| |
June 2002
Volume 66 |
Number 6
|
| |
|
| Being Extra Safe
When Providing Anesthesia for MRI Examinations |
Lawrence Litt, Ph.D., M.D.
Charles B. Cauldwell, M.D.
Last July, shocking reports of an anesthesia-related hospital
accident burst into newspaper headlines and prime-time news programs
across the nation. A sedated 6-year-old boy undergoing a magnetic
resonance imaging (MRI) examination died after being struck in
the head by an iron oxygen tank that allegedly had been brought
into the magnet room by an anesthesiologist.
A follow-up Emergency Care Research Institute report in August
titled "Patient Death Illustrates the Importance of Adhering
to Safety Precautions in Magnetic Resonance Environments"
pointed out 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.
Magnets and Missiles
Only certain metals, iron, nickel and cobalt to name a few, are
magnetic. Items made of nonmagnetic aluminum, titanium, copper,
silver and gold are safe as far as missile dangers are concerned
and are among the materials used to make MR-compatible intravenous
(I.V.) poles, fixation devices and nonmagnetic anesthesia machines.
Often one must bring into the MRI magnet room susceptible metal
items such as infusion pumps for I.V. lines. In such cases, it
is safer to position those objects in the magnet room before the
patient enters the magnet bore.
What about implanted metals such as hip prostheses and Harrington
rods, which are made of stainless steel, a metal usually only
weakly magnetic? Leave such questions to your radiology colleagues.
Issues with large, weakly magnetic metal objects are usually about
image degradation not about the patient experiencing an uncontrollable
magnetic force. Metals do not need to be missiles to be dangerous
to the patient. Dangers from wires in epidural or Swan-Ganz catheters
are instead related to radiofrequency (RF) pulsing, which can
induce currents in wires and cause electric shocks or dangerous
heating that can melt the catheter wall.
The electric currents in superconducting magnets experience almost
no ohmic resistance because they are in metal coils cooled by
thousands of liters of liquid helium and liquid nitrogen. Strong
jolts to a superconducting magnet can cause a "quench,"
which is the destruction of the superconducting state. During
a quench, the liquid gases, heated by the ohmic resistance losses
that have returned, are supposed to exit the room via venting
stacks. Having the liquid gases evaporate elsewhere avoids a potentially
dangerous decrease in room oxygen tension.
What should one do if the unthinkable occurs and a missile does
fly into the magnet, causing injury while pinning the patient
to the inside of the bore? We have been taught that the magnet
is always on and that the magnetic field is always there, something
that is true so long as a superconducting electric current is
maintained. In fact, all superconducting magnets can be turned
off immediately. However, this is something that should be done
only by MRI technicians, and while it is being done, the anesthesiologist
should be removing the patient out of the magnet.
None of the above information should deter anesthesiologists
from feeling safe while being with a patient in the magnet room
during MR imaging. Noise levels can get high during MR imaging.
As MRI scans are acquired, everyone in the magnet room, including
the patient, should be wearing ear plugs, another potential obstacle
to good communications! Anesthesiologists in the magnet room can
provide additional safety, especially if they are positioned near
the door, ready to stop and check anyone who seems to be entering
with metal objects.
The MRI Anesthesia Station
The MRI-compatible equipment that goes into the magnet room is
really a second anesthesia station. Thus it is crucial that a
primary anesthesia station be located in an adjacent area just
outside the magnet room. If a potentially life-threatening problem
arises, it must be possible to briskly take the patient out of
the magnet to the primary anesthesia station where everything
is ready for optimum care. When doing the reverse, taking the
patient from the primary station into the magnet room, all physiological
monitoring devices must be MRI-compatible. If the fiberoptic pulse
oximeter in the magnet room does not work, one is forbidden to
take the standard pulse oximeter from the outside station and
bring it into the magnet room. Serious patient burns could result.
Logistics
Many logistical details require earlier interactions and preparations.
Before starting the day's cases, the anesthesiologist should have
the names, beeper numbers and telephone numbers of anesthesia
work room personnel who are known to be available. When anesthesia
is induced, we regularly have either a trained nurse or second
anesthesiologist assisting until the patient is stable inside
the magnet. While this second person is not obliged to stay during
the scan, he or she is expected to return for emergence at the
end of the case.
Patient-Related Issues
The selection of patients who receive care from an anesthesiologist
for MRI examinations differs from one institution to another.
At the University of California-San Francisco, almost all children
are deeply sedated/anesthetized by anesthesiologists as are adults
who need more than anxiolysis. In other hospitals, especially
in children's hospitals, nurses based in the radiology department
often deliver sedation under guidelines jointly arrived at by
the anesthesiology and radiology departments, with anesthesiologists
being brought in only when a patient is complicated or unstable.
Collaborative arrangements among physicians and administrative
and clinical nurses should be arranged in advance. Anesthesiologists
are often central to establishing systems that will minimize problems.
Organizing the scheduling of cases is particularly important both
for providing optimum patient care and efficiently using physician
and MRI instrument time. Pediatric cases at the University of
California-San Francisco are bunched during certain hours on certain
days. When cases must be done at other times, the MRI scheduler
communicates with a pediatric anesthesiologist who is in liaison.
Occasionally, parents will have a question several days before
the examination, in which case we will contact them immediately
by telephone. For all cases, however, anesthesiologists or nurses
contact the parents or guardians on the day before the procedure
in order to remind them of where and when to come and to communicate
nothing-by-mouth (NPO) times. We follow the current ASA guidelines
for NPO recommendations < www.ASAhq.org/practice/npo/npoguide.html
>. Most pediatric outpatients, while not seen prior to the day
of the MRI study, are met and examined in the induction area by
staff anesthesiologists. In contrast, many adult patients are
seen one or two days before the procedure in our anesthesia preoperative
clinic. Questionnaires regarding implanted metal objects, such
as a pacemaker, are filled out at the time of scheduling, and
a final screening is done on the day of the examination.
The location and method of emergence and recovery depends upon
the individual situation. We use propofol for the vast majority
of cases and find that adults and children both recover quite
quickly. Recovery usually takes place in the secondary anesthesia
area outside the magnet room, with patients going home directly.
If, however, an MRI scan has been quite long or if an infant or
adult is sick or just waking up slowly, such a patient is transported
either to the postanesthesia recovery room outside the operating
rooms or to a recovery area in the radiology department where
there are other patients who have been sedated for their procedure.
If MRI cases involving sedation/anesthesia are scheduled sequentially,
the anesthesia staff is presented with a dilemma. Should he or
she completely recover the first patient before starting to screen
or induce the second one? MRI scanner time costs thousands of
dollars per hour, and optimum MRI use would have no delay in turnover.
There is no absolute right or wrong here except that proper care
for both patients must be provided, and anesthesiologists should
not be inappropriately pressured into starting another case. With
additional support personnel in the context of rapid and uncomplicated
emergence, it is often possible to have a rapid turnover.
In January 2001, the Joint Commission of Accreditation of Healthcare
Organizations, in its "Comprehensive Accreditation Manual,"
put into effect its revised standards for sedation and anesthesia
care < www.jcaho.org/standard/aneshap.html
>. This document addresses many relevant issues, including the
need for continued monitoring of outcomes measures. Sedation/anesthesia
programs for MRI examinations are dynamic, and regular evaluation
is needed to identify new opportunities to improve care.
Final Word
Back in 1988 when the evolution of quality assurance was relatively
new, there was an interesting article by J. R. Gumpert titled
"Why on Earth Do Surgeons Need Quality Assurance?" [Ann
R Coll Surg Engl. 70(2): 85-92]. In it he introduced an acronym
meant to encompass all FACETs of medical care. A good physician,
he wrote, properly organizes the Finances, Administration, Communication
and Education of his team as well as the patient's Treatment.
The MRI accident last July lets us add a big "S" for
Safety, also one of the FACETS of our job.
References:
1. Archibold RC Hospital details failures leading to MRI fatality.
The New York Times. August 22, 2001:1.
2. Report of ECRI (formerly the Emergency Care Research Institute).
< www.ecri.org/documents/hazard_MRI_080601.pdf
> .
3. Anesthesia in Remote Locations Safety [videotape]. American
Society of Anesthesiologists; 1997. Patient Safety Videotape Series:
Videotape no. 26 < www.asahq.org/NEWSLETTERS/1997/12_97/
Anesthesia_1297.html >.
| |
|
Lawrence
Litt, Ph.D., M.D., is Professor of Anesthesiology and Radiology
at the University of California-San Francisco. |
|
| |
|
Charles
B. Cauldwell, M.D., is Professor of Anesthesiology and Pediatrics
at the University of California-San Francisco. |
|
return to top
|