Anesthesia for MRI

The physical environment of the MRI suite presents several challenges for anesthetizing patients.

1. The long, narrow bore of the magnet in which the patient reclines does not allow ready access to or viewing of the patient during imaging. Scanners are located in shielded rooms that contain the magnetic field and shield against radiofrequency noise that would produce image artifact.
2. The static magnetic field is present at all times and exerts a force on all ferromagnetic materials (e.g., steel gas tanks, batteries, and standard stethoscopes). Ferromagnetic objects brought near the magnetic field can be forcibly pulled toward the magnet, potentially injuring people or equipment in their path. The static field and magnetic gradients generated during scanning can interfere with mechanical components (solenoids) in automated noninvasive blood pressure monitors, ventilators, and infusion pumps; specialized compatible equipment is necessary. Only plastic stethoscopes and commercially available magnet-compatible laryngoscopes should be used in the magnet area. Credit cards, watches, and pagers must be left outside the scanning room.
3. Radiofrequency signals and shifting magnetic fields generated during scanning may lead artifacts on the ECG and pulse oximeter.
4. Metallic implants (e.g., joint prostheses, aneurysm clips, and cochlear implants) or implanted devices (e.g., pacemakers, implantable cardioverter defibrillators [ICDs], insulin infusion pumps, intrathecal pumps, or spinal cord stimulators) may potentially be dislodged, dysfunction, or suffer permanent damage by the magnetic field, and scanning or heating may occur from radiofrequency signals generated during scanning. Some specific pacemakers, ICDs, or pulmonary artery catheters are considered “MRI safe,” and patients with these devices may undergo MRI scanning. Imaging of patients with these devices should not be considered routine, and individual cases should be carefully reviewed for medical necessity. Imaging may require that the pacemaker be turned off while the patient is in the magnetic field; the device is turned on after scanning. Cerebral aneurysm clips are not considered an absolute contraindication to MRI; it is important, however, to identify the type of clip present to determine MR compatibility. Not all clips are compatible. Each MRI site carries a list of medical devices designated MRI compatible by the U.S. Food and Drug Administration (FDA). Because medical devices may be upgraded or altered by a manufacturer without notifying the FDA, MRI centers should, in addition, contact the manufacturer if questions arise about specific devices.