

•General anesthesia considerations – If general anesthesia is necessary in a pediatric patient, the type of airway support is selected based on the patient's comorbidities. Induction is typically accomplished with intravenous propofol or inhaled sevoflurane. For maintenance, either an inhalation anesthetic technique with sevoflurane, a TIVA technique with infusion of one or more anesthetic agents (eg, propofol, dexmedetomidine, ketamine, remifentanil), or a combination of these techniques may be employed. (See 'General anesthesia' above.)