Comparison of Propofol With Pentobarbital/Midazolam/Fentanyl Sedation for Magnetic Resonance Imaging of the Brain in Children
Jay Pershad, Jim Wan and Doralina L. Anghelescu
Pediatrics 2007;120;e629-e636;
ABSTRACT
OBJECTIVE. Propofol and pentobarbital, alone or combined with other agents, are
frequently used to induce deep sedation in children for MRI. However, we are
unaware of a previous comparison of these 2 agents as part of a randomized,
controlled trial. We compared the recovery time of children after deep sedation
with single-agent propofol with a pentobarbital-based regimen for MRI and considered
additional variables of safety and efficacy.
METHODS. This prospective, randomized trial at a tertiary children’s hospital enrolled
60 patients 1 to 17 years old who required intravenous sedation for elective cranial
MRI. Patients were assigned randomly to receive a loading dose of propofol
followed by continuous intravenous infusion of propofol or to receive sequential
doses of midazolam, pentobarbital, and fentanyl until a modified Ramsay score of
_4 was attained. A nurse who was blind to group assignment assessed discharge
readiness (Aldrete score _ 8) and administered a follow-up questionnaire. We
compared recovery time, time to induction of sedation, total sedation time, quality
of imaging, number of repeat-image sequences, adverse events, caregiver satisfaction,
and time to return to presedation functional status.
RESULTS. The groups were similar in age, gender, race, American Society of Anesthesiology
physical status class, and frequency of cognitive impairment. No sedation
failure or significant adverse events were observed. Propofol offered significantly
shorter sedation induction time, recovery time, total sedation time, and
time to return to baseline functional status. Caregiver satisfaction scores were also
significantly higher in the patients in the propofol group.
CONCLUSIONS. Propofol permits faster onset and recovery than, and comparable efficacy
to, a pentobarbital/midazolam/fentanyl regimen for sedation of children for
OVER THE PAST decade, propofol-based sedation has
been used increasingly for procedures outside of
the traditional operating room setting.1–13 However,
there are few data from prospective, randomized, controlled
trials evaluating the use of single-agent propofol
to provide deep sedation of pediatric patients for MRI.14
The use of propofol with inhalational induction agents
or as the sole agent (total intravenous anesthesia) in
spontaneously breathing patients undergoing MRI has
been retrospectively studied.15–17 Pentobarbital, a shortacting
barbiturate, has a proven record of safety and
efficacy when used with midazolam or fentanyl for sedation
during pediatric diagnostic imaging.14,18–22 The
overall incidence of inadequate or failed sedation during
imaging procedures in children varies widely from 1% to
16%.21,23–25 We are not aware of any prospective, randomized
clinical trial comparing deep sedation with
propofol versus pentobarbital for pediatric MRI.
Propofol is an ultra–short-acting, nonbarbiturate,
nonbenzodiazepine sedative-hypnotic agent with an
arm-brain circulation time of 90 to 100 seconds. Sedation
is quickly induced by rapid distribution of the highly
lipophilic drug into the vessel-rich organs, including the
brain. Its rapid redistribution and clearance account for
its brief sedation effect and the need for repeated boluses
or continuous infusion to maintain the level of anesthesia
and sedation.26–28 Propofol induces dose-dependant
central nervous system depression. At the recommended
dose for induction in children 3 to 12 years old (2.5–3
mg/kg), a 21% incidence of transient apnea has been
reported.29 However, sedation regimens during imaging
procedures require lower doses and are associated with a
lower overall incidence of hypoxia or respiratory depression,
ranging from 0% to 10%.14,15,30 At subhypnotic
doses, propofol induces sedation, amnesia, and antiemetic
activity.31 The rapid titrability, brief pharmacologic
effect, and maintenance of spontaneous ventilation
make intravenous propofol an ideal agent for deep sedation
during pediatric MRI.
At our institution, pediatric patients are sedated for
diagnostic imaging with intravenous propofol or pentobarbital/
midazolam/fentanyl regimens. Pentobarbitalbased
regimens are usually used for MRI, whereas
propofol is preferred for the shorter-duration computed
tomography studies. All sedation in the radiology suite at
our institution is performed by a radiology sedation service
that is staffed and supervised exclusively by boardcertified
pediatric emergency physicians.32
The primary objective of this study was to compare
the recovery time (RT) after sedation with propofol versus
a pentobarbital-based regimen for cranial MRI studies
in children. Secondary outcome measures were induction
time (IT), total sedation time (TST), time to
return to baseline (TTB; presedation) functional status,
number of repeat imaging sequences, quality of images
obtained, caregiver satisfaction with sedation, and frequency
of immediate and delayed adverse events.
MATERIALS AND METHODS
Patients
Our study was a randomized, prospective, partially
blinded comparative trial of patients 1 to 17 years of age
who were scheduled for elective cranial MRI and who
required sedation. The study was conducted in the department
of radiology at an urban, tertiary-level pediatric
facility.
We excluded patients whose American Society of Anesthesiology
(ASA) physical status class was _3, those
requiring diagnostic imaging for trauma, and those for
whom any of the agents investigated were contraindicated.
A convenience sample of eligible patients was
given the opportunity to participate in this study, based
on the availability of the principal investigator. Our institutional
review board approved the study. Informed
consent was obtained from patients, parents, or guardians,
as appropriate, and Health Insurance Portability
and Accountability Act regulations were followed.
Sedation Protocol
Patients were assigned randomly to 1 of 2 groups by
using the method of randomly permuted blocks of size
10.33 The random allocation sequence was generated by
a biostatistician (Dr Wan) and provided in sealed numbered
envelopes. The sequence was concealed from the
sedating physician, until intervention was assigned. The
principal investigator enrolled participants and assigned
participants to 1 of 2 groups. Parents were present during
induction and recovery. Patients in the pentobarbital
group received midazolam, pentobarbital, and fentanyl
in sequential doses until the desired level of sedation was
achieved. Midazolam (0.1 mg/kg) was administered intravenously
up to a maximum dose of 5 mg, and pentobarbital
(2 mg/kg) was then given intravenously. Additional
doses of 1 mg/kg pentobarbital were then
administered until the desired level of sedation was
achieved, up to a maximum of 6 mg/kg. The cumulative
dose of pentobarbital was limited to 200 mg. If adequate
sedation was not achieved, fentanyl (1 _g/kg) was administered
intravenously, up to a maximum dose of 100_g.
Patients in the propofol group received an initial dose
of 0.5 mg/kg lidocaine mixed in the same syringe, to
decrease the pain associated with injection of intravenous
propofol. A loading dose of intravenous propofol
was administered in 1 mg/kg aliquots, each administered
over a period of 60 seconds, until loss of eyelid reflex was
observed. Supplemental doses of 0.5 mg/kg were administered
until the desired level of sedation was attained. A
maintenance infusion was initiated at 6 mg/kg per hour.
If the patient moved before or during the scan, addtional 0.5 mg/kg
propofol boluses were administered
and the infusion rate was incrementally increased by
10%, up to a maximum of 15 mg/kg per hour.
In accordance with our institution’s sedation policy,
all patients received continuous heart rate, pulse oximetry,
and nasal capnography monitoring, and respiratory
rate and blood pressure were assessed every 5 minutes.
Patients received preoxygenation with blow-by oxygen
via facemask to maintain oxygen saturation of _95%. A
registered nurse with specialized training in sedation
monitored the patient before, during, and after the procedure,
until the patient was ready for discharge. Because
MRI necessitated remote monitoring, close vigilance
was provided throughout the scanning procedure.
An attending pediatric emergency medicine physician
credentialed by our institution to provide procedural
sedation was present at all times to monitor the patient
and provide immediate intervention as needed.
While sedated, patients were closely observed for
signs of upper-airway obstruction, such as snoring, stridor,
decreasing hemoglobin oxygen saturation, loss of
exhaled carbon dioxide, or progressive hypercapnia, as
detected by the end-tidal capnographic wave form. Airway
rescue measures, including airway manipulation,
suction, and insertion of a nasal airway, were used sequentially
as needed. If the patient’s ventilatory status or
oxygenation did not improve, assisted ventilation was
initiated, and the procedure was aborted according to
the decision of the principal investigator.
After completion of the scans, a registered nurse not
associated with the study who was blind to the type of
medication received evaluated discharge readiness.
Standard discharge criteria (Aldrete score)34 were used.
Recovery was graded at 5-minute intervals. Patients met
discharge criteria when they reached an Aldrete score of
_8 or reached a score within 2 points of their presedation
score.
Assessment of Sedation Efficacy and Adverse Events
Sedation was considered efficacious if the patient lost
consciousness, underwent the procedure without movement,
and maintained spontaneous, adequate respiratory
effort. We used the Ramsay scale35 to measure the
level of sedation. Our goal was to achieve a level of _4
on the Ramsay scale.
Failure to achieve adequate sedation (ie, patient
awakened or moved, interfering with completion of the
MRI) despite maximal doses was considered a failure of
the sedation regimen, and the procedure was rescheduled.
Sedation was also considered to have failed if the
procedure was aborted because of a significant adverse
event.31
Possible “major” adverse events during sedation include
hypotension, hypoxemia, emesis, agitation, apnea,
respiratory depression, laryngospasm, and bradycardia.
Hypotension was defined as systolic blood pressure _70
plus twice the patient’s age in years, associated with
altered peripheral perfusion (delayed capillary refill
time). Hypotension was treated with a 20 mL/kg intravenous
bolus of crystalloids and a 10% reduction in the
propofol infusion rate. Hypoxemia was defined as a
pulse oximetry value _90% and prompted immediate
intervention. Emesis was defined as presence of stomach
contents in the pharynx, at any time after administration
of the sedation drugs. Agitation was defined as uncontrollable
distress or inconsolability despite parental presence.
Apnea was defined as cessation of respiration for
_20 seconds. Bradycardia was defined as a heart rate
below 50 beats per minute. Laryngospasm was identified
by the occurrence of airway obstruction or stridor with a
decline in pulse oximetry readings that was not relieved
by airway manipulation, suction and insertion of oral or
nasal airway, and required assisted ventilation or neuromuscular
blockade to achieve adequate ventilation.
“Immediate” adverse events were those that occurred
during sedation or before discharge. Delayed adverse
events were adverse effects that occurred after discharge,
as noted during the follow-up satisfaction survey. We
did not record “minor” adverse events that were selflimited
and typically associated with administration of
parenteral sedatives. These include pain or discomfort
during injection (usually observed with propofol), transient
myoclonus (usually noted with propofol), and facial
pruritis with fentanyl administration.
Assessment of Other Variables
The following data were collected for each patient: age,
gender, indication for diagnostic study, presence or absence
of cognitive impairment, sedation IT, scan time,
RT, TST, sedation efficacy or failure, frequency and timing
of adverse effects, imaging efficacy (quality of MRI
scan), and satisfaction of the caregiver with procedural
sedation. IT was defined as the time from initial administration
of the drug to achievement of sedation adequate
to perform the MRI. Scan time was defined as the
length of time between the patient’s placement on the
MRI table and completion of the imaging sequences. RT
was defined as the time that elapsed between scan completion
and meeting of discharge criteria. TST was defined
as the time between administration of the first dose
of drug and patient readiness for discharge. Quality of
images was rated on a 5-point Likert scale based on the
presence or absence of motion artifact, by an independent
radiologist, blind to the identity of the patient and
the sedation regimen. Scans were assigned quality ratings
of 1 (poor) through 5 (excellent). An independent
nurse blind to the sedation regimen made a follow-up
telephone call 24 to 48 hours after discharge to determine
the time at which the child returned to the baseline
level of function and whether delayed adverse events
were observed. During this telephone call, parents or
caregivers were asked to assign a score on a 5-point
Likert scale (5 being extremely satisfied and 1 being not
at all satisfied) assessing their satisfaction with the overall
sedation process.
Data Analysis
The primary outcome measure was RT. Secondary outcome
measures were IT, TST, quality of imaging, number
of repeat image sequences, frequency of immediate
and delayed adverse events, sedation success or failure,
caregiver satisfaction, and caregiver report of TTB. According
to Kienstra et al21 and Mason et al,20 the standard
deviation for the RT in the pentobarbital group was 32
minutes. From Hasan et al,30 the standard deviation for
the RT in the propofol group was 21 minutes. Assuming
a probability (P) of type I error of .05 and a power of
80%, the required sample size to detect a 20 minute
difference in RT was 30 subjects for each group. The
2-sample t test was used to test the difference in RT
between the 2 groups. For secondary outcomes, categorical
variables with small sample size, such as the frequency
of adverse events and sedation failures, were
compared between the 2 groups using Fisher’s exact test.
The Mantel 1-degree-of-freedom _2 test was used to
compare the Likert-scale variables. All analyses were
performed by using by SAS 9.1.3 statistical software
(SAS Institute Inc Cary, NC).
RESULTS
Sixty patients were assigned randomly to 1 of 2 groups
(Fig 1). The groups were similar in age, gender, race,
American Society of Anesthesiology physical status class,
and proportion of patients with cognitive impairment
(Table 1). The mean total dose of each drug is listed in
Table 2. No sedation failures or significant adverse
events were recorded. RT, sedation IT, TST, TTB functional
status, and caregiver satisfaction scores significantly
favored propofol over pentobarbital. No significant
differences were observed between the groups in
imaging quality or in the number of repeat images (Tables
3 and 4).
The adverse events that occurred were relatively minor.
We observed 11 immediate adverse events, 8 in the
propofol group, and 3 in the pentobarbital group. The
propofol-related immediate adverse events were transient
decreased blood pressure without signs of compromised
peripheral perfusion in 4 cases and respiratory
depression in 4 cases. The 4 cases of respiratory depression
occurred during induction. Two children developed
partial airway obstruction without desaturation, which
corrected with airway manipulation including chin lift
maneuver. Two patients experienced a decrease of oxygen
saturation into the 80s and 70s, respectively, that
lasted for _1 minute. One subject responded to airway
manipulation, readjustment of oxygen mask, and suction.
The other patient required brief (_60 seconds)
assisted ventilation with a bag mask and insertion of
nasal airway, after which adequate spontaneous ventilation
was observed. The nasal airway was maintained
for the duration of the scan. None of these cases received
tracheal intubation or escalation of care to warrant
aborting the procedure. The remainder of the scanning
procedures in these patients was uneventful. Pentobarbital
sedation was associated with 3 immediate adverse
events: 1 episode of transient decreased blood pressure
and 2 cases of emergence agitation. Seven delayed adverse
events were noted, all in the pentobarbital group.
These comprised 6 cases of prolonged sedation and 1
case of delayed agitation.
DISCUSSION
Our results demonstrate that propofol provided significantly
shorter recovery, sedation induction, TSTs, TTB
functional status, and better caregiver satisfaction scores
compared with a pentobarbital/midazolam/fentanyl regimen.
The differences in mean induction, recovery and
TSTs were 8, 17, and 20 minutes, respectively, in favor of
propofol. When extrapolated to multiple sedations, we
believe that these differences have clinical significance
and pharmacoeconomic impact by optimizing the use of
the MRI scanner. In a previous prospective trial, Bloomfield
et al14 noted propofol to be associated with a shorter
time to arousal and time to discharge then pentobarbital.
Our trial differed from theirs in that all participants were
assigned randomly to the treatment groups. In addition,
the nurse responsible for monitoring recovery and discharge
and for conducting the telephone follow-up in
our study was blind to the type of agent received. Although
subjects in both studies were preoxygenated,
end-tidal carbon dioxide monitoring was not part of the
protocol used by Bloomfield et al. In addition, pentobarbital
was used as a single agent in doses higher than
those used in our study (maximum total dose: 7.5 vs 6
mg/kg), and the details of pentobarbital dosing and the
incidence of adverse events were not described.
Our study has several limitations. This was a convenience
sample of eligible patients based on the availability
of the principal investigator. The physician investigator
responsible for administration of propofol and
supervision of procedural sedation in both groups was
not blind to the agent received. Although this factor may
have introduced some bias, the presence of the investigator
ensured strict adherence to the sedation protocol.
The fact that we restricted enrollment to patients scheduled
exclusively for cranial MRI may limit extrapolation
of our results to MRI studies of other body parts. However,
this restriction was designed to reduce variation in
scan time among the study subjects.
It could be argued that the use of midazolam as an
adjunct to pentobarbital may have prolonged the RT.20
Our institution currently leaves the choice of sedative
agent for MRI to the discretion of the practicing physician.
For more than a decade, the practice in our radiology
department has been to premedicate with midazolam.
Because of the success of this experience,
midazolam sedation was included in our trial in an attempt
to reduce the total dose of pentobarbital, an intermediate-
acting barbiturate.
The maximum allowed infusion rate of 15 mg/kg per
hour of propofol in our protocol was higher than the 9 to
10 mg/kg per hour cited in the literature, although our
starting rate of 6 mg/kg per hour is a standard approach.
14,15 Also, subsequent boluses for patient movement
during the scanning procedure were administered
in 0.5 mg/kg aliquots, with a 10% incremental adjustment
in drip rate. This was lower than the 1 to 2 mg/kg
doses of propofol for subsequent boluses used in previous
studies; therefore, our increments were more conservative.
14,15
The cumulative maximum dose of pentobarbital in
our study was 6 mg/kg (200 mg). This was consistent
with the dose used in 2 previous studies22,24 and higher
than the 5 mg/kg used in 2 other trials.21,36 In contrast, 1
previous study used a maximum dose of 6.5 mg/kg of
pentobarbital.37 Furthermore, the method of administration
of pentobarbital in our study was an initial bolus of
2 mg/kg followed by additional aliquots of 1 mg/kg until
adequate sedation was achieved. Previous studies used 2
mg/kg boluses for additional dosing.22,24 Others used a
smaller dose for subsequent boluses ranging from 1 to 2
mg/kg aliquots of pentobarbital.20,21 It is possible that the
relatively smaller incremental doses of pentobarbital
used in our study may have led to a bias in favor of the
propofol group.
Overall, the difference in frequency of adverse events
between the 2 groups in our study was not statistically
significant. However, given the small numbers, we were
unable to exclude the possibility of a type II error. Adverse
events of respiratory depression during induction
and hypotension, observed with propofol administration
in our study were similar to those previously reported.
14,15,29 We noted transient respiratory depression in 4
(13.3%) of 30 patients in the propofol group versus 0
(0%) of 30 in the pentobarbital group. This difference
was not statistically significant (P _ .11). The relatively
higher incidence of respiratory adverse events in the
propofol group highlights the importance of having a
physician trained in advanced airway management immediately
available. The pentobarbital regimen was associated
with prolonged sedation in 6 patients (20%)
and emergence agitation in 2 patients (6.7%). One subject
experienced delayed agitation after discharge from
the hospital. The incidence of emergence agitation noted
in our study is consistent with the incidence reported in
the literature. The incidence of paradoxical hyperactivity
for all drug regimens, including pentobarbital, as reported
by Rubin et al38 was 1.8%. Emergence agitation
noted with the use of pentobarbital alone varies greatly
between studies: 0% in Mason et al19 in 2004, 1.2% in
Karian et al,23 1.5% in Mason et al,20 7% in Greenberg et
al,24 12% in Kienstra et al,21 and 14% by Malviya et al.36
Furthermore, the incidence of paradoxical hyperactivity
with pentobarbital was comparable when considered
with and without adjunctive midazolam (1.6% vs
1.5%).20 The report of prolonged sedation in our study,
was based on subjective responses obtained from the
parents or caregivers, on the 24- to 48-hour postdischarge
follow-up survey. This may have led to some bias
against the subjects assigned to the pentobarbital medication
regimen.
CONCLUSIONS
Our results highlight the favorable induction and recovery
profile of propofol sedation, while showing comparable
efficacy to a pentobarbital-based regimen in pediatric
patients undergoing cranial MRI. Although
absolute reduction in induction and RT were relatively
small, when extrapolated to multiple encounters for a
busy sedation service, the time savings and potential
economic impact may be significant.
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