●●●
A Novel Vibrotactile Display to Improve the Performance
of Anesthesiologists in a Simulated Critical Incident
Simon Ford, MB ChB, FRCA*
Jeremy Daniels, BASc, EIT*
Joanne Lim, MASc*
Valentyna Koval, MD†
Guy Dumont, PhD, P.Eng‡
Stephan K. W. Schwarz, MD,
PhD, FRCPC*
J. Mark Ansermino, MBBCh,
MSc(Inf), FFA*
BACKGROUND: Current methods of information transfer in the operating room
between monitor and anesthesiologist rely on visual and auditory modalities.
These modalities can easily become overloaded in a high cognitive workload
situation, such as in a critical incident. The use of vibrotactile communication has
been shown to improve information transfer in other high cognitive workload
environments such as aviation. We designed a novel waist-mounted vibrotactile
display to be worn by the anesthesiologist to test if a vibrotactile display could
improve the clinical response time to begin treating a simulated case of anaphylaxis
when compared with a group using traditional information displays. In addition,
we evaluated differences in situational awareness (SA) between the two groups.
METHODS: Twenty-four volunteer anesthesiologists were randomized to diagnose
and treat a simulated case of anaphylaxis using the vibrotactile display and
standard monitoring (vibrotactile display group) or standard monitoring alone
(control group). The time taken to administer epinephrine was measured, and
objective post hoc analysis of participant SA was performed.
RESULTS: Participants in the vibrotactile group took 4.08 min (95% CI
1.22) to
deliver definitive treatment compared with 7.21 min (95% CI
2.07) for the control
group (P  0.05). Despite the reduced time to treatment, no improvement in SA
was measured.
CONCLUSION: Our study provides evidence that vibrotactile communication can
reduce response time to critical incidents.
(Anesth Analg 2008;X:●●●–●●●)
In the field of anesthesiology, the technical ability to
measure clinical variables has advanced at a greater
pace than the ability to effectively display these vari-
ables. Clinical monitoring devices provide the anesthe-
siologist with essential information about a patient’s
physiological status. Information must be displayed in
an intuitive and comprehensible way to maximize
transfer to the anesthesiologist and optimize situ-
ational awareness (SA). SA is an accurate knowledge
of the patient’s measured physiological variables,
comprehension of those variables in a clinical context,
and a projection of the patient’s condition into the
immediate future.1 Clinical interventions and deci-
sions are based on this knowledge; therefore, patient
safety can be improved if SA is maximized.
Humans have a finite and limited capacity for
information transfer. The human visual and auditory
modalities can only reliably differentiate 6–7 stimuli
each at any given time.2 This ability is further reduced
when high cognitive demand is present, as is com-
monly the case in anesthesiology.3 If the main senses
of information transfer, vision and hearing, are al-
ready fully saturated, as in an emergency situation,
information delivered via these saturated pathways
may not be reliably received. Therefore, an alternative
sensory route may prove beneficial.
Vibrotactile stimulation is an effective method of
communication, which can be used to substitute for,
or augment another sensory modality.4–6 Vibrotac-
tile communication can occur without relying on or
disturbing visual or auditory information pathways.
We have shown previously that vibrotactile commu-
nication provides greater accuracy in recognizing an
array of physiologically meaningful alarms compared
with standard auditory communication.7 Vibrotactile
stimulation can serve to transmit information, but
may also facilitate attention switching among moni-
tored variables.
We designed and built a waist-mounted vibrotac-
tile display to facilitate physiological information
From the *Department of Anesthesiology, Pharmacology and
Therapeutics and †Centre of Excellence for Surgical Education and
Innovation, Vancouver General Hospital, and ‡Department of Elec-
trical and Computer Engineering, University of British Columbia,
Vancouver, British Columbia, Canada.
Accepted for publication November 20, 2007.
Supported by a Collaborative Health Research Project grant
from the Canadian Institutes of Health Research and the Natural
Sciences and Engineering Research Council of Canada. Dr. Schwarz
is recipient of the 2006 Canadian Anesthesiologists’ Society (CAS)
Research Award and the 2006 CAS/Abbott Laboratories Ltd. Career
Scientist Award in Anesthesia.
Address correspondence and reprint requests to Simon Ford,
Department of Anesthesia, British Columbia Children’s Hospital.
4480 Oak St., Vancouver, BC, V6H 3V4, Canada. Address e-mail to
smford1@gmail.com.
Copyright © 2008 International Anesthesia Research Society
DOI: 10.1213/ane.0b013e318163f7c2
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transfer to the anesthesiologist. We conducted a pro-
spective randomized trial using a human patient
simulator to assess whether vibrotactile communica-
tion has the potential to improve an anesthesiologist’s
response time to a critical incident. We designed a
scenario containing a critical incident of anaphylaxis
to test the hypothesis that the group using the vibro-
tactile display would administer epinephrine signifi-
cantly earlier than the control group. In addition, we
sought to evaluate differences in SA between the two
groups.
METHODS
Participant Recruitment
With institutional Clinical Research Ethics Board
approval, we conducted a prospective, randomized,
parallel-group, single-center (Centre of Excellence for
Surgical Education and Innovation, Vancouver Gen-
eral Hospital, Vancouver, B.C., Canada) trial to test
whether our vibrotactile display would reduce the
response time of an anesthesiologist to diagnose and
treat a simulated critical incident of anaphylaxis. After
obtaining written informed consent, 24 volunteers
were randomly assigned to use either the vibrotactile
display combined with standard monitoring8 (vibro-
tactile display group) or standard monitoring alone
(control group) during the simulated scenario. The
study included male and female staff anesthesiolo-
gists, anesthesiology fellows, and 5th year anesthesi-
ology residents with a minimum of 4 yr clinical
anesthesia experience. Volunteers were excluded if
they had a history of back surgery resulting in a
significant sensory deficit, or significant cardiovascu-
lar disease, including poorly controlled hypertension.
Participants were randomized into two equal groups
of 12 using a Random Block Size Method (Statsdirect
Statistical Software, Statsdirect.Ltd., Manchester, UK).
Study Procedure
Participants undertook the simulated scenario indi-
vidually lasting approximately 30 min. All volunteers
underwent a short period of familiarization with a
high fidelity human patient simulator mannequin
(HPS-245, METI Corp., FL), drug delivery system and
anesthetic machine (S/5™ Anesthesia Delivery Unit,
Datex-Ohmeda Inc., Madison, WI). The vibrotactile
group received only a further short period of training
about the vibrotactile display to ensure comfort and
stimulus recognition. This period of training lasted 5
min and ensured each participant could correctly
recognize each potential pattern. Each participant had
to correctly identify the meaning of all four stimuli
positions given in a random order before qualifying to
start the scenario. All participants were given an
introductory sheet with a brief medical history about
the “patient” and the type of surgery scheduled
(Appendix 1: Scenario Patient History; available at
www.anesthesia-analgesia.org).
Simulated Scenario
To initiate the scenario, participants induced anes-
thesia, intubated the trachea of the mannequin, and
maintained inhaled anesthesia using recognized mini-
mum standards of monitoring.8 Auditory alarms were
set to the default limits of the Aestiva S/5 (Anesthesia
Delivery Unit, Datex-Ohmeda Inc.) for both groups.
Participants were permitted to change these limits to
coincide with their standard practice. The critical
incident of anaphylaxis commenced after a postinduc-
tion steady-state. Each stage of the critical incident
had a preset duration, and automatically progressed
to a more severe state unless epinephrine 1
g/kg or
more was given IV (Appendix 2: Scenario Stage Pro-
gression, available at www.anesthesia-analgesia.org).
The administration of epinephrine was sensed via a
bar code on the syringe, which triggered the recovery
phase of the simulated scenario and provided a pre-
cise time for drug administration. The time taken from
the start of the critical incident to the administration of
epinephrine was measured for each participant. Our
primary hypothesis was that the group using the
vibrotactile display would administer epinephrine
20% sooner than the control group. We considered a
20% difference in response time to be a clinically
significant benefit that could improve patient safety.
We deliberately chose anaphylaxis as our critical
incident instead of a pure respiratory scenario (e.g.,
pneumothorax or pulmonary embolus) to reduce the
risk of bias in the vibrotactile display group, as the
display transmitted only respiratory-related informa-
tion. We elected not to use a sham vibrotactile display
(an inactivated vibrotactile belt) in the control group
in case participants misunderstood the instructions
and erroneously relied on the display to receive infor-
mation. We aimed to compare our vibrotactile display
with current real world anesthesia practice and there-
fore tried to make the control group conditions as
authentic as possible.
Vibrotactile Display
Our vibrotactile display was designed to maximize
sensory perception at the skin and function in a
simulated clinical setting. Vibrating motors (“tactors;”
FM 37E flat coreless vibrating motors, Sanyo, Osaka,
Japan) were used to stimulate Pacinian sensory cor-
puscles under the skin close to their optimum re-
sponse range of approximately 200 Hz.9 These tactors
were attached to the vibrotactile display using mov-
able pockets to ensure common tactor positions for
each participant (Figs. 1 and 2). The vibrotactile dis-
play itself was developed from a commercially available
tool belt (Mastercraft ClipTech 27 tool belt, Canadian
Tire, Guelph, Ontario, Canada). We used a belt design
as information transfer at the waist has been shown to
be highly accurate10 and also acceptable to clinicians.11
Our vibrotactile display used four tactors to ensure
simple patterns for participants to comprehend. This
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design was within the information transfer limits for
tactile communication of 2.65 bits, described by
Cholewiak et al.10 The simple design and stimulation
pattern of the vibrotactile display was chosen to avoid
participant distraction during the scenario and maxi-
mize their opportunity for stimulus identification and
comprehension of the meaning of that stimulus.
The tactor stimulation pattern was controlled by a
personal computer interfaced to a controller board
(Phidget interface kit 0/16/16, Phidgets Inc., Calgary,
Canada). It delivered a stimulus of two periods of
vibration lasting 500 ms separated by 500 ms. Stimuli
were received at only one tactor at any given time. The
tactors on the participants’ right sides signaled a
change in peak airway pressure, whereas the tactors
on the left side signaled a change in minute volume
ventilation. A stimulus on the anterior tactors repre-
sented a 25% increase in a variable’s value. A stimulus
on the posterior tactors represented a 25% decrease in
a variable’s value. The postinduction baseline value
for peak airway pressure was 16 cm H2O and 7.2 L for
minute volume. Further vibrotactile stimuli were re-
ceived after each successive 25% change in peak
airway pressure or minute volume.
Our secondary hypothesis was that the group using
the vibrotactile display would score more correct an-
swers to SA question probes than the control group. To
test this hypothesis, we developed a novel technique to
objectively measure participants SA based on the Situa-
tion Awareness Global Assessment Test described by
Endsley.12 This technique requires stopping the simula-
tion scenario to deliver the SA question probes and then
recommence the scenario. We adapted this technique by
applying the stops and question probes in a post hoc
manner while participants reviewed a video recording of
their scenario. The review video showed the monitor
display of physiological variables and the participants in
the simulation room undergoing the scenario, using a split
screen format. The video was stopped, and physiological
data disappeared from view while participants answered
the SA questions. Our aim was to maintain an objective
measure of SA while avoiding interruption of the scenario
to allow accurate timing of epinephrine administration.
SA question probes were designed to test a partici-
pant’s knowledge on three levels.1 The first level exam-
ined the participant’s knowledge of the displayed
Figure 1. Vibrotactile display. Posterior right tactor visible,
posterior left tactor in movable pocket.
Figure 2. Position of tactors on the vibrotac-
tile display.
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variables, the second level tests comprehension of vari-
ables forming a clinical picture of the patient’s condition,
and the third level tests prediction of the patient’s status
in the near future. We designed a decision pathway the
clinician might follow to make the correct diagnosis of
anaphylaxis. This pathway identified knowledge of
variables, comprehension, and predictions the par-
ticipant would need to make to formulate the cor-
rect diagnosis and treatment. We targeted our SA
question probes to test the information outlined in
our decision pathway. Thirty-five questions (Ap-
pendix 3: Situational Awareness Questions, available at
www.anesthesia-analgesia.org) were delivered over six
stops. We used six stops to allow us to gain as much
information as possible about SA while avoiding too
many interruptions to the video.We allowed 1minute of
continuous video between each stop to allow partici-
pants to reorient themselves within the scenario. On
completion of the study, participant responses were
reviewed in conjunction with the video and marked
correct or incorrect. Level one responses were allowed a
margin of error of 10% for heart rate and peak airway
pressure values and 2% for oxygen saturation values,
while still being marked correct.
Usability Questionnaire
Participants wearing the vibrotactile display
were asked to complete an analog usability ques-
tionnaire based on the work of Lewis,13 but modi-
fied for our purposes (Appendix 4; available at
www.anesthesia-analgesia.org). The questionnaire
used in this study had been used in a previous
vibrotactile usability study.11 We used this tool to
gain participants’ opinions on the usability of our
vibrotactile display generating scores ranging from
1 to 7 along a visual analog scale, 1 being strong like
and 7 being strong dislike.
Statistical Analysis
We hypothesized that the time to epinephrine admin-
istration would be 20% faster in the vibrotactile display
group than the control group. In an a priori power
analysis, we calculated that we would require 12 partici-
pants in each group to achieve our goals of 80% study
power (
0.2) and 5% significance (
0.05). The time
taken from the start of the critical incident to epinephrine
administration for the vibrotactile and control groups
was analyzed using an unpaired Student’s t-test. The SA
question probe answers were compared between the
groups for each question using Fisher’s exact test. A
Bonferroni correction for multiple comparisons was ap-
plied as appropriate. Peirce’s criteria was used to test for
and exclude statistical outliers.14
RESULTS
Two participants were excluded from analysis of
the vibrotactile display group due to a technical
failure of the mannequin (n
1) and failure of the
vibrotactile display to provide the stimulus (n
1).
One participant in the control group was withdrawn
from analysis due to failure of the scenario. The
demographics of the remaining 21 participants (vi-
brotactile display group, n
10; control group, n

11) with respect to seniority, previous simulator
experience, clinical anaphylaxis experience, and
prior exposure to the anesthetic machine are shown
in Table 1.
One extreme outlier in time taken to administer
epinephrine was excluded from analysis in the vibro-
tactile display group. This result lay 2.5 standard
deviations (sd) from the group mean and met Peirce’s
criteria for exclusion.14
Participants in the vibrotactile display group deliv-
ered the definitive treatment of epinephrine signifi-
cantly earlier in the scenario than those in the control
group (vibrotactile display group, 4.08  1.22 min;
control group, 7.22  2.07 min (mean  95% CI, P 
0.05; Fig. 3). There was no difference in SA question
probe responses between the vibrotactile and control
groups. Figure 4 shows the percentage of correct
answers for the eight question probes requiring spe-
cific knowledge of airway variables.
Ten participants from the vibrotactile display group
completed the usability questionnaire. The two par-
ticipants who experienced scenario failure or vibrotac-
tile display failure were excluded from the usability
review. Overall, the study volunteers found the vibro-
tactile belt comfortable and easy to use, and could
envision potential clinical benefit (Fig. 5).
DISCUSSION
In a prospective, randomized, controlled study, we
have demonstrated that a vibrotactile display can
reduce the time to epinephrine administration when
Table 1. Demographics of Vibrotactile and Control Groups
Group
Previous
simulator
experience
Previous
experience of
anaphylaxis
Prior exposure to
IDENTICAL
anesthetic machine Sex Grade
Vibrotactile
N
10
6 5 5 Male 8
Female 2
Staff 7
Fellow 1
Resident 2
Nonvibrotactile
N
11
5 5 5 Male 9
Female 2
Staff 8
Fellow 1
Resident 2
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F3
F4
F5
4 A Tactile Display to Aid Anesthesiologists ANESTHESIA & ANALGESIA

treating a simulated case of anaphylaxis. The vibro-
tactile display enhanced treatment response time by
providing information about a patient’s airway pres-
sure and minute volume with a vibratory signal easily
detected and its meaning easily understood.
Vibrotactile displays have several potential advan-
tages compared with traditional visual and auditory
displays. For example, unlike visual displays, tactile
displays do not require visual attention to be diverted
from the patient, and, unlike audio alarm systems,
they do not pollute an already noisy operating room
environment.15 Vibrotactile communication has the
ability to attract attention and convey information
with reduced potential interference to the other mo-
dalities of hearing and vision.16,17 However, modality
interaction observed in the laboratory setting may be
very different from those observed in the clinical
setting of the operating room. The tactile modality has
communication attributes that make it suitable for the
operating room environment: it is personal (sensed
only by the person wearing it), obligatory (unable to
prevent stimulation unless device removed), and does
not interrupt other peoples work pattern.18 Visual
displays permit fixation on one variable to the detri-
ment of the patient’s general condition.19 Therefore, a
display system that combines both tactile and visual
input may reduce visual fixation by providing a
second source of information.
Our study may have been biased by warning partici-
pants of one group about airway/ventilation variables
using the vibrotactile display. The presence of our dis-
play may have indicated a diagnosis partly defined by
alteration of airway variables such as anaphylaxis, pneu-
mothorax, or bronchospasm. However, the vibrotactile
display variables of peak airway pressure and minute
volume alone would not immediately alert a participant
to an impending scenario of anaphylaxis.
Participants in the control group commonly fo-
cused on treating airway difficulties leading to de-
layed epinephrine administration. This paradoxical
Figure 3. Time to administer epinephrine,
vibrotactile display, and control groups.
Data are presented as mean, 95% CI, and
range in brackets.
Figure 4. Correct responses to respiratory
related situational awareness questions
probes. No statistical difference was dem-
onstrated between the responses of the two
groups.
Figure 5. Usability Questionnaire responses
for each question. Data are presented as
mean  sd.
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observation may be explained by observing the timing
of the information delivery about peak airway pres-
sure to the two groups. The initial stage of the scenario
mimicked a dehydrated patient under anesthesia, as is
often seen in patients who have undergone bowel
preparation. As the critical incident progressed, the
hypotension became more pronounced and broncho-
spasm evolved. Participants in the vibrotactile display
group were notified of an increase in peak airway
pressure every time there was a 25% change. The
information was transmitted to the vibrotactile dis-
play participants without breaking their concentra-
tion, allowing them to treat the coexistent hypotension
and tachycardia. This steady increase in peak airway
pressure could be placed into the clinical context of
cardiovascular changes to reach the diagnosis of ana-
phylaxis. The treatment of the scenario with epineph-
rine does not confirm the correct diagnosis was made
by subjects. The drug may have been given purely for
cardiovascular/respiratory supportive reasons. How-
ever, all subjects underwent a similar scenario gov-
erned by a time-controlled stage progression. This
suggests that some diagnostic advantage occurred in
the vibrotactile group, otherwise supportive treatment
would be expected to be administered at similar times
in both groups. Participants in the control group often
only noticed an increase in peak airway pressure
when the alarm sounded at 25 cm H2O, although the
steadily increasing value was displayed visually on
the monitor throughout the scenario. These partici-
pants had no knowledge of the rate of change of the
variable, whether it was a sudden event or a progres-
sive trend. At this point, control participants changed
focus from treating cardiovascular problems to the
more immediate problem of bronchospasm manage-
ment. This may have delayed the recognition of the
intended diagnosis of anaphylaxis and administration
of epinephrine.
The observation that SA question probes showed
no difference between the two groups is counterintui-
tive. It is possible the post hoc method of SA analysis
may not be a reliable tool. Short-term memory abilities
of participants may have affected accuracy during post
hoc questioning. We attempted to minimize this effect
by presenting participants with a video of the monitor
display to refresh their memory until the point of
questioning. More importantly, participants may have
found it difficult to remember at what point they
became aware of new facts when answering questions
in the post hoc video review. Reviewing the video with
knowledge of what happened in the scenario may
have increased the number of correct SA responses,
masking the real difference between the two groups. A
difference may have been shown if the question
probes had been administered in real-time as is clas-
sically described.12 Also, the nonvalidated question
probes and small sample size may not have made the
test sensitive enough to show a difference in SA. This
underscores the need for further research into vali-
dated question probes for the objective measurement
of SA in medical simulation environments.
The fidelity of the simulation to the real-life
environment was an important consideration. We
believe that our simulated scenario provided a good
representation of anaphylaxis for several reasons.
First, 80% of participants made a correct diagnosis
and treated the simulated anaphylaxis. Second, the
feedback obtained from participants (with previous
clinical experience of anaphylaxis) indicated that
the simulation was realistic.
The vibrotactile display provided a benefit to clini-
cal decision-making and received favorable responses
from participants via usability questionnaires in a
simulator-based study. The display is a prototype that
will require modification, including wireless capabil-
ity, before being introduced to the operating room.
However, our results from the usability questionnaire
indicate that a waist-mounted vibrotactile display is
acceptable to clinicians. Our aim is to develop this
vibrotactile display further to facilitate information
transfer of respiratory variables and test the device in
a clinical setting. It is hoped that frequent information
transfer of peak airway pressure and minute volume
will aid anesthesiologists in the detection of other
clinical conditions, such as bronchospasm, tube migra-
tion, lightening of anesthesia, pneumothorax, tension
pneumothorax, and malignant hyperthermia.
CONCLUSION
We have shown that a vibrotactile display is ca-
pable of reducing the time needed to diagnose and
treat a simulated critical incident of anaphylaxis. In
our study, clinicians wearing the vibrotactile display
initiated definitive treatment for anaphylaxis earlier
than those in the control group. Whereas the quicker
response time suggests an enhanced SA, our present
data do not support this conclusion. The method used
to measure SA requires further study and validation
in a medical simulation setting. The successful perfor-
mance of the vibrotactile display in our study indicates that
the sense of touch as a medium for communicating
clinical information is worthy of future investigation
in a clinical environment.
ACKNOWLEDGMENTS
We thank the staff, resident, and fellow anesthesiologists
at BC Children’s Hospital, Vancouver General Hospital and
St. Paul’s Hospital who kindly participated in our simulator
study. A special thanks must go to Kathy Ansermino and
Claire Topliss for their assistance in the manufacture of the
vibrotactile display.
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