To the Editor:— Since the first report of anesthesia for magnetic resonance imaging (MRI) in 1984, 1anesthesiologists increasingly cover MRI procedures, mostly in children and infants. We report a near-miss accident during MRI in a child due to a sevoflurane vaporizer brought into the MRI suite.
A 2-yr-old boy with retroperitoneal rhabdomyosarcoma was scheduled to undergo abdominal MRI. Anesthesia was provided by an anesthesiologist/nurse team with experience in anesthesia for MRI. After a check for removal of all ferromagnetic materials and of the MRI compatible ventilator (Titus MRI; Dräger, Lübeck, Germany), anesthesia was induced and maintained via a closely fitting facemask in the spontaneously breathing child using sevoflurane–nitrous oxide in 50% oxygen, and vital signs were monitored using MRI-safe equipment (graphite electrocardiogram leads, fiberoptic pulse oximetry, end-expiratory carbon dioxide, noninvasive blood pressure).
When a low level of sevoflurane was noted in the vaporizer (model 19.3; Dräger), the nurse was asked to refill it. However, because a refill bottle of sevoflurane was not immediately found, the nurse instead carried a portable sevoflurane vaporizer from the induction room into the MRI suite. Neither she nor the anesthesiologist considered that the almost empty sevoflurane vaporizer in the MRI suite was unremovably fixed to the ventilator and hence could not be replaced at all.
When the nurse put the vaporizer on the examination table (approximately 150 cm from the bore of the magnet, just beyond the 40-mT line), it was rapidly attracted toward the 1.5-T magnet. It was only by the force of four hands that the vaporizer could be directed to strike against the gantry instead of flying directly into the magnet, where it might have hit the child. However, a strong attraction toward the bore of the magnet was still felt, and the vaporizer could hardly be maintained at the side of the gantry.
The table with the sleeping child was rapidly moved out of the gantry, avoiding further danger. “Quenching,”i.e. , emergency release of liquid helium from the superconducting magnet coils with collapse of the magnetic field, was initially considered, but the vaporizer could be removed from the gantry with the help of a third person. Fortunately, neither the child nor the MRI machine were harmed, and the examination went on without further complications after excluding MRI damage and refilling the fixed vaporizer.
Furthermore, immediately after the accident the portable vaporizer was tested for magnetism with a handheld horseshoe magnet (RS Electronic, Mörfelden-Waldorf, Germany; length, 8 cm; width, 1 cm). However, no attraction was seen.
This is the first report, to our knowledge, of a near-miss accident in an MRI involving a portable vaporizer considered MRI-safe when fixed to a rack. Furthermore, the hazard was undetectable by using a powerful handheld magnet.
Contact with the manufacturer (Dräger Medical) revealed that this vaporizer contains ferromagnetic material in the temperature compensation module. An exchange of this material by nonmagnetic materials is impossible. The user manual of this vaporizer also contains a warning to change vaporizers only outside an MRI suite and to not put the vaporizer down in the MRI suite because it contains ferromagnetic parts and can be attracted by the MRI magnet. It also states that its use is safe for magnetic fields up to 70 mT, when the vaporizer is fixed to an MRI-safe ventilator.
Mainly, this near-miss accident was evoked by human error and communication lapse, which is by far the most important hazard in the MRI suite. First, neither the anesthesiologist nor the nurse was aware of the unremovable fixation of the vaporizer to the ventilator rack. In fact, this was specifically done to avoid an accident evoked by changing a vaporizer inside the MRI suite. Second, both were unaware of the warning in the user manual of this vaporizer regarding its use in the MRI suite.
The greatest hazard results from “projectile” or “missile” effects of ferromagnetic materials brought into the magnetic field. Of five reported accidents, two happened while inexperienced personal brought metal oxygen cylinders into an MRI suite, resulting in a serious facial fracture in one patient. 2In the other three cases, anesthesia or radiology personnel confused aluminum oxygen cylinders (MRI compatible) with metal oxygen cylinders, causing remarkable damage to the MRI machine. 2
Inattentiveness to hazards even caused by MRI-compatible anesthetic equipment has been also reported, 3as evidenced by an “MRI-compatible” anesthetic monitor (weight, 25 kg) rapidly attracted into the opening of the magnet when crossing the 40-mT line. The (small print) recommendations of the user manual had not been read before use.
Even MRI-compatible machines may contain ferromagnetic materials and bear risks when violating safety rules. Of note, even a test with a small handheld magnet likely would not have prevented the accident because of the heavy weight of the vaporizer and its small, hidden ferromagnetic parts. In another case, a pillow containing metal springs not detectable by a handheld magnet flew into the magnet during positioning of a patient, fortunately without causing injury. 4
Different concepts may increase patient safety during MRI, including completing an MRI safety form in a four-step process from ward to patient transport, MRI coordinator, and technologists. Furthermore, personnel with MRI access can be educated with safety videos demonstrating dangers. In addition, all equipment allowed in the MRI can be marked with fluorescent stickers as “MRI safe.”5Our case altered departmental safety rules for MRI procedures. First, it was reinforced that only educated and instructed personnel are allowed to provide anesthesia for MRI, and additional safety courses are offered monthly by the radiology department. Second, all anesthesia nurses now work in the MRI suite for rotations of at least 3 months.
In summary, the attracted “flying vaporizer” highlights the dangers of weak ferromagnetic objects, undetectable by routine testing, when brought into the magnetic field as well as the dangers of deviating from the established protocol. The death of a child caused by a missile oxygen cylinder 6has focused both public and professional attention on MRI safety. In an American Society of Anesthesiologists newsletter after that accident, the authors’ message is that because “we have known for decades about MRI magnets being able to violently suck in heavy metal objects, this accident tells us about a challenge that goes beyond requiring physicians to understand basic MRI safety principles. That challenge is to inculcate everyone with safety habits and protocols that are always followed, with no exceptions.”7Human error can only be minimized by consequent and repetitive teaching of all personal with MRI access.
Klinik für Anästhesiologie und Intensivmedizin, Universitätsklinikum Essen, Essen, Germany. christian.zimmer@uni-essen.de
