General Policies and Procedures
Monitoring during an MRI procedure is indicated whenever a
patient requires observations of vital physiologic
parameters due to an underlying health problem or is unable
to respond or alert the MRI technologist or other healthcare
professional regarding pain, respiratory problem, cardiac
distress, or difficulty that might arise during the
examination (3, 4). In addition, a patient should be
monitored if there is a greater potential for a change in
physiologic status during the MRI procedure.
Table 1 summarizes the patients
that require monitoring and support during MRI procedures.
Besides patient monitoring, various support devices and
accessories may be needed for use in high-risk patients to
ensure safety (3, 4).
Table 1. Patients that require monitoring and support
during MRI procedures.
-Physically or mentally unstable patients.
-Patients with compromised physiologic functions.
-Patients who are unable to communicate.
-Neonatal and pediatric patients.
-Sedated or anesthetized patients.
-Patients undergoing MR-guided interventional procedures.
-Patients who may have a reaction to an MRI contrast agent
-Critically-ill or high-risk patients.
Patients undergoing MRI examinations while under sedation or
general anesthesia require the same standard of care as
provided in operating rooms and intensive care units
(ICU)(5). This includes monitoring vital physiological
parameters including the electrocardiogram (ECG), oxygen
saturation, blood pressure, end tidal carbon dioxide (CO2),
and body temperature (6, 7). The use of sedation or
anesthesia is necessary for certain MRI examinations,
especially for pediatric or critically-ill patients (3, 8).
Importantly, children represent the largest group requiring
sedation for MRI exams (3, 8). Sedation is used on children
to minimize discomfort, motion and anxiety during the
procedure (8, 9). The American Academy of Pediatrics and the
American College of Radiology have published guidelines for
monitoring children and adults during sedation (8, 10). The
vital signs that must be monitored include the heart rate,
blood pressure, respiratory rate, and temperature (8).
Because of the widespread use of MRI contrast agents and the
potential for adverse effects or idiosyncratic reactions to
occur, it is prudent to have appropriate monitoring
equipment and accessories readily available for the proper
management and support of patients who may experience
side-effects. This is emphasized because adverse events,
while extremely rare, may be serious or life threatening. In
addition, patients may have adverse reactions to other
medications while undergoing MRI procedures.
In 1992, the Safety Committee of the Society for Magnetic
Resonance Imaging published guidelines and recommendations
concerning the monitoring of patients during MRI procedures
(11). This information indicates that all patients
undergoing MRI examinations should be visually (e.g., using
a camera system) and/or verbally (e.g., intercom system)
monitored, and that patients who are sedated, anesthetized,
or are unable to communicate should be physiologically
monitored and supported by the appropriate means.
Injuries and fatalities have occurred in association with
MRI examinations. These may have been prevented with the
proper use of monitoring equipment and devices (3, 4, 11).
Notably, guidelines issued by the Joint Commission on
Accreditation of Healthcare Organizations (JCAHO) indicate
that patients receiving sedatives or anesthetics require
monitoring during administration and recovery from these
medications (12). Other professional organizations similarly
recommend the need to monitor certain patients using proper
equipment and techniques (5, 6, 8, 9, 13).
Why Monitor Body Temperature?
In human subjects, “deep” body or core temperature is
regulated between 36°C and 38°C by the hypothalamus and
continuously fluctuates due to diurnal, internal. as well as
external factors (14). Importantly, the regulation of body
temperature is suppressed by anesthesia and generally
results in the patients becoming hypothermic (15, 16).
Side-effects of a decrease in body temperature can range
from hypovolemia, myocardial ischemia, cardiac arrhythmia,
pulmonary edema, decreased cerebral blood flow in cases of
mild hypothermia, to mortality related to extreme
Additionally, some patients may experience malignant
hyperthermia, which is a rare life-threatening condition
that is usually triggered by exposure to certain drugs used
for general anesthesia. In susceptible individuals, these
drugs can induce a drastic and uncontrolled increase in
skeletal muscle oxidative metabolism, which overwhelms the
body's capacity to supply oxygen, remove carbon dioxide, and
regulate body temperature. Malignant hyperthermia can
eventually lead to circulatory collapse and death if not
quickly identified and treated.
The anesthesiologist or nurse
anesthetist may not be in the immediate proximity of the
patient during the MRI procedure due to the design of the MR
system. Therefore, it is imperative to continuously monitor
the body temperature and provide real time information to
the anesthesia healthcare professional. It is also important
that the measurement site has clinical relevance and a
relatively “fast” response time to any fluctuation in body
temperature because the anesthesiologist or nurse
anesthetist is unable to visualize the discoloration of the
patient skin in cases of sudden temperature changes.
Measuring Body Temperature
During an MRI
The accuracy and efficacy of the measurement of body
temperature has been a topic of discussion for many years
(14, 18-20). Temperature measurements in human subjects is
affected by, the following factors (14, 21):
-The site of measurement (e.g., skin, oral, esophagus,
rectal, pulmonary artery, hypothalamus, bladder, tympanic
membrane, axillary area).
-Environmental conditions (temperature and humidity).
-The measurement technique (e.g., mercury thermometer,
electronic thermometer, thermistor probe or catheter,
thermocouple-based probe, infrared radiation readers, fiber
The most accurate body
temperature is measured at the hypothalamus, but this site
is not accessible by any practical means. Therefore, a
“deep” body site that directly reflects the temperature
“sensed” by the hypothalamus will provide clinically
relevant information (14). For examples, sites that provide
high levels of accuracy and correlation to deep body
temperature are pulmonary artery blood, urinary bladder, the
esophagus, and rectum (18, 19, 22). However, the temporal
resolution for each site varies, which can dramatically
impact the ability to recognize clinically important changes
that may require prompt patient management (14, 18).
When monitoring temperature
during MRI, the decision on which body site to use should be
based on accuracy as well as accessibility. There may be
limitations on the type of equipment available for
temperature measurements in the MR system room (3, 8, 23).
For example, hard wire thermistor or thermocouple-based
sensors are prone to measurement errors due to
electromagnetic interference (EMI) and may introduce
artifacts in the MR images (3). Fiber optic sensors (i.e.,
fluoroptic thermometry) are optimally used to record
temperatures in the MRI environment because they safe and
unaffected by EMI (3).
In the MRI setting,
anesthesiologists, nurse anesthetists, and clinicians may be
feel that they are limited to measure “surface”
temperatures, such as those in the skin, axilla, and groin.
However, these temperature measurement sites are very
problematic insofar as they do not properly reflect “deep”
body temperature. Another option is to use minimially
invasive measurement techniques to record temperature in the
rectum or esophagus.
While a so-called “surface”
temperature site (i.e., skin, axilla, and groin) tends to be
used for temperature recordings during MRI mainly because of
the ease of obtaining the measurement with currently
available equipment, this method does not provide an
accurate representation of body temperature and is
susceptible to substantial variations and erroneous
information relative to the “deep” body temperature due to
the specific site selected for temperature probe placement,
patient movement, and environmental conditions (14, 19, 20)
Notably, recording skin or
surface temperature during MRI can be influenced by the
level of the patient’s perspiration due to RF heating and
the use of blankets or air circulation from the fan in the
bore of the MR system. Additionally, investigations have
demonstrated that peripheral vasoconstriction resulting from
skin surface cooling decreases the surface temperature
measurement without influencing the core or deep body
In contrast, core or “deep”
body temperature measurements require additional set up time
and are minimally invasive but provide a more accurate
representation of the body temperature (14). Two of the most
prevalent core temperature measurement sites used during MRI
procedures is the rectum and esophagus.
measurements are highly accurate and within 0.6oC of the
deep body temperature (14). The main drawback to this
temperature measurement site is associated with a lag or
delay in the temporal response to changing body temperature
due to the presence of thermal inertia from the intervening
tissues (i.e., between the rectum and hypothalamus). This
temporal delay may also be caused by the presence of feces
and poor blood supply in the rectum (14, 25). A clinical
investigation reported that the rectal temperature
substantially lagged in response to changes in body
temperature (25). The lack of temporal resolution can expose
the patient to a hypothermic or hyperthermic condition for
an extended period without being recognized by the
clinician. Also, special care must be taken when placing a
rectal temperature probe in neonatal or pediatric patient to
prevent perforation and infection (14, 25).
measurements provide a high level of accuracy and good
temporal correlation to body temperature due to the close
proximity to the aorta, a deep body site. (20). In addition
to the accuracy, the temperature recorded in the esophagus
is responsive to fluctuations in body temperature and
readily tracks changes compared to rectal or surface
temperature measurement sites (14, 25). The only caveat is
that the accuracy of measuring temperature in the esophagus
is directly linked to the proper positioning of the probe
(14, 19). Air flow in the trachea can impact the measured
temperature if the probe is not inserted deep enough into
the esophagus. The recommended placement of the sensor is in
the lower one-third of the esophagus for an accurate core
temperature measurement (14). Table 2 presents a comparison
of the measurement sites to monitor during MRI, with the
advantages and disadvantages.
Table 2. Comparison of
the measurement sites for temperature monitoring during MRI.
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